It started with a hike up to a local mountain top back in 1992. We drove my dad's Audi out the Forrest Service dirt roads, but then we had to walk from quite a ways away from the mountain because the giant ruts were just too much for the little front wheel drive car. It was a fun hike, and the idea came up that a Jeep would really be required to explore these back woods areas.
The Parts Jeep
The Worn Out Hulk
The 2013 Refit
Willies 134 cu in Engines
We started looking around for some sort of a used 4x4 right away, but not having much money to work with the options were very limited. Jeeps were just really expensive.
What we found was an old guy that had two WWII Jeeps advertised for sale. He actually had three of the old WWII surplus Jeeps, two Willies and one Ford. Both of his Willies flat fender Jeeps were fixed up pretty nice, but the 1942 Ford was just a pile of junk. It did start up though and could sort of be driven. He said that he had bought both of the Jeeps that he was selling as parts Jeeps for his original Willies, but he had eventually fixed one of them up as another rather nice complete running vehicle.
The 1942 Ford GPW he had was a mismatch of a bunch of old junk, and he didn't want much for it. I asked him why he wasn't keeping it for a parts vehicle for the one Jeep he was keeping, and he said that he didn't need a parts vehicle anymore himself. He said that he had, over the years, figured out how to do all the maintenance and repairs on those old Jeeps correctly, and he didn't need a parts vehicle anymore.
It really was a pile of junk that he was selling cheap. He said that he had taken good parts off it, and then put the worn out old junk off of his other Jeeps onto this one. He may have done that with a few things, but most of it was actually original. The glaring thing that wasn't original was the motor. Instead of the original flathead it had a later Willies four cylinder.
I didn't like the giant square box on the hood that the tall Carter carburetor and air cleaner stuck up into, and I didn't like that just about everything appeared to be totally worn out. It was however within our meager budget, and it did run and sort of drive. When I told the old guy that I liked the Jeep, but probably wouldn't have the money to fix it up anytime soon he offered to knock another hundred off the price. For $400 we couldn't pass it up, and we towed it home with my dad's 1978 Audi Fox sedan.
The first day we drove our new Jeep around I noticed a severe problem. It ran tolerably well way down low, but it didn't seem to rev up at all. As soon as the engine speed came up to where I thought it should run it just sounded horrible and severely lacked power. I mean it wouldn't rev up at all, it only ran way down extremely low. When I complained about this my dad said I should just run it wherever it seemed to run well. The problem was that the range of engine speeds that it would run over didn't seem wide enough to cover the shifts. Then the brakes went out completely, and we had to drive back with no hydraulic brakes and no emergency brake. There wasn't any mechanical emergency brake at all. First gear in low range was low enough though that it wasn't much of a problem driving the Jeep without brakes. The big engine and a very low gear meant that just letting off the throttle brought the Jeep down to a slow crawling pace, even down substantial hills. Getting down the last big hill to where we had left the Audi was however a bit hair raising without brakes.
We bought a master cylinder rebuild kit, but then we couldn't get the master cylinder off of the frame. The bolts were rusted and severely stuck. Just filling the brake fluid and bleeding the brakes got them working again, but the fluid had to be topped up every few weeks or so as it continued to leak out of the master cylinder.
The more I looked at our new Jeep the more disappointed I was with it's very poor condition. Everything just seemed to be totally worn out. The rear end had a bad hum, the transmission would pop out of second gear sometimes, the steering was loose, the front CV joints clacked horribly when the wheels were turned, the clutch linkage was sloppy and the peddle would stick down sometimes, the motor made horrible noises and on top of it all, the body was rather rusty and falling apart in places. It was drivable though, and it fairly easily traversed most of the rutted up old trails around. At least in dry conditions. The slightest bit of mud or snow stopped it pretty quick as the tires were totally bald. The front tires were totally worn out original type mud tires, but worn all the way down to where there wasn't any center tread left at all. The rear tires were in fairly good condition, but they were highway rib type tires that didn't provide much drive traction in slippery conditions.
The first thing I did was adjust the brakes. This helped some with braking performance, but the brake system was still not very good. My dad filed the points and turned the distributor to adjust the spark timing by ear. We also took the carburetor all apart to make sure everything was clean and working. All we initially found wrong with the carburetor was that the float level was too high. Later we discovered why the float level had been set too high, but at the time we just set it back to stock. This got the motor to run a bit better. The range of low engine speeds that it would run over seemed a bit wider, and it would also rev up and make some power up at the top of the engine speed range. The engine still sounded horrible across a wide range of medium engine speeds, but it sort of worked.
When I hooked an old "engine analyzer" that I got from a friend up I found that my dad had set the dwell on the points pretty close to the factory spec. That was all that the old cheap 1970's "engine analyzer" was; a dwell meter, volt meter and tachometer. With the tachometer I could see that the engine ran smooth up to about 1900RPM, and then it clanked horribly everywhere from 2,000 to 3,000RPM.
I just continued to run the engine bellow the clanking, and it continued to sort of work. It was able to rev out and make some power also, and we did sometimes use the power up at 3,000 to 4,000RPM to get up tough hills. My dad said he thought it ran pretty powerfully for that size and type of engine.
At least it started easily and usually idled fairly well. Sometimes it required the choke to start in cold conditions, but for the most part it always just fired right up with little difficulty. The stock 12V generator didn't work well at all, but it was enough to keep the battery up since the engine usually didn't require much cranking to fire up.
The brass radiator was cracked at the inlet fitting and leaked badly, but with a five gallon jug of water it was possible to drive the Jeep without much difficulty.
We used the old Jeep pretty much like that for a few years. Mostly we just drove it around slowly on small dirt roads, but we did also take it out for a few longer cruises. On one trip on larger dirt roads mostly in high gear high range I noticed that it got 20mpg, which seemed like very poor mileage compared to the 25 to 30mpg that larger and heavier carbureted cars got. I attributed the poor mileage to the low gearing and the motor being an old hunk of junk, although the lack of locking hubs also seemed like it might be a problem.
The shocks didn't seem to work well. The ride was very harsh, and the shocks looked like they didn't fit quite right. The rubber bushings were broken out of most of the ends of the shocks, and it just looked like a bad installation. I took the shocks off one at a time to check their fit. What I found was that they weren't the right size. In the back the shocks didn't extend far enough to allow full articulation of the axle, and in the front the shocks bottomed out just before the suspension bottomed out. Somehow we never got around to getting new shocks though. My dad kept saying that they were good enough like they were.
What I did do was install a set of longer front shackles from a local 4x4 store. The front end had seemed to ride very low compared the rear end, and there wasn't much upward travel before the front shocks bottomed out. The 1.25" longer shackles raised the front end about a half inch, which was just enough to level the Jeep. It looked better when parked, and the ride was somewhat better.
A few years later we bought wheels and tires for the Jeep. We had looked into tires for the old 16" rims, but the options were very limited. I wanted wider tires so that the Jeep wouldn't sink into soft surfaces, and I also wanted some mild tread. What we settled on was a set of 30x9.5-15 tires on 8" steel wheels. The Stockton Wheel brand rims were not all that expensive, and they were available with any offset. I measured the clearance with the front wheels all the way over, and we picked an offset to allow the wider tires to tuck in as close as possible without limiting steering range.
The new Cooper MT tires worked great, providing both a smoother ride and dramatically more traction on all surfaces. The project was however not a success at the time. The clutch began slipping badly. We had known that the clutch was at the end of it's life, but with the bald tires it hadn't seemed like an immediate problem. By avoiding slipping the clutch it hadn't gotten worse. With the new tires though the worn out clutch wasn't good enough. Then the rear ring and pinion locked up also.
That was the end of the Jeep for many years. My dad pulled the rear out and had it rebuilt at a local shop, but he never got around to putting the rear back in. At the same time he pulled the 12V generator off and he hung an internally regulated GM alternator on some funky brackets. He also found a shorter Carter carburetor and stuck that on in place of the tall carburetor. These were all good upgrades, but they never got finalized and the rear end never got put back in.
I was mostly away at school by this time, and I didn't have any interest in the old worn out hunk of junk. It just seemed to need everything, so there it sat for almost two decades.
Finally in the summer of 2013 I dug the old 1942 Ford GPW out and put it back together. I put the rear end back in with new U-joints and new shackles and bushings on the springs. I also replaced both rear brake cylinders, some of the rusted old brake lines and all of the brake shoes. I replaced the GM alternator with a 90A Bosh and built my own funky brackets.
I had long since stolen the 30x9.5-15 tires to use on my Toyota 4x4, but I had some other 31x10.5-15 tires to use instead. On the front I put a pair of partially worn out 31x10.5-15 A/T tires, and for the back I had a nearly new pair of 31x10.50-15 A/T touring tires that I had gotten cheap at a swap meet years earlier. The only thing that was wrong with those nearly new tires was that both beads had gotten kinked, so they wouldn't seal on the rims. To get the bent beads to seal I mixed up some homemade tire goo. I used one part contact cement, one part water and a generous squirt of dish washing detergent as an emulsifier. This worked pretty well. It made for a thick and slippery installation lube that dried hard to fill in the voids around the bent steel bead.
We had a set of cloth covered front seats out of a 1981 Dodge van that seemed like they would be good in the Jeep. The stock seats were pretty abysmal, and we didn't even have the stock passenger side seat. My dad had already taken the under seat gas tank out, so all I had to do was fabricate some custom brackets to bolt the Dodge seats in. I had to tilt the seats back to get enough clearance, and it was a tight fit. There isn't much room for front seats in these old Jeeps. The installation went well though, and the big soft seats turned out to be a dramatic improvement. The built in folding arm rests are a nice touch also. For a gas tank I just threw a 12 gallon Tempo brand boat tank in the back.
My dad's carburetor swap was close to working. He had actually had it fired up and idling a few times, so it did work. It just needed some slight adjustments. I had to file out some of the intake manifold to clear the larger butterfly valve, and there turned out to be some other issues also, but it wasn't all that difficult to get it working.
After sitting outside for over 15 years the points were severely rusted, but everything else worked. I just filed and gapped the points and the engine fired right up. It ran about like it had before, although the rear spark plug was fouled and wouldn't fire at first. After I replaced the spark plug in the #4 cylinder the engine ran pretty much like it had back in the mid 1990's. It still clanked horribly at around 2,000 to 3,000RPM, but it seemed smooth and fairly powerful from 1,300 to about 2,000RPM. Even at 2,000 to 2,500RPM it seemed smooth when first fired up, but then once fully warmed up it was clanking around horribly above 2,000RPM like always.
The first big problem I had with the shorter "Ball and Ball" Carter carburetor was that the engine was starving for gas going up steep hills. The float is hinged at the back of the carburetor, and going up a steep hill the level of gasoline in the bowel dropped dramatically to where the engine wouldn't run at all.
This was similar to a problem we had had with the stock Carter back in the 1990's. The stock Carter had the float hinged at the front, and this had sometimes caused the engine to starve for fuel when going down a hill. This hadn't usually been much of a problem, but we did manage to get the Jeep stuck nose down in a big ditch one time and the motor wouldn't run. The engine had stalled, and wouldn't restart. We had to take the carburetor apart and raise the float level to get the Jeep out of the ditch, and then when we headed up a hill it was flooding and would barely run so we had to then put the float level back to where we had it before. The stock Carter mostly worked fine with that stock float level, it was just with the nose severely down that it would starve for fuel a bit.
With the shorter Carter carburetor with the float hinged at the back it was a much more severe problem. The Jeep just wouldn't go up a hill. I messed around with adjusting the float level, but I couldn't find any acceptable setting. If I raised the float level to where it would go up a little hill then it was flooding really bad on every downhill.
What I finally came up with was to dent in the fronts of the brass floats. This worked perfectly. With some substantial dents knocked into the fronts of the floats I was easily able to find a float adjustment level that worked both for going up steep hills and down steep hills. With the modified floats the Jeep was once again able to go up steep hills with absolutely no trouble with starving for fuel, and the engine was also able to idle well with the nose down on steep descents.
When I took a little test ride cruising along at 1,400 to 1,800RPM in high range and high gear I got 25mpg. That was somewhat better than the 20mpg I had clocked before in more mixed driving with use of second gear around sharp turns and up hills and even a few short detours in low range. Getting the 25mpg I had picked a small paved road specifically for cruising along all in high gear, but without going very fast.
The Jeep was running as well as ever, but I noticed that the mixture was way too rich at the first crack of the throttle. The engine was still running fairly well, but it just felt extremely rich at the small throttle openings required for cruising along at 1,200 to 1,500RPM. It has actually always been like this, but by 2013 I was thinking that I might try to do something about the problem. In looking at the Carter carburetor I noticed that the intermediate circuit traveled past the side of the carburetor body very similarly to adjustable intermediate circuits I have seen on non-automotive carburetors. I got the idea that I might be able to drill and tap the Carter carburetor body for an intermediate circuit adjuster screw.
I decided to give this a try, and I was blown away by the results. Not only did the engine run a lot better at small throttle openings with the intermediate circuit leaned out, but the response of my new intermediate circuit adjuster screw was spot on. The Carter "Ball and Ball" carburetor appears to have been designed to work with an intermediate circuit adjuster screw, that screw just wasn't included on the stock automotive carburetor. I was amazed and delighted that the engine ran so much better at small throttle openings, but I was also somewhat alarmed that this automotive carburetor had come stock setup so poorly.
The difference was quite dramatic. Not only did the overly rich sound and black exhaust at small throttle openings go away, but the throttle response was much crisper at small throttle openings also. The engine made more power with smaller throttle openings, and there was simply more torque available everywhere down at 1,200 to about 1,700RPM. Beyond about 1,700RPM or so the wider throttle openings were no longer on the intermediate circuit, so there was no noticeable difference up at those higher engine speeds.
The Jeep was working so well that I made some other upgrades. I finally got around to buying those new shock absorbers also. I jacked the Jeep up at one corner to measure for the shocks. To allow full articulation would have required somewhat longer shocks than were available, but I found that I could get pretty close. It turned out that the back needed much longer shocks than the front. The shocks that had been on there were the same front and back, and that hadn't worked out. Those shocks didn't have as much range of travel either. Looking in a Monroe catalog I found some shocks that were the right length, and also were listed for rather light weight vehicles. The rear shocks go on both Chevy LUV pickups and old Toyota pickups. The slightly shorter front shocks were listed only for 1970's two wheel drive Toyota pickups.
The new Monro-matic shocks worked great. They were a bit stiff for the Jeep since they are for somewhat heavier vehicles, but they were close enough to work darn well. Compared to the old shocks that had been on the Jeep these new shocks provided a dramatically smoother ride at all speeds over all types of bumps, and the damping felt very substantial even at higher speeds. Along with the squishy Dodge seats the new shocks provided a dramatically more comfortable ride. A vast improvement.
I finally installed locking hubs, which turned out to be an easy upgrade. In the past I had never seen locking hubs listed for the WWII flat fender Jeeps, but then in 2013 I dug deeper and compared the bolt patterns and spline counts on the various Jeep models. What I found was that pretty much all of the Jeeps from the 1940's and into the 1960's used the same spline count and the same bolt pattern. When I ordered a set of locking hubs for a later 1950's Jeep I found that they bolted right onto the 1942 GPW without any modification required.
The locking hubs would be good for saving some gas in high speed highway cruising, but what I find them most useful for is providing two wheel drive low range. With the rather close ratio three speed transmission first gear tends to feel pretty high in high range, even with the stock 4.88:1 ring and pinions. For most maneuvering and slow driving low range is much better. The problem was that the CV joints clanked and clacked horrendously. They kept on working and never gave any sign of trouble under a load, they just clacked horrendously with the wheels turned in four wheel drive. The locking front hubs allows use of the low first gear in low range to easily and casually drive around slowly without the horrendous clanking. Steering effort is also lighter in two wheel drive than in four wheel drive, especially with the wheels turned all the way on one side or the other. Being able to use low range also takes a lot of load off of the clutch. Pulling out in high range, especially up a bit of a hill, tends to require some substantial clutch slipping, so no doubt that is why the clutch disk was worn out. It still needs a new clutch disk of course, but it hasn't actually seemed to get worse with me driving it gently in low range most of the time.
It's nice to have low range since first gear is so tall, but the difference between low range and high range is actually excessive. Third gear in low range is noticeably quite a bit lower than second gear in high range. In low range it always feels like it needs another gear, even going pretty slow on small dirt roads.
Another upgrade was a winch. There was already a big custom front bumper installed, and it looked like there had been a winch on there sometime in the past. Having played around some with trying to winch heavy things around I had come to a clear understanding of the limitations of wrapping cable around a long drum. The cable has to go on perfectly coiled, otherwise it just gets shredded in short order with any sort of a substantial load on it. I decided that a swiveling mount for the winch would be a good idea. I used the turn table on the milling machine to cut radius slots in a piece of 1/4" steel plate. The winch mounts to the plate using counter sunk bolts, and then the plate swivels on a central counter sunk bolt. The plate is then secured by a bolt and washer in each of the radius slots.
This setup works amazingly well. Instead of having to align the cable exactly to the winch, the winch can just be turned to line up with wherever the cable happens to be. As the jeep is winched forward the angle changes and it is necessary to stop, take the load off the cable, and then readjust the winch. This is however pretty simple and easy. When using the winch to pull something else other than the Jeep the swivel mount is even more useful. Instead of having to line the Jeep up to pull straight, the swivel mount can just be turned to get perfect alignment of the winch to the cable. Just a small 5,000 pound UTV winch with 1/4" steel cable has seemed perfectly adequate for all purposes. The next upgrade is going to be dynema line instead of the cable, but so far the cable has been holding up. Using dynema line instead of cable has become very popular on Jeeps over the past few years.
The leaking radiator was finally seeming to be a huge problem, so I replaced it with a radiator for a Chevelle that went in with only some minor bending of tabs and a few custom spacers. Not having to fill the water all the time seemed like a substantial upgrade.
For a while I had also been driving around with the same leaky master cylinder, pouring brake fluid in every month or so. The leak didn't seem to be very fast, but then when it would sit for a while all the brake fluid would leak out and I would have to bleed the brakes to get them working again. Finally I figured out how to get a better cheater bar on the wrench, and I was able to break the stubbornly rusted old nuts and bolts out. The master cylinder didn't look like it was in very good condition, but the new seal fit nicely and I decided to give it a try anyway. I just cleaned the inside of the cylinder up lightly with 600 grit silicon carbide paper and suck the new parts in. Amazingly the rebuilt master cylinder worked perfectly, and hasn't leaked a drop of fluid. Not only does the fluid now stay in the brake system, but the feel at the peddle is firmer and much more consistent and the brakes work better than they ever have before.
The little 9" drum brakes are of the fixed pivot type, so they aren't exactly powerful. They are however exactly the same going forwards and backwards, which is a nice feature on a Jeep. They are also exactly the same front and rear which means that the rear brakes lock up first under heavy braking, unless of course it's in four wheel drive which removes all brake bias problems. Being fixed pivot brakes the main thing is that they just aren't very powerful. Amazingly though with a good master cylinder, four good wheel cylinders, good shoes and adjusted evenly they do work tolerably well for the small 4x4.
In the summer of 2013 I also overhauled the electrical system, installing a new headlight switch, a new horn on the same old horn button and horn relay and I got all the lights working. I also installed a permanently mounted tach on the dash board in place of the missing original speedometer. The original oil pressure gauge and temperature gauge still worked, so adding the tachometer and a volt meter in place of the old amp meter filled all the holes to make the interior look complete.
I had known that the later Willies inline four was very similar to the four cylinder flatheads that were stock in all the 1940's Jeeps, but only in 2013 did I figure out the extent of the similarities. Not only is it the same 134 cubic inch displacement with the same 3.125" bore and 4.375" stroke dimensions, but the crankshafts, rods and pistons are actually interchangeable. It is in fact the exact same bottom end.
The story of the development of the Jeep is actually very interesting. It was back in the late 1930's that the U.S. Army began developing what they called a "field car". The Germans got a field car into service first with the Volkswagen based rear wheel drive Kuebelwagen in the 1930's, where the American field car didn't see light until the early 1940's.
The basic gist of the story of the Jeep is that Bantam won the U.S. Army design competition with their prototype, but then Willies was awarded the production contract because Bantam was too small to fill the orders. The production Willies was a modification of the original Bantam, and it got a lot heavier. Then when Willies was too small to fill the orders Ford was contracted for mass production. Just as Willies had modified the original Bantam, Ford insisted on making a few changes of their own. The contract specified that Ford was supposed to build parts that were fully interchangeable with the existing Willies models, but this wasn't fully honored. The most obvious change was from the fabricated grill to the stamped steel Ford grill, but there were other changes also. When it came to transmission and drive shaft installation details Ford just did it the way they wanted to, and then Willies production was shifted to maintain full interchangeability of parts. So the little known reality is that all of the later Willies Jeeps from after 1942 are actually Ford vehicles produced by Willies. The rare and unusual WWII Jeeps are the early Willies produced before the mass production contract was awarded to Ford in early 1942.
The three companies that entered the U.S. Army design competition were Bantam, Willies and Ford. Bantam won that original design competition, but their design was mostly scrapped when Willies won the production contract. The funny thing is that the production Willies looks a lot more like the Ford prototype than the Bantam prototype, and then in the end it was Ford that produced the vast majority of all WWII Jeeps.
The original design requirement specified by the U.S. Army was a maximum unladen weight of 1500 pounds, and that was never officially rescinded. The brass plaque on all of the production Ford Jeeps specifies the unladen weight as 1488 pounds. The reality though is that they weigh more than 2000 pounds empty, and this is reflected in the official net shipping weight. They were supposed to weigh less than 1500 pounds empty, and even though they came out vastly overweight nobody admitted to this until they actually had to be loaded onto a ship.
The original 134 cubic inch flathead was a turd. It was rated at only 50hp output. It's a lot of displacement, but as a 6:1 flathead it wasn't much of a performer. Even with the lackluster flathead performance top speed was said to be 65mph at 3,600RPM.
The 1953 through 1971 Willies is more of a screamer. It has the same long 4-3/8" stroke length of the 1930's flatheads, but the intake valves are in the cylinder head. These 1953 through 1971 Willies engines were originally known as "F-head" engines, and the earlier flatheads were known as "L-head" engines. That was too confusing though, because F-head sounds too much like flathead. I have heard them called "S-head" engines.
In any case they have the intake valves in the cylinder heads, but the exhaust valves are still in the block. This results in an elongated combustion chamber somewhat like a flathead, but the overhead intake valves do flow a lot better. The 1953 Willies was rated at a whopping 72hp at 4,000RPM, a big step up from just 50hp from the 134 cubic inch flathead it replaced. And even that 72hp at 4,000RPM rating is rather conservative. A 4-3/8" stroke length 134 cubic inch engine tends to be able to make that 72hp output already by about 3,200RPM. The reality is that the 134 cubic inch Willies F-head pulls harder and harder as the engine speed is increased from 3,100RPM up to at least 3,500RPM, even on spectacularly weak gasoline. That 3,500RPM engine speed would tend to be at least 78hp from the 4-3/8" stroke length 134 cubic inch engine. Beyond 3,500RPM the stock Willies engine is a too choked off to flow well, and cylinder filling drops off. On powerful gasoline it will very easily continue to make power to 4,000RPM and beyond, but it is going extremely flat up there. The stock camshaft is very small, more for 1,500 to 3,500RPM engine speeds than 3,500 to 5,000RPM engine speeds.
In 2014 I replaced the rod bearing inserts in my Jeep. The crankshaft was pretty much garbage, but I decided to give another new set of inserts a try anyway. The rod journals were fairly smooth and mostly uniform, but they were 0.007" out of round. Yes seven thousandths of out or round, not seven ten-thousandths out of round. The old inserts were worn down quite severly, but not commensurate with the completely toasted rod journals. Obviously the inserts had already been replaced quite a few times on these same rod journals. The old inserts were however worn so far down that new inserts reduced the oil clearance substantially.
The new inserts didn't totally eliminate the horrible sounds, but there were some changes. The huge clanking around at 2,200RPM did diminish considerably, and the oil pressure has been staying up a bit better. For a while the engine seemed to be actually working tolerably well with good smooth operation all the way up to about 2,300RPM. To break in the new inserts I kept the engine speed down below 2,000 or 2,300RPM all the time. After having driven the jeep around like this for a while I gingerly revved it up more again. What I noticed was that when the oil was cold there was no clanking around at any engine speed, but once the oil warmed all the way up and the oil pressure dropped then the clunking and clanking around above 2,000RPM would come back pretty bad. When the oil was still cold and thick the engine was smooth and fairly powerfull at all engine speeds from 1,500 to 3,000RPM.
Then one day in the spring of 2016 I noticed that the long stroke length engine was entering late compression ignition mode at 2,500RPM. It was getting somewhat harsh with wide throttle openings at 2,500RPM, but the power didn't increase at that 2,500RPM engine speed. Obviously this was some rather fast flame front travel speed gasoline that made just as much power at 2,500RPM in full flame front travel mode as in late compression ignition mode in the long 4-3/8" stroke length engine. The engine was still able to rev up smoothly from 2,500RPM to 3,000RPM at smaller throttle opengins, only at wide throttle openings did it get harsh at 2,500RPM.
Then all of a sudden in the summer of 2016 the long stroke length Willies engine started detonating at 1,600 to 2,000RPM. Just horrible detonation as soon as the engine speed hit 1,600RPM. Instead of smooth and fairly strong torque at 1,600 to 2,000RPM all of a sudden it wouldn't make torque at all at those engine speeds. At the same time I noticed that the minimum engine speed had dropped from around 1,200 or 1,300RPM down to about 1,000RPM.
Back in the 1990's and in 2013, 2014 and 2015 the long 4-3/8" stroke length Willies engine ran along smooth and fairly strong from 1,300 to about 2,000RPM, but it didn't like to go down much bellow 1,300RPM under a load. Then all of a sudden in 2016 it wouldn't work at all from 1,600 to 2,000RPM, but the minimum speed limit of 1,300RPM also disappeared. It used to be a 1,300 to 2,000RPM range of engine speeds, but then all of a sudden the range of engine speeds dropped down to 1,000 to 1,600RPM. That didn't work well. Not only is there dramatically less power at 1,000RPM than at 1,300RPM, but it actually seems like a narrower range of operable engine speeds.
At the same time another problem showed up; cutting out at 3,000 to 3,500RPM. Sometimes cutting out in the form of the power just quitting all of a sudden, but mostly it was a lean stumble where the engine would start missing severely with hard cutting in and cutting out. The long stroke length 134 cubic inch engine used to always sound very bad from 2,000RPM up to about 2,800RPM, but it also was able to rev out and make some power at 3,000 to 4,000RPM. Then all of a sudden it was often horrible lean feeling and cutting out like crazy at wider throttle openings up above about 2,800 or 3,100RPM.
There are some other differences also. The long stroke length engine is actually smoother from 2,200 to 2,700RPM than it was back in the 1990's, but it still won't make much torque at those engine speeds. The big torque always comes up above about 3,000RPM, that has always been true and will always continue to be true. Sometimes the torque comes on pretty good way down around 2,700 or even 2,500RPM, and other times it is only above 3,100RPM that big torque is available. What is always true though is that the torque increases dramatically as the engine speed is increased above 2,300RPM. Sometimes when the engine is detonating badly at 1,600 to 2,000RPM the torque increases quite rapidly from 2,300 to 2,600RPM, where at other times when the engine is detonating badly at 1,600 to 2,000RPM the torque seems pretty flat all the way from 2,200 to 2,800RPM with a dramatic increase somewhere right around 3,000RPM. It hasn't always been the same, but the 4-3/8" stroke length engine always seems to run very poorly over some range of engine speeds around 2,200 to 2,900RPM.
So I used to have a crappy old Jeep that only liked to run way down at 1,300 to 2,000RPM or up above about 2,800RPM. Now the same engine will pretty much only run down bellow 1,600RPM, although it does lug down to 1,000RPM and sometimes even 900RPM without much protest. And it is very inconsistent now also.
Sometimes the detonation isn't as bad. That is, sometimes I can crack the throttle open a bit and get a small amount of smooth power all the way up to 1,900 or 2,000RPM without detonation. It still often makes power above 3,000RPM also. Power usually seems weaker than it was at 3,700 to 4,000RPM, but it will often still pull reasonably well from about 2,600 to 3,500RPM. The other thing I notice is that there is a strong correlation between bad detonation at 1,600 to 2,000RPM and cutting out above 3,000RPM. When it is able to take a bit more of a throttle opening and deliver a bit more smooth torque around 1,600 to 1,900RPM it also pulls much harder up above 3,000RPM without cutting out.
So that's what a long stroke length engine is like. It runs much better and makes a lot more power on more powerful higher temperature of combustion potential gasoline, but the 4-3/8" stroke length is still way too long to do well at anything other than idling bellow 2,000RPM with a firmly closed throttle. On weaker gasoline the performance just falls apart completely. As long as the gasoline isn't severely watered down with ethanol or other specialty low energy density additives the 4-3/8" stroke length engine is always able to make some fairly respectable torque over some narrow range of engine speeds around 2,600 to 3,700RPM. That torque is weaker and tends to come over a narrower range of engine speeds on lower temperature of combustion potential gasoline, but as long as the energy density is not too low for the main jet size then there is some torque available somewhere between 2,600 and 3,500RPM. What disappears on the lower temperature of combustion potential gasoline is the torque at 1,600 to 2,000RPM.
Sometimes turning the distributor one way or the other helps a bit, but it is usually the stock spark timing or something very close to it that works best. Advancing the spark timing can help with delivering power up at 3,000 to 4,000RPM, but usually isn't necessary.
The spec for the 1953 and later 134 cubic inch "F-head" is 5 degrees BTDC at low idle, and that is where I usually run it. The advance actually starts to pull in a bit as low as about 500RPM, so checking the spark timing requires backing off on the idle stop screw to get it low idling way down very low to get an accurate reading. Normal low idle of 700 or 800RPM usually gives about a degree or two of advance so that the low idling spark timing looks like it is up at 6 or 7 degrees BTDC. The stock recommended low idle speed is 550RPM, and it can often be made to low idle down that low. What I find though is that with the idle mixture and idle stop adjusted just right the low idle might be way down around 500 to 600RPM in the first minutes of operation, but it usually comes up some once the engine has fully warmed up.
The spark advance comes on quickly as the engine speed is increased above low idle, and it is already up to 15 degrees BTDC at 1,900RPM. Maximum advance is 24 degrees BTDC at about 2,800RPM, but most of that advance comes by 2,500RPM. The advance comes on rapidly up to about 22 degrees BTDC at 2,500RPM, and then the last two degrees comes much more gradually as the engine speed is increased further. By 1950's through 1990's standards it's not much spark advance, but then the bore diameter is only three and an eighth inches.
In late 2016 and early 2017 I have tried backing off on the spark timing to get rid of the detonation at 1,600 to 2,000RPM, and this only sort of works. Backing off on the spark timing does indeed allow wider throttle openings at 1,600 to 2,000RPM, but it doesn't necessarily deliver significant increases in torque on very weak gasoline.
With the engine warmed up I have backed off as far as 10 degrees of crankshaft rotation for 5 degree ATDC cranking and idling spark timing, and the engine did continue to run with that ridiculously late spark timing. Not well, but it did run. With that dramatically later spark timing the engine was able to take a much wider throttle opening at 1,600 to 2,000RPM, but torque only increased very slightly. Backed off that far it wouldn't rev up though, and there was essentially no power and tons of cutting out. When the gasoline is very weak the big 4-3/8" stroke length engine just won't run at 1,600RPM to 2,400RPM.
Backing off half as far for TDC starting and idling spark timing doesn't seem to make much difference on the three inch bore engine. It still seems to run very much the same as with stock spark timing on the weak watered down and low temperature of combustion potential gasoline. Backing off on the spark timing did allow slightly larger throttle openings and there was a bit more torque up to slightly higher 1,800RPM engine speeds, but the difference just wasn't all that dramatic. It's not so much that there isn't enough spark advance, it's more like the weak gasoline just won't make torque above about 1,800RPM in the long 4-3/8" stroke length engine. It's like the mean piston speed at 1,800RPM in the 4-3/8" stroke length engine is actually too high for full flame front travel mode operation on that extremely dramatically weaker gasoline.
Back in the 1990's and in 2013, 2014 and 2015 there was sometimes some benefit to turning the distributor 1/32" or so in one direction or the other for about two degrees of crankshaft rotation change in the spark timing. Sometimes backing off that little bit made all the difference in smoothing out the engine operation everywhere from 1,900 to 3,000RPM.
The vacuum advance was disconnected when we got the Jeep back in the early 1990's, and I have always run it with the vacuum advance disconnected. Several times I have tried hooking the vacuum advance back up, and all it does is cause horrendous loud and harsh clanking at all engine speeds.
If this mostly dramatically lower temperature of combustion potential gasoline is really what gasoline is supposed to be then the 4-3/8" stroke length is so long that it essentially can't be made to work at all. On this dramatically lower temperature of combustion potential gasoline the 4-3/8" stroke length Willies engine is running about like a 5.5" stroke length gasoline engine runs on the hotter burning gasoline that has been considered normal. That means crappy. Hardly running at all. Burning loads of gasoline, but not producing usable power output. Of course some big power is still always available over a narrow range of engine speeds around 3,000 to 3,500RPM, but above and bellow is very spotty.
There are a couple of different ways to describe the change in performance of the 4-3/8" stroke length Willies engine when switching to weaker, lower temperature of combustion potential gasoline. Perhaps the most easily articulated description would be that the 4-3/8" stroke length Willies engine used to reliably make power between 2,600 and 4,000RPM, and now after the summer of 2016 that range of upper engine speeds has shrunk to as little as just 3,100 to 3,500RPM. Back in the 1990's there was always some harsh clanking torque starting as low as somewhere around 2,500 or 2,700RPM but the torque built steadily up past 3,000RPM. That was on rather high temperature of combustion potential gasoline back in the 1990's. Then in 2013, 2014 and 2015 same engine ran similarly but perhaps a bit more smoothly at all engine speeds and also perhaps somewhat more powerfully at 1,300 to 2,000RPM. Then after the summer of 2016 the torque bellow 2,000RPM simply disappeared and horrible detonation showed up at 1,600 to 2,000RPM. At the same time the power above 2,500RPM became spotty, with cutting out and stumbling at large throttle openings above 3,000RPM sometimes being very severe.
Perhaps the best way to describe this change is in terms of the range of operable engine speeds shrinking from 2,600RPM to 4,000RPM back in the 1990's down to just 3,000 to 3,500RPM since the summer of 2016. This loss of top end power and a narrower range of engine speeds clearly points to weaker gasoline. There are however other ways to describe the change. Somewhat confusingly the engine now often appears to have to rev higher to around 3,000 or 3,100RPM before the torque comes on at all, where back in the 1990's and in 2013, 2014 and 2015 the torque started to build a bit below 3,000RPM. This is confusing because it is weaker and lower temperature of combustion potential gasoline that is causing the engine speed to need to be higher to make torque in the same 4-3/8" stroke length engine. This seems entirely backwards.
Another way to describe the difference is in terms of performance bellow 2,000RPM. Back in the 1990's and in 2013, 2014 and 2015 pretty good smooth torque always seemed to be available bellow 2,000RPM, where now after the summer of 2016 the torque at 1,600 to 2,000RPM has entirely disappeared and even down at 1,300 to 1,600RPM the torque sometimes feels weaker than it was before. The last bit of information is that back in the 1990's and in 2013, 2014 and 2015 the minimum engine speed for the 4-3/8" stroke length seemed to be about 1,200 or 1,300RPM, where now after the summer of 2016 the same 4-3/8" stroke length engine is able to pull down to 1,000RPM and sometimes even 900RPM.
In the 4-3/8" stroke length engine higher temperature of combustion potential gasoline results in more torque, more power, wider ranges of operable engine speeds and a higher engine speed for peak output, where lower temperature of combustion potential gasoline in the same engine results in lower torque production, less power, narrower ranges of operable engine speeds and a lower minimum engine speed. The engine speed where the difference is most dramatic is down low at 1,600 to 2,000RPM where good strong smooth torque is available on the higher temperature of combustion potential gasoline and the lower temperature of combustion potential gasoline causes very harsh detonation and a severe loss of torque over the same range of lower engine speeds. Up at 2,600 to 3,100RPM there is also often a rather dramatic difference, with the higher temperature of combustion potential gasoline delivering considerably more torque at those engine speeds.
In the end though it is all about ranges of engine speeds. On more powerful higher temperature of combustion potential gasoline the 4-3/8" stroke length Willies engine runs fairly well everywhere from 1,300 to 4,000RPM with only a small gap in the middle at around 2,000 to 2,500RPM. On weaker lower temperature of combustion potential gasoline the gap in the middle expands to as much as 1,600 to 3,100RPM and the ranges of operable engine speeds shrink to 3,100 to 3,500RPM up top and 1,000 to 1,600RPM down low. Clearly the 4-3/8" stroke length is dramatically too long.
I did check the gas mileage once after the horrible detonation at 1,600 to 2,000RPM showed up, and it was very poor. I headed out with what I thought was four gallons in the tank, but I had another gallon and a half in another container. Climbing up to 4,000 and 6,000 feet of elevation the engine was still suffering from horrible detonation at 1,600 to 2,000RPM, and power at 1,200 to 1,600RPM was seeming weak but smooth and usable. At the higher elevations the engine was able to take wider throttle openings at 1,600 to 2,000RPM before detonating, but torque was still extremely low. It took a long time to get up into the mountains, even though it was a fairly large dirt road. Then the tank ran dry after just 34 miles. It seemed that most of the four gallons of gasoline had disappeared overnight, because it probably couldn't have gotten just 8mpg even running that poorly. I added the additional gallon and a half of gasoline I had and only made it 27 miles further traveling in high range high gear and going mostly downhill. That's just 18mpg while dropping from 6,000 feet to 1,000 feet over 27 miles on a mostly fairly even gentle downgrade.
Obviously the worst detonation at 1,600 to 2,000RPM is caused by very weak gasoline that also causes extremely low gas mileage. On more powerful gasoline the 4-3/8" stroke length Willies engine makes pretty respectable torque everywhere from 1,300 to 2,000RPM, and on that more powerful gasoline it is also able to quite easily turn in 20 to 25mpg runs in high range high gear despite the very low 4.88 gears.
About the only thing that eliminates the 1,600 to 2,000RPM detonation on the weaker gasoline is a shorter stroke length, and that is no doubt why Ford, Chevy and Chrysler all switched to shorter 3.0 to 3.75 inch stroke length engines in the 1950's and mostly discontinued the old 4.0 and 4.375 inch stroke length engines. The modern 1950's through 1980's carbureted 3.25 and 3.5" stroke length automotive engines only sometimes suffer from detonation at 1,000 to 2,500RPM, and when they do detonate at those engine speeds it is usually just a tuning problem.
There are things that case worse low engine speed detonation. Obviously a high compression ratio tends to be difficult to get to work with very low pressure gasoline, but interestingly it is mostly long stroke lengths that causes the difficult to tune out detonation at 1,500 to 2,500RPM. Higher compression ratio engines lack torque in the 1,000 to 2,500RPM engine speed range, but as long as the stroke length is sufficiently short and the camshaft is appropriate for the application they are still able to idle along smoothly making some small amounts of power at small throttle openings. The main reason that the stroke length is so important is that there is too much of a gap between the engine speeds that work well in full flame front travel mode and the engine speeds that work well in late compression ignition mode in longer stroke length engines. For late compression ignition mode to work well the engine speed has to be up above about 3,000RPM even with a long stroke length, but then a long stroke length engine has a hard time making power at 2,000 to 3,000RPM in full flame front travel mode. The longer the stroke length the worse this problem becomes. Shorter stroke length engines can rev higher in full flame front travel mode, and this substantially covers the gap to provide seamless smooth torque generation. As far as eliminating the bad detonation at 1,300 to 2,500RPM the ideal stroke length appears to be about 3.0 to 3.25 inches. Shorter 2.0 to 2.25 inch stroke length engines attain higher overall operational efficiency and can be made to run better over wider ranges of engine speeds, but then they don't tend to idle down as well in full flame front travel mode either so the 1,300 to 2,000RPM range of engine speeds actually becomes mostly irrelevant.
There are also a lot of tuning problems that can cause bad detonation at 1,000 to 2,500RPM in three to four inch stroke length engines. The main culprit is just too much spark advance. Usually just about any engine will suffer from bad detonation down low if the spark timing is advanced. The only thing that eliminates detonation with large amounts of spark advance is extremely low compression ratios, but then that eliminates all late compression ignition at all engine speeds and there is just absolutely no torque and no power anywhere above about 2,500 or 3,500RPM depending on the size of the engine and how spectacularly powerful the gasoline happens to be. On very high pressure race gas this can happen up at as high as about 10:1 compression ratios, on most types of normal gasoline though too much spark advance will cause bad 1,000 to 2,500RPM detonation at much lower compression ratios.
Obviously the camshaft has a lot to do with it also. A big high performance camshaft slightly reduces cylinder filling bellow 2,500 or 3,500RPM, and that tends to reduce detonation down low. The reduced cylinder filling from a big camshaft doesn't increase pumping losses the way that a closed throttle does, so the gains in reduced detonation at 1,000 to 2,500RPM from a big camshaft tend to be somewhat more significant than might be expected. The simple fact that the engine then also makes more power up to higher engine speeds also tends to reduce the problems associated with 1,000 to 2,500RPM detonation. If the engine will pull well over a wide range of engine speeds up above 3,000RPM then operation way down low in full flame front travel mode doesn't have to be so all important.
Clearly a lower compression ratio would tend to reduce detonation, but torque production at 1,000 to 2,000RPM doesn't necessarily increase much with a lower compression ratio. Obviously if the compression ratio is so high that the engine can't take any throttle opening even with the spark timing backed off as far as possible for that bore diameter and engine speed combination then it's not going to work at all in full flame front travel mode. That's an extreme case though. With that high of a compression ratio and a small camshaft an engine just won't work at all in full flame front travel mode at any engine speed.
Lower compression ratios do allow more spark advance, but increasing the spark advance beyond where the engine already is able to run and make torque is going to yield only very slight increases in torque. Since lowering the compression ratio also tends to reduce the thermodynamic efficiency of any engine there just isn't much opportunity for increasing torque generation with reduced compression ratios. There tends to be a critical minimum spark timing for a certain bore diameter/engine speed combination on any particular type of gasoline. Less spark advance than this critical value and the engine essentially won't run at all. Near that critical spark advance value slight changes in spark timing have a rather large effect. A bit latter spark timing results in dramatic reductions in torque and the engine gets very dirty, and just another degree or two less spark advance and the engine becomes so prone to stalling that it essentially won't run at all.
Just what happens as the spark timing is advanced beyond that critical minimum value for full flame front travel mode operation depends a lot on the engine speed. At very low 1,000 to 1,800RPM engine speeds a small amount of additional spark advance results in some significant gains in torque production, but additional amounts of spark advance don't make much difference at all. At higher engine speeds torque generation in full flame front travel mode does continue to increase with increased spark advance, but the gains are modest. Lots of spark advance in full flame front travel mode is good for reducing unburned hydrocarbon emissions and preventing spark plug fouling, but torque generation tends to remain about the same all the way down pretty close to the critical minimum spark advance value for that bore diameter and engine speed combination on the gasoline being used.
Absolute maximum torque generation in full flame front travel mode would be found with a low enough compression ratio that a wide throttle opening can deliver maximum cylinder filling with plenty of spark advance. Interestingly though a rather large portion of this amount of torque can be generated in full flame front travel mode with a higher compression ratio and a partially closed throttle. The stickler is just that the throttle can't be fully opened until the engine speed comes up to where late compression ignition mode can work. A big camshaft can help out a lot in this regard. The reduction in cylinder filling afforded by a later intake valve closing time is more efficient because it doesn't increase pumping losses the way that a closed throttle does, and perhaps even more importantly the throttle can be opened farther without detonation occurring.
If the goal is to prevent all detonation below 2,500RPM, even with a wide open throttle, then clearly either a big camshaft or sophisticated electronic controls of some type would be required. An advance curve is also important if all detonation below 2,500RPM is to be prevented. Fixed spark timing pretty much only works down to slightly below the minimum engine speed for late compression ignition, which is somewhere around 2,500 to 3,500RPM depending on the stroke length and what type of gasoline is used. For a long 4-3/8" stroke length clearly the advance curve shoulder needs to be way down at around 2,500RPM or perhaps even 2,300RPM for very weak low temperature of combustion potential gasoline. Short two inch stroke length engines on the other hand work well with the advance curve shoulder all the way up around 3,200 or 3,500RPM, but the exact ideal advance curve shoulder location does depend on the temperature of combustion potential of the gasoline that is actually used.
For operation in late compression ignition mode it is the location of the advance curve shoulder that is most critical. For operation down lower in full flame front travel mode it is the shape of the advance curve that is of critical importance. It tends to be something pretty close to just a straight line that is the best shape for the advance curve, but the slope of that line and the lower intercept at low idle depend on the bore diameter and the flame front travel speed of the gasoline that is actually used. There are however some tricky things about what advance curve actually works best. Bigger bore engines tend to need more spark advance, but exceeding about 25 degree BTDC spark timing does tend to preclude attaining the latest possible time of late compression ignition. This means that big bore engines don't necessarily actually benefit from a more steeply sloping advance curve. It would be expected that a big bore engine would need more steeply increasing additional advance as engine speeds are increased from 1,500 to 2,500RPM, but when the earliest possible spark timing for 3,000 to 4,000RPM operation is 26 degrees BTDC there just isn't room for a steep advance curve. Instead a big bore engine has to rely on a sort of ridiculously low advance curve shoulder and a more gradually sloping advance curve down to low idle. Big bore engines do benefit from an additional advance curve up to maximum engine speed, but from 3,000 to 8,000RPM the slope of the line has to be very gradual.
Small bore engines would be expected to work well in full flame front travel mode with more gradually sloping advance curves up to 3,500RPM, but the reality is that the ideal shape ends up being remarkably similar over a wide range of bore diameters. The reason for this is that getting small bore engines to run well way down low in full flame front travel mode does actually tend to require rather late spark timing. What actually is dramatically different with small bore engines is that beyond 3,500RPM the spark advance has to be saying flat or even getting later. With two to three inch bore engines just flat spark timing from 3,500RPM on up to maximum engine speed seems to be best, where smaller bore engines can benefit from the spark timing actually backing off gradually from about 5,000RPM out to maximum engine speed.
What it really comes down to is that the exact ideal shape of the advance curve down bellow 3,000RPM depends a lot on the stroke length also. For stroke lengths less than about 3.25 inches the shape of the advance curve is mostly about delivering best possible light load performance since bad detonation bellow 2,500RPM doesn't tend to be much of a problem. For longer four inch stroke length engines though the shape of the advance curve from 1,000 to 2,300RPM is critical for delivering usable torque without detonation. And the longer the stroke length the more important it is to get some substantial torque delivery way down at less than 2,000RPM because those longer stroke length engines can't efficiently support light to medium loads up at higher engine speeds. A four inch stroke length engine might be able to belt out some big torque at around 2,700 to 4,700RPM, but it is only going to be able to do it reasonably efficiently under heavy loads.
And there are a few little tricky things about mixture ratios that have some effect on detonation problems. Ironically, and counter intuitively for many people, overly rich mixtures actually cause worse detonation problems in long stroke length engines. The overly rich mixture reduces the actual flame front travel speed, so the engine can't make as much power in full flame front travel mode at elevated engine speeds. Wider throttle openings are then selected trying to get the expected torque generation and detonation occurs. Once detonation occurs with the overly rich mixture it is harsher and more damaging because of the larger amount of combustion taking place. Plain and simple, more fuel can be burned in late compression ignition mode than in full flame front travel mode. Overly rich mixtures always cause a more abrupt transition from full flame front travel mode to late compression ignition mode, and that means worse detonation at 1,500 to 2,500RPM in long stroke length engines.
There is a flip side to the mixture ratio issue though. At lower mean piston speeds dumping tons of extra fuel in can eliminate detonation. Huge amounts of gasoline dumped in displaces intake air, and that certainly can prevent late compression ignition. Dumping huge excess amounts of gasoline in only works to eliminate low mean piston speed detonation, way down low where the slower effective flame front travel speed can still produce torque in full flame front travel mode. That is the 1,000 to 1,800RPM detonation in 3.0 and 3.25 inch stroke length automotive engines. Way down at those much lower mean piston speeds an extremely overly rich mixture certainly can reduce detonation, but dumping all that extra gasoline in obviously isn't a good idea. Light load efficiency plummets, the engine oil gets dirty faster, emissions skyrocket and throttle response feels sluggish and heavy.
An extremely overly lean mixture, such as running 30% ethanol in a carburetor jetted for gasoline, can also cause detonation problems. If the mixture is so lean that torque generation in full flame front travel mode severely drops off then all sorts of problems tend to crop up; especially in longer stroke length engines. Taken to an extreme a very lean mixture might cause stumbling and missing in full flame front travel mode, but late compression ignition mode operation still sort of works. At that extremely overly lean mixture ratio detonation may actually be required to get an engine to rev past 1,500 or 2,000RPM at all. In that case clearly the mixture is too lean. The most likely culprit is large quantities of ethanol or other specialty low energy density additives in the gasoline. If it is not possible to switch to gasoline, then increasing the fuel flow rate certainly will deliver much better operation at all engine speeds. The problem of course is that a half and half mixture of gasoline and ethanol probably won't be available for long because it is much more expensive and severely hurts performance and efficiency. When the gasoline supply switches back to gasoline then the fuel flow rate also needs to be switched back to the previous values. With a carburetor this is difficult to impossible, especially if it is a butterfly valve type carburetor. There just isn't much adjustment available, and drastic modifications to run alcohol tend to be mostly a one way deal. It is much easier to drill out passages and orifices than to tighten them back up. The point is that large quantities of alcohol or other specialty low energy density additives in the gasoline wreak havoc on carbureted engines.
Something I have always noticed about the 1942 GPW is that it goes better over uneven terrain than any other four wheel drive with open differentials. When we first got the '42 GPW I actually had to jack both ends up and spin the tires to satisfy myself that there wasn't any locker or limited slip in those differentials. Many times we have been amazed to find all four wheels spinning on what looks like fairly uneven ground. How is this possible?
Articulation is part of it, the suspension on the old Jeeps is able to move better than on many newer 4x4 vehicles. That's only one little part of it though, as many other softly sprung leaf spring 4x4 vehicles don't go quite as well over uneven terrain. Another part of it is that the smaller size makes it easier to pick lines that keep all four wheels evenly loaded, and I have found that I have gotten pretty good at this sort of line selection. Again that doesn't seem to be the entire explanation, as it is often possible to pick similarly effective lines with slightly larger vehicles.
While I was overhauling the Jeep in 2013 I found part of the rest of the explanation. The front differential is worn in a very peculiar way. It looks like the spider gears are severely worn, but close inspection reveals that they actually had a unique shape when new. The spider gears have an exaggerated almond shape, and they engage rather far out towards the ends of the gears. The result of this is a bit of a limited slip effect. The more torque is applied to these radical almond shaped spider gears the more they tend to jam together and not rotate. Just like a clutch type limited slip. Essentially the front differential is working like a very weak limited slip differential. It is hardly noticeable, but it does provide some additional grip on uneven terrain. Hardly noticeable, but not entirely un-noticeable either. It is part of why the CV joints pop and clank so much and why the steering effort increases noticeably in four wheel drive.
Overall the flat fender Jeeps are fairly competent little vehicles. The radical engine setback moves the weight of the engine, transmission and transfer case back towards the center of the vehicle, and that's really rather significant considering how heavy these big chunks of cast iron are compared to the rather light overall weight of the Jeep. Of course the small amount of overhang front and rear is a big part of what any Jeep is also. Less overhang not only improves approach and departure angles in extreme terrain, but it also just generally helps out with maneuverability. The Jeep is a very easy vehicle to use in a wide variety of conditions.
The lack of a low first gear in high range and the lack of enough of a top gear in low range can be annoying, but the close ratios do serve a purpose. Especially considering that the long stroke length engine tends to run over only very limed ranges of engine speeds it is useful to have rather tight spacing between the gears. Clearly a five speed would be better, but for a three speed the Jeep transmission works fairly well. In a sense it is sort of like a five speed. First gear in low range is first, then second gear in low range and first gear in high range are close to each other and are both like second gear, then third gear in low range is third gear, second gear in high range is fourth gear and high gear in high range is fifth gear. The annoying thing is just that it usually requires bringing the Jeep to a full stop to get between ranges. It is actually possible to get from low range to high range while driving along at lower speeds, but going the other way is pretty much totally impossible. It does really require coming to a full stop to get into low range.
As far as traction there is also something to a low cylinder count and long stroke length. For most situations it is just more power, more acceleration and more suspension that gets a Jeep up difficult climbs. When going slowly over somewhat loose terrain though often the best technique is to just back off on the throttle when the tires begin to slip. In this sort of a marginal traction situation the pulsation of the power delivery is significant. It's not so much that the pulsation is actually beneficial, as some people have claimed. Rather it is that the rate and shape of the power pulses does have some effect on traction. The ideal rate of pulsation appears to be approximately 25 to 30 per second, and that would tend to mean that a four cylinder engine would do better and better the slower it was capable of spinning. A lower 30 per second rate of pulsation may under some circumstances allow enough time for small rocks, pebbles and dirt to settle under the tires, where a faster rate of pulsation just keeps it all rolling and flowing. A long stroke length four cylinder engine then would seem to be able to get better traction than a shorter stroke length four cylinder engine. And this does sometimes seem to be true. There are however other dynamics that can also make lower engine speeds appear to work better under some conditions.
Sometimes it is just the gyroscopic effect of a large engine spinning fast that is problematic. Less gyroscopic effect means that the vehicle is more easily able to tilt so that the tires can follow rough terrain with a more even and constant contact force.
This can actually go either way in terms of whether a longer or shorter stroke length appears to work better. Since all gasoline engines of any stroke length tend to have to spin up to more than about 3,000RPM to make torque it actually ends up being a smaller, shorter stroke length engine that can run with less gyroscopic effect. A big engine spinning to 3,000RPM obviously tends to have more gyroscopic effect than a small engine spinning to 3,000RPM. It can go the other way though also. If the displacement is large enough to deliver sufficient power in full flame front travel mode then engine speed can be proportional to stroke length and long stroke length engines can spin more slowly. Large long stroke length engines do have a tendency to more reliably be able to run in full flame front travel mode simply because all of the engine development and tuning tends to be biased in that direction. For shorter stroke length engines performance in full flame front travel mode tends to be of secondary importance since they work so spectacularly better up above about 3,000RPM.
The reality is that there is even more to the dynamics of traction and power delivery, and ultimately it is the shape and duration of the power pulses that ends up being most significant. An engine running extremely harshly delivers short and steep torque spikes, and that's not good for traction. Interestingly though short duration power pulses can also be caused by excessively high mean piston speeds for the operating conditions. Keeping the duty cycle of the power pulses up under light loads requires lower mean piston speeds. Full flame front travel mode operation also always favors very low mean piston speeds, so the net effect is that it is incredibly easy for an engine to end up needing to spin more slowly to support light loads in full flame front travel mode.
Both of these ideas can also be expressed by saying that an engine running at low efficiency tends to have shorter duration power pulses that act to compromise drive traction. This is true both for excessive harshness and for excessively high mean piston speeds under very light loads. If the engine is running inefficiently then the torque output gets concentrated over a short duration of crankshaft rotation, and that means less drive traction.
The most obvious and immediately apparent manifestation of this is that detonation at any engine speed bellow 2,000RPM drastically decreases forward thrust. Very harsh operation at higher engine speeds caused by excessive spark advance and/or excessively low compression ratios tends to cause a similar, but less dramatic, loss of drive.
Under very light loads is where excessive mean piston speeds cause a loss of drive traction. When slippery conditions or a drastically oversized engine causes very light load operation getting traction often seems to require extremely low mean piston speeds. Full flame front travel mode always favors rather low mean piston speeds, and very light loads favor even lower mean piston speeds. If the mean piston speed isn't low enough for the conditions then the engine runs inefficiently, and the resulting narrowing of the power pulse duration compromises drive traction. This certainly is part of why long stroke length engines appear to need to idle way down low to get best possible traction in very slippery conditions. The longer the stroke length the lower the engine has to go, and also the lower the temperature of combustion potential of the gasoline the lower the mean piston speeds need to be.
After the 4-3/8" stroke length Willies engine in my Jeep started detonating bad at 1,600 to 2,000RPM last year I noticed that shifting to high range was required to slowly back up my gravel driveway in two wheel drive. In the past I was able to just rev the engine up a bit in low range two wheel drive and pull up the hill without much difficulty. Then after the detonation at 1,600 to 2,000RPM showed up in the summer of 2016 the Jeep seemed to refuse to back up that hill in two wheel drive. At first I didn't know what was going on, but I did find that it wasn't necessary to get out and lock the hubs or even to go faster up the hill. It just needed the higher gear ratio and lower engine speed of high range at roughly the same vehicle speed to keep the tires hooked up.
Another example of how this plays out is what I have observed with driving both diesel and gasoline powered Audi cars in mud and snow. All of the four and five cylinder diesel and gasoline Audi cars from 1981 through 1988 have exactly the same 3.4" stroke length, although the comparisons would tend to work out much the same even if the diesel engines had longer stroke lengths.
What I have observed is that usually it's the larger power output of the gasoline engines that delivers better hill climbing ability. In very slippery low speed conditions though the type of power delivery is significant. The worst thing for traction and hill climbing is a torque converter, both in diesel and gasoline cars. The torque converters are worse in all conditions. The torque converter means less power to the wheels, and that results in worse performance blasting up slippery hills. At lower speeds in slicker conditions also the torque converters are worse, but the reasons for this are a bit harder to figure out. What it comes down to is that it is more difficult to precisely meter out small amounts of power with a torque converter. This seems somewhat backwards since torque converters are so good at seamlessly delivering larger amounts of power accelerating through the gears. At low speeds in slippery conditions though the torque converter creates a disconnected feeling where it is hard to predict just how much torque is going to be delivered to the wheels.
As far as quality of power delivery in slippery conditions, the gasoline powered Audi cars usually seemed better than the diesel powered Audi cars. This however isn't necessarily a clear cut ruling in favor of gasoline power. When moderate amounts of power were required over wide ranges of engine speeds the turbo diesel powered Audi 5000 with a manual transmission seemed to do very well. Especially when the engine speeds tended to fall in the 1,800 to 3,000RPM range the 3.4 inch stroke length 2.0TD turbo diesel was able to meter out good strong and well modulated torque.
When smaller amounts of power were required in very slippery conditions though the five cylinder 2.2 liter gasoline engine on a manual transmission did dramatically better than the diesel engines. Backing off on the throttle and letting the 3.4 inch stroke length fully mechanically controlled CIS injected gasoline engine chug along at 1,500 to 1,800RPM or even way down to 1,200RPM under very light loads in second and third gears delivered spectacular drive traction in the slipperiest and snottiest mud and snow conditions. The early 1980's Audi gasoline engines use fully mechanical injection systems, and although the advance curve is provided by an electronic control box it is functionally the same as a centrifical advance because it doesn't use a throttle position sensor or any other inputs. It's just an advance curve.
The way the fully mechanically controlled CIS injected 8.2:1 2.2 liter Audi five cylinder gasoline engine ran back in the 1990's was that it was only smooth with just the right small throttle openings. Torque was respectable at around 1,500 to 2,000RPM and very smooth as long as the correct throttle position was used. Torque dropped off significantly as the engine speed was reduced from 2,000 to 1,500RPM. Then the torque dropped off even more dramatically bellow 1,500RPM, but there was still spectacular drive traction available down lower under very light loads. At wider throttle openings it just got very harsh without making more torque. Even at wide throttle openings though there wasn't usually any pinging anywhere from 1,000 to 1,800RPM. It did usually sound very bad at wide throttle openings everywhere bellow 3,000RPM, but feathering the throttle just right there was a respectable amount of very smooth torque available. Even up to 3,500 and 4,000RPM the fully mechanically controlled CIS port injected Audi five cylinder didn't seem to want to take full throttle. It ran fairly well at substantial part throttle openings, but wide open up as high as 4,000RPM it got harsh without making significantly more torque. The torque everywhere from 1,500 to 2,500RPM was quite strong compared to most other automotive gasoline engines of the same size, no doubt due to the under square configuration with small 79.5mm bores. There was always power available to 6,000RPM from the Audi five cylinder, but there was usually pretty severe harsh vibration above 4,500RPM. Torque at 3,000 to 3,500RPM seemed a bit weak compared to many EFI port injected automotive engines of the same size, but power did continue to build significantly to 4,500RPM. The power increased quite a bit from 3,000 up to 3,500 and from 3,500 up to 4,000RPM, but then it was a smaller increase from 4,000 to 4,500RPM. Above 4,500RPM it was just very flat out to 5,500 and 6,000RPM with severe harsh vibration building from 4,000 and continuing all the way out past 5,000RPM.
As far as delivering big power the main problem with the fully mechanically controlled CIS port injected engine was that it only seemed to want to run over an extremely narrow range of engine speeds right around 4,000 to 4,500RPM. At lower engine speeds it wouldn't take wide open throttle, and then above 4,500RPM it just went extremely flat with horrible sounding violent harsh vibration. It only seemed to want to run right at 4,000RPM. It did get fairly good gas mileage under light loads though, delivering 30mpg at 3,300 to 3,500RPM sustained cruising speeds on the freeway. The output rating of the 1976 through 1984 fully mechanically controlled CIS injected 2144cc five cylinder Audi engine was 100, 103hp or 105hp at 5,100 or 5,500RPM, with peak torque variously listed as 122 foot pounds at 4,000RPM or 112 foot pounds at 3,000RPM. That 122 foot pounds of torque at 4,000RPM is 93hp. Even from the ratings it can be seen that this engine goes very flat above about 4,500RPM. There was also a 1982 through 1984 European only normally aspirated 9.3:1 version of the 2144cc five cylinder that was rated at 129 or 134hp at 5,900RPM and 126 foot pounds of torque at 4,800RPM with a bigger 230 degree at 1mm valve lift camshaft with a 110 degree lobe center. The valve sizes on all of these 2144cc engines is 38mm on the intake and 33mm on the exhaust, which is a bit on the small size for the 79.5mm bores even with the parallel valve configuration. Especially on the intake valve that's rather small, which is right inline with it having been designed primarily as a forced induction race engine.
When the electronically controlled CIS-E engine management system was introduced for the 1984 or 1985 model year the five cylinder Audi engine was punched out to 2226cc with a slightly larger 81mm bore, again with the same 38mm and 33mm valves though. The compression ratio was also increased to 8.5:1, which is exactly the increase that going up from 79.5mm bores to 81mm bores with the same compression height pistons, the same deck height, the same rod length, the same stroke length and the same cylinder head would yield. This modern electronically controlled 3.4 inch stroke length 136 cubic inch Audi engine was rated at 110 or 113hp at 5,500RPM and 126 foot pounds of torque way down at 3,000RPM.
In the very low engine speed slippery conditions the metering collar equipped Audi diesel engine was harsh and stubbornly refused to hook up. With a fixed injection flow rate set for big power at high engine speeds the old 1980's Audi diesels didn't do well under extreme light loads. Interestingly the IDI combustion system and large in head pre-combustion chambers makes this problem worse. The restrictive openings between the pre-combustion chambers and the main combustion chamber tends to require an even higher injection flow rate to deliver power at high engine speeds, and that means worse operation under light loads at low engine speeds.
The early 1980's Audi cars in general do better off-road and in slippery conditions compared to other front wheel drive cars for a couple of different reasons. One obviously is that the big heavy iron block five cylinder engine hanging off the front puts a lot of weight on the drive wheels. They are also very light weight cars for their size. Another factor is the suspension. The smooth long travel suspension tends to follow the terrain well, and that increases drive traction.
Twice now in 2017 I have tried completely draining the gas tank on my Willies powered 1942 Ford GPW Jeep and refilling it with fresh gasoline straight from the gas station. Both times the results have been the same; horrible detonation and a near total lack of torque from 1,600 to 2,000RPM.
The first time I drained the tank was back in January of 2017, and I refilled it with 3.5 gallons of 87 (RON+MON)/2 octane rating regular gasoline. On that evening with the fresh regular gasoline straight from the gas station I was able to get a bit of a throttle opening up to 1,800RPM without detonation, but there still wasn't any torque. Just a complete lack of torque everywhere from 1,600 to 2,000RPM, and then horrible sounding harsh operation with still hardly any torque at 2,000RPM and slightly above. The torque did increase as the engine speed was increased, and around 2,500 to 3,500RPM it seemed about normal for the long stroke length 134 cubic inch engine. It was however done very quickly, and 3,500RPM seemed like the absolute top end. Revving past 3,500RPM it was just weak and lean with some cutting out and stumbling. This is nothing like the smooth and fairly strong torque everywhere from 1,300 to 2,000RPM that I was used to from this engine before the summer of 2016.
I then tried a gallon of the same fresh 87 (RON+MON)/2 octane rating regular in my 9.7:1 386 stroker motor on the same day, and it didn't work. Horrible surging around 5,000 to 6,000RPM, a severe lack of torque and the engine wouldn't rev up anywhere near like it usually does. It was so bad that I just drained what was left of that gallon of gasoline out of the tank on the 1991 Husqvarna WMX 386.
Then in early July of 2017 I again completely drained the tank on the Jeep. This time I refilled it with fresh 91 (RON+MON)/2 octane rating premium gasoline straight from the gas station, and the results were much the same; horrible detonation and a near total lack of torque from 1,600 to 2,000RPM. It was a bit different though as the gasoline was even weaker with worse lean stumbling. The 134 cubic inch Willies engine was still idling along fairly well everywhere from 1,000 to 1,600RPM at all throttle openings. I was able o get up to about 1,750RPM with small throttle openings, but the torque was practically non-existent. Then above 1,800RPM the engine wouldn't take much of a throttle opening at all without detonation. The detonation seemed extremely bad at 1,800 to 2,000RPM, but then above 2,000RPM it smoothed out amazingly quickly. Torque was still weak, but by 2,300RPM it seemed actually sort of usable. The torque stayed very flat from 2,300 up to about 3,000RPM. It got smoother and smoother as the engine speed was increased above 2,300RPM, but the torque didn't increase. Then right at 3,000RPM there was a big increase in torque and some power was available over an excruciatingly narrow range of engine speeds from 3,000 to 3,500RPM. That power at 3,000 to 3,500RPM seemed weaker than usual for the Willies engine, and then above 3,500RPM nothing. The power just stopped at 3,500RPM and there was lean stumbling. On this fresh premium there was even some lean stumbling sometimes around 2,000 to 2,500RPM at wider throttle openings. If I opened the throttle too quickly past 2,000RPM it would cut out momentarily around half throttle before taking off again and continuing to pull. Basically the engine wouldn't run at all. The gasoline was just too weak and too lean. All it would do was idle along at 1,000 to 1,750RPM. It was able to take wide throttle openings up to 1,600RPM, but torque is always rather weak down bellow 1,300RPM so there just wasn't much power to be had. Then if I tried to open the throttle wide at 1,600RPM it just started detonating. I could only get to 1,750RPM with small throttle openings, so there wasn't any substantial torque anywhere from 1,000 to 2,000RPM. Even though the torque increased rapidly past 2,000RPM it sounded so harsh and horrible that those engine speeds from 2,000 to 2,300RPM seemed just totally unusable. Only above 2,300RPM did it smooth out enough to seem usable, but even then there wasn't much torque. Substantial torque was only available above 3,000RPM, and even at 3,000 to 3,500RPM it was less power than is usual for this Willies engine. Basically just totally useless.
I had bought 4.5 gallons of that fresh premium, and on the test ride in the Jeep I had carried the remaining two and a half gallons in the five gallon gas can I had taken to the gas station. When I was done with the Jeep test ride I put that two and a half gallons into the empty tank on my 1991 Husqvarna WMX 386. First I drained the gallon and a half of old gasoline that had been in the bike, and then I filled the tank up with the fresh premium straight from the gas station.
I then took the 1991 Husqvarna WMX 386 out for a substantial little test ride. The 9.7:1 386 stroker motor seemed to be running fine at small throttle openings, and it was extremely crisp. Torque was totally instant everywhere from 3,000 to 4,500RPM, but it got harsh very quickly at 3,000 to 4,000RPM at wider throttle openings. It was obviously running extremely overly crisp. When I revved the engine out though it was reluctant to make power, and the power ended very early at 8,000RPM. The 2.68" stroke length engine was seeming to run fine at 4,300RPM, but then at 4,800RPM it seemed very reluctant to rev higher. It was like it was hitting a wall at 5,000RPM and just didn't want to make power. With a big twist of the throttle though it did get going at 5,000RPM, and then there was quite a bit of bad surging from 4,500 to 5,500RPM once it did get going. The 2.68" stroke length engine was requiring extremely early times of late compression ignition to make power above 5,000RPM, and this was causing quite a bit of bad surging.
The 386 stroker motor did continue to rev higher and make more power, but it was a bit weaker than usual and the power ended extremely early. The power was sort of respectable around 5,500 to 6,000RPM and then it was a bit flat from 6,500 to 7,000RPM before taking off and making considerably more power from 7,000 to 7,500RPM. Then again it went flat from 7,700 to 8,000RPM and wouldn't pull past 8,000RPM. There were also the beginnings of some rhythmic surging around 6,700 to 7,000RPM, a sure sign of extremely low temperature of combustion potential gasoline in the 2.68" stroke length engine. What really defines this extremely weak gasoline though is that despite the huge levels of excessive crispness it just wouldn't pull past 8,000RPM. The 386 stroker motor normally makes it's strongest power in the 8,000 to 9,000RPM range of engine speeds, and that power usually continues up to around 9,500RPM with little difficulty when pressed. The power completely ending way down at 8,000RPM is just ridiculous for this engine, it just doesn't run that way.
I headed up to higher elevation to see what would happen with the extreme levels of excessive crispness on this weak gasoline. Sure enough the 9.7:1 386 stroker motor ran better as I climbed up to 3,000 and 4,000 feet of elevation. Right away the engine sounded better at 3,000 to 4,000RPM, and torque actually seemed to increase very slightly up to 4,000 feet of elevation. At 4,000 feet of elevation the engine was still willingly pulling up to higher engine speeds, but as I climbed above 4,000 feet of elevation the engine very quickly became reluctant to get going above 5,000RPM. Up to 5,000 feet of elevation I was still able to get about the same amount of power up to 7,000RPM, but the engine needed to be fully warmed up on some big pulls to reliably delivery the power. The engine also remained extremely crisp everywhere from 3,000 to 4,000RPM, with instant torque each time the throttle was twisted.
All the way up to over 6,000 feet of elevation I was still able to get power to 6,700RPM, but only once the engine was well warmed up from some big pulling and there was lots of reluctance to get going everywhere above 5,000RPM. Again though the engine was still pretty crisp at 3,000 to about 4,500RPM as long as it remained hot from big aggressive pulling. When I cruised and coasted along up at 6,000 feet of elevation for a while the engine cooled off and then wasn't so crisp down low. Instead of instant and somewhat harsh torque at the first twist of the throttle at 2,700 to 3,000RPM as it had been down lower it was instead just full flame front travel mode operation all the way up to 3,500RPM. Then the late compression ignition hit and the torque increased all of a sudden right at 3,500RPM.
When I dropped back down to 5,000 feet of elevation the instant torque was available down to 3,200RPM, but from 2,700 to 3,200RPM it was still just very smooth full flame front travel mode operation. The hit of torque at 3,200RPM was still rather smooth though. Unbelievably smooth for that low 3,200RPM engine speed really. Only once it was popping off on late compression ignition down bellow 3,000RPM was there any noticeable undue harshness.
One important thing that climbing up to over 6,000 feet of elevation had demonstrated was just how the engine ran in full flame front travel mode versus in late compression ignition mode around 2,700 to 3,500RPM on this very weak gasoline. There was a bit more torque available at 2,700 to 3,000RPM in late compression ignition mode than in full flame front travel mode, but for the most part there didn't seem to be much need for late compression ignition bellow 3,000RPM. The abrupt end of the power at 8,000RPM might seem to indicate slow flame front travel speed gasoline, but this wasn't really true. There wasn't any hard cutting out at 8,000RPM, instead the power just dropped off substantially without anything dramatic happening. This was in fact at least moderately fast flame front travel speed gasoline. Even with hardly more than 20 degree BTDC spark timing the 2.68" stroke length engine had been running really just about as strong in full flame front travel mode as in late compression ignition mode up to about 2,800RPM. Interestingly 2,800RPM in the 2.68" stroke length 386 stroker motor is the same mean piston speed as 1,700RPM in the 4-3/8" stroke length Willies Jeep engine. The much shorter 2.68" stroke length 386 stroker motor unsurprisingly had a much easier time transitioning from full flame front travel mode to late compression ignition mode around 2,800 to 3,200RPM than the big 4-3/8" stroke length Willies engine did at 1,700 to 2,000RPM. The 2.68" stroke length 386 stroker motor was easily able to run in either full flame front travel mode or late compression ignition everywhere from 2,600 to 3,500RPM, where the big 4-3/8" stroke length Willies Jeep engine only worked in full flame front travel mode up to about 1,750RPM and only worked in late compression ignition mode down to about 2,300RPM. The 2.68" stroke length 386 stroker motor had a substantial overlap where either full flame front travel mode or late compression ignition mode worked well, where the big 4-3/8" stroke length Willies engine had a substantial gap from 1,750 to about 2,200RPM where neither full flame front travel mode or late compression ignition mode would work at all.
Another interesting thing was that the transition from the latest possible time of late compression ignition to the earlier and easier to hit time of late compression ignition was causing a big increase in torque around 3,000RPM in the 4-3/8" Willies motor, where I could hardly find that transition on the 2.68" 386 stroker motor running the same gasoline. It was obviously the latest possible time of late compression ignition that was delivering such smooth torque from 3,000 to 3,800RPM, and it was obviously earlier times of late compression ignition up at 4,300 to 4,800RPM just before the severe surging came on. The transition wasn't always taking place at the same engine speed. Down at low elevation the engine was just tending to get very harsh everywhere around 3,000 to 3,700RPM with anything other than very small twists of the throttle, but amazingly and unexpectedly this extreme excess crispness and harshness wasn't causing all that much drop in torque production until the engine speed was way down under about 3,300RPM. Then up at 5,000 feet of elevation it was just all incredibly smooth operation all the way through from 3,000 to 4,800RPM just before the surging set in at 5,000RPM. I did notice that up at 5,000 feet the smooth torque at around 4,000 to 4,800RPM did increase a bit when I got the engine well warmed up with some big pulls, so that must have been the range of engine speeds where the time of late compression ignition was becoming earlier and earlier but not yet getting pushed way over to the BTDC times of late compression ignition that cause severe surging.
The point is that the shorter stroke length both substantially smoothed the transition from full flame front travel mode to late compression ignition as well as substantially smoothing the sharp transition from the latest possible time of late compression ignition over to the earlier and easier to hit time of late compression ignition. Clearly the 4-3/8" stroke length was dramatically too long.
When I dropped all the way back down to 1,000 feet of elevation the 9.7:1 386 stroker motor at first ran better than it had all day, with more instant torque and less excess crispness at 3,000 to 4,000RPM. At first I thought the spark timing had slipped down, but it turned out to have just been that the engine cooled off a lot in cruising down from high elevation. As soon as I got the engine warmed back up the extreme levels of excess crispness at 3,000 to 4,000RPM were back as bad as ever, and so was the surging at 4,500 to 6,000RPM and the 8,000RPM abrupt end to power delivery.
When I got back I checked the static timing setting, which I found to be at the same 23 degrees BTDC where I have been running the 9.7:1 386 stroker motor. I also filled the tank to check the gas mileage. It took 1.6 gallons after a 60 mile ride. Wow, that is a very low 38mpg! It was 1.8 hours on the hour meter, so the average speed was 33mph. Pretty typical of a mixed ride mostly on larger dirt roads and small paved roads. The 386 stroker motor usually gets around 50 to 55mpg on that type of ride with lots moderate speed cruising in sixth gear. Usually it is only extreme levels of hesitation that can cause the mileage to drop bellow 45mpg on the 386 stroker motor, so that 38mpg while the engine was running very crisply with instant torque was just very unexpected. Surging poor power delivery, a severe lack of top end power and very low gas mileage. That all adds up to unusually weak gasoline. Really spectacularly weak gasoline actually. So weak that it basically wouldn't work at all in the long stroke length Willies Jeep engine.
So the question remains: What is normal gasoline? Is it the more powerful pump gas that pulls hard everywhere from 3,500 to 8,500RPM in the three inch stroke length Husqvarna 610 motor without surging and also pulls hard to around 9,200 or 9,500RPM in the 2.68" stroke length 386 stroker motor without surging? Or is normal gasoline supposed to be the much weaker and seemingly watered down garbage gasoline that surges horribly around 4,500 to 5,500RPM in the three inch stroke length 610 motor and surges horribly at around 5,000 to 6,000RPM in the 2.68" stroke length 386 stroker motor without power above 8,000RPM? Which is it? They are both dramatically weaker than the race gas style pump gas that has also sometimes been common, the very high pressure gasoline that absolutely needs a compression ratio above 11:1 to run well yet can also support fairly big torque to 3,500RPM in three and a half inch stroke length automotive engines running only in full flame front travel mode.
A lot of people seem to think that normal gasoline is that race gas style high pressure gasoline that only works above 11:1 compression ratios. When this very high pressure gasoline persistently comes out of the pumps as gasoline then obviously people are going to think that it is normal gasoline. I don't have any real information on the subject, but that very high pressure and very powerful gasoline is probably race gas not normal gasoline.
Most evidence seems to point to the surge free power peaking at or just before 8,500RPM in the three inch stroke length Husqvarna 610 motor as normal gasoline. This would be the gasoline that a worked out 383 cubic inch 3.75" stroke length 10.5:1 small block Chevy makes peak torque of 500 foot pounds at around 5,000RPM on and can pull hard to 6,500RPM on the same dyno run with an aggressive roller camshaft and special lightweight valve train parts. It's also the gasoline that the 2016/2017 Ford Mustang Shelby GT350R needs to deliver it's rated 429 foot pounds of torque and 526hp at 7,500RPM from the port injected, normally aspirated 3.66" stroke length 5.2 liter (315 cu in) DOHC roller follower Coyote V8. The Coyote seems to deliver a whole lot more top end performance than a traditional small block Chevy, but four valves per cylinder and a lightweight roller valvetrain makes a big difference.
This would also be the gasoline that a stock (but not cam and bucket) 2.5" stroke length 450F dirt bike pulls hard from 6,000 to 11,000RPM on, with peak power somewhere around 9,500RPM. It's also the gasoline that reliably delivers detonation free smooth torque at 1,800 to 2,800RPM in 3.5" stroke length port injected automotive gasoline engines. This very well may be the most powerful and hottest burning gasoline that can be produced with a reasonably high refining efficiency. This might be normal gasoline. But, then again I don't actually have any direct evidence for what normal gasoline really is.
Could it be that it is the dramatically lower temperature of combustion potential gasoline that works so poorly in long stroke length engines is actually the correct high refining efficiency normal gasoline? Perhaps. Could it be that a 2.68" stroke length is simply too long for normal gasoline? Perhaps. Down at 2,500 to 4,500RPM the 2.68" stroke length 386 stroker motor runs on the dramatically lower temperature of combustion potential gasoline much like a 3.5" stroke length engine does on what has been considered normal gasoline. Late compression ignition, even at the latest possible time with spark timing of 23 degrees BTDC or later, is rather harsh down at 2,600 to 3,000RPM but can deliver some usable torque. Then above 3,200RPM late compression ignition is very smooth and quite powerful, but the stroke length is so excessively long that very quickly earlier times of late compression ignition are required to support higher mean piston speeds. This can still sort of work up to about 4,500RPM. Up to around 4,000RPM the latest possible time of late compression ignition provides fairly strong smooth torque, but then at higher mean piston speeds earlier times of late compression ignition are quickly required. This continues to sort of work as long as the times of late compression ignition remain ATDC. If huge amounts of crispness are not provided to knock the time of late compression ignition over to the before top dead center side then the long stroke length engine just goes very flat as engine speeds are increased above about 5,000RPM. Then if the ridiculously earlier times of late compression ignition are attained at 5,000 to 7,000RPM it results in surging and difficult to control poor power delivery.
If that dramatically lower temperature of combustion potential gasoline is in fact normal gasoline then the maximum practical stroke length is about 2-1/2 inches, and even at that much shorter stroke lengths would deliver much higher operational efficiency.
Something to keep in mind is that three and a half is actually substantially closer to four and three eights than it is to two and a half.