The Stovebolt Site Forums The Shop Area The HiPo Shop Short stroke- - - -high RPM stovebolts?

Back in the dark ages when I was growing up around a dirt track racing shop, there was a sign on the wall- - - -"Build 'em little- - - - -wind 'em tight- - - -get the chemicals just right!" Dad was always looking for ways to turn those flathead Ford V8s considerably higher RPM than his competitors. While most of the other guys were running long stroke crankshafts in the pursuit of higher torque, Dad ran shorter strokes, bigger bore sizes, and turned his engines much higher RPM than his competition. He also won a lot of races. Everybody was running the same kind of fuel- - - - -alcohol, with a heavy dose of concentrated hydrogen Peroxide- - - -which produced more oxygen in the combustion chamber than Nitromethane. It also allowed compression ratios around 11:1.

Since stovebolt engines have such terrible intake and exhaust port shapes, which effectively limits the volume of air they're able to flow, I wonder why nobody has explored the possibility of small displacement engines running at higher RPM while staying within the flow capabilities of the less than ideal cylinder head design? A 216 engine has a 3.5 inch stroke. Why not drill a 216 crankshaft for full pressure oiling, destroke it to 3.25", and run that crankshaft in a 235 or 261 engine block? Less displacement, shorter stroke and a LOT more RPM! A stovebolt built that way would probably sound like a bumblebee on steroids! That would probably require stiffer valve springs, and maybe roller bearing rocker arms and/or valve lifters, but it could certainly surprise a few people! A standard bore 261 with a 3.25" stroke would have 215 cubic inches, and probably be capable of 6K+ RPM.
Jerry

Good concept Jerry, but I don't think it would be possible to drill a 216 crank for full pressure oiling. Because of the large lightening holes in the crank throws. Maybe if you have a flexible drill bit that can drill around corners. It would definitely take some pretty precise drilling if a straight line between main and rod journals could be found to miss those lightening holes (which 235 cranks don't have.)

Several places used to do that years ago, including one of the camshaft regrinders, so if they could figure it out using manual machine tools, a modern CNC shop could most likely do the same thing with a minimum of programming. It would also be possible to use a pressed-in piece of seamless tubing (like a small block V8 pushrod) to fabricate an oil gallery, staked or welded into place to keep it steady from centrifugal force. "Impossible" only means that somebody hasn't done it yet! I've got a bolt-on jig on the drawing board, one that would attach to a rod journal and guide a long drill bit with hardened steel drill bushings. Once a small diameter hole (maybe 1/8" or 3/16") is in the right position from the rod to main journal, it can be reamed or otherwise enlarged to make an oil passage.
Jerry

A piece of tubing pressed in across the lightening hole would work. Just another step to doing it. From the looks of the crank I have the hole would have to cross the lightening hole. I agree that there's always a way to do something. A little more head-scratching might be necessary. You're the guy who can figure it out Jerry.

I love building "sleepers"- - - - -engines that look completely original, and do stuff that seems to be impossible. The "305" claimer engines I used to build for circle track "street stock" class were beating guys with 350s- - - - -turning over 1K RPM faster consistently. We were limited to a 350 CFM Holley 7448 2 barrel carburetor, so building a destroked 305 with 100 cubic inches less to feed let my engines wind up impossibly tight. Yes, they were illegal (non-stock 2 7/8" stroke), but unless somebody paid a very expensive protest fee to tear the engine down, all my "305" casting numbers were correct. I just couldn't win a low RPM torque battle off the turns with a 350. Low rear end gears and lots of RPM made that a moot point. If my guy ever got to the front of the pack, the only thing the race would decide was who was going to finish second!
Jerry

Another example of a "big bore/short stroke" engine would be a 235 bored .060" oversize to 3 5/8 inches, with a 3.25" destroked 216 crankshaft- - - - -201 cubic inches, and a very high-winding RPM capability. With the right combination of properly weight matched lightweight pistons and rods, and smaller than standard rod and main bearings, the engine should be capable of continuous operation in the 4K to 5.5K RPM range. "A bumblebee on steroids!"
Jerry

Reminds me of the old arguments of 283 versus 350/383/400 smallblock Chevy. We had a Malibu that came with a 307 and when it smoked out (we're talking James Bond smokescreen here when you downshifted on the highway) Dad found a 283 somewhere and we installed it over a weekend.

I'll take that nimble little 283 over the frame flexing brute of a 396 any day. Even the fairly mild mouse motor could light up a lovely two tire fire.

How fast do you think a 3.50" crank can turn?
A reduction to 3.25" is about 7.7% faster, but where does 6,000 RPM come from?
Working backward from the above gives the 3.50" crank 5,600.

The 2 7/8" stroke 289 Fords that Red Farmer raced would turn 8K all day- - - - -and he did it for decades with dozens of engines. The only limiting factor on my 250 cubic inch "305" was a restrictive carburetor. RPM is simply determined by efficient airflow, proper cam profile, and plenty of valve spring. A circle track engine with 500 miles on it is about as rare as a chicken with lips- - - - -they wear out or blow up before then.
Jerry