Long stroke, short stroke. More than you want to know

[George Miller]

Long stroke was good for getting the car through the muddy roads in the old days. It is also good for tractors and trucks that pull heavy loads up hills or pulling a plow.

Short stroke is good for a higher RPM range. Other words the engine is more flexible for using in a car now days.

Most of you are to young to remember this, in 1955 when Chev came out with there short stroke 265 it 3=3/4 bore and 3 inch stroke. We could not believe how fast they were. They would 6000 rpms from the factory. I would not try that with a stroked Model A .

Yes I have turned a stock stroke Model A to 5000 rpms at a hill climb, but it had my home built over head on it. I was not worried about it lasting a long time. Funny thing it broke valve lifter and I still had the fasts time of the day.

[bambooboy]

George,I think there are more here that do remember than not.my 54 ford v8 could never keep up with the 55and56 265 chevy. Tom

[2manycars]

Whne the Ford flathead V8 came out, Henry said "long stroke for power, small bore for fuel economy, and 8 cylinders for smoothness". The power he spoke of was torque, for quick acceleration (to a point). My Harley has a long stroke, and has torque up the wazzoo, but my 750 honda with a short stroke will wind up to amazing rpm, and leave the harley in the dust.

[WestCoast]

long stroke equals torque, low end power, short stroke equals high rpm and horse power which equals speed

[mshmodela]

Long stroke is like a steam train engine... Just more fun getting them up to speed...

[Y-Blockhead]

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Originally Posted by bambooboy

George,I think there are more here that do remember than not.my 54 ford v8 could never keep up with the 55and56 265 chevy. Tom

FYI... Your '54 Ford was only 239 In3 and admittedly not designed to go fast. Ford changed the design of the Y-Block in '55. Not many parts interchange between '54 and the later Y-Blocks.

[40 Deluxe]

Don't forget that more than stroke length is involved in the low RPM vs. high RPM comparison. Displacement, valve timing, compression, valve and port size, carburetor size, combustion chamber design, exhaust manifold and pipe design and size (for scavenging), and more all play a big part.
Food for thought: Put any engine of any type on a dyno and the only output you can measure is torque! Peak torque is produced at the RPM at which the engine is most efficient. "Horsepower" on the other hand is never measured! It has to be calculated from the torque measurement using a standard formula: Horsepower equals Torque times RPM divided by the Constant 5252. (Which is why a horsepower/torque chart always has the torque and horsepower curves crossing at 5252 RPM, no matter what kind of engine.) It's fun to play with this formula. Figure the horsepower for an engine that has peak torque of 200 ft. lbs. at 1,000 RPM, then figure the same 200 ft. lbs. at 6,000 RPM and see the difference in horsepower! It goes from 38 HP to 228 HP with identical peak torque numbers; just by raising the RPM.

[40 Deluxe]

Well, obviously you have to first rev the engine to at least 5252 RPM! What's so difficult about that??

[40 Deluxe]

Originally Posted by 40 Deluxe

Well, obviously you have to first rev the engine to at least 5252 RPM! What's so difficult about that??

OK, looks like you got me on that. Guess I have to go back and read older books!

[Chris in CT]

Hey 40 D and Forever, You might not actually be so far apart. Four times 1400 equals 5600, or, 5252 divided by 4 equals 1313. Given some room for inharmonicity, 1400 rpm could be a sub-tonic for > 5252, or 5252 could be the fourth partial for <1400. One would have to project the chart for a Model A engine capable of 6000 rpm, and I do not have the math for being able to project that onto a graph, or any other piece of paper, either.
Just sayin', you might not be so far apart... Happy Torquing!

[Sparky]

Originally Posted by 40 Deluxe

Well, obviously you have to first rev the engine to at least 5252 RPM! What's so difficult about that??

Mathematically, that's correct, you can see the torque and HP curves heading towards an intersection point if it could rev that high. However the equations don't say they can't cross at other points, as seen on the chart. Most modern engines don't produce any useful torque at 600 rpm!

[Rex_A_Lott]

Even though they are on the same graph here, the scales are not the same. Torque is on the right on this one, and doesnt match the HP scale.
On the modern graphs we are used to looking at the x and y axis are the same for both and they all do cross at 5252.

[Sparky]

Good point, Ford probably did that for convenience since the HP numbers are low.

Another quirk: the units for torque are shown as lbs./ft. which is incorrect; it should be lb-ft.

[George Miller]

Let me say I'm all for what any one wants to do to there engine. That is how we learn. But when ask a question I'm going to give the best answer I can.

To show how craze I am, here is a Model A engine that I have been working on. It will be 3=1/2 inch stroke, 4 inch bore, and 5 mains. full pressure And will have my home made over head on it. I'm looking for 150 hp or more.

Will I ever get it done I hope so. Will it work out, don't know but that is part of the fun.

[Chris in CT]

Vince, Geesh! I think I need a cold shower... oooh! C.

[hardtimes]

Ha, never heard IT stated so simply and succinctly !!

BTW George,
You do nice work !

[Bill Stipe]

George!! what's that Chevy crap doing in a Ford you know we had to bale out GM right. LOL good luck with getting it done. by the way I sold my WI house last week so I will be an official Kentuckyen January 1.

[George Miller]

Hi Bill I wanted to use one of your cams but they will not work with my firing order. now you are closer maybe we can get together some time.

[MrTube]

Overall, I agree with Mr Miller.

It's amazing how many times I see guys say torque is power.
Torque is torque just as rpm is rpm. You can't have power without both. Torque is NOT power. Watts is power, so is horsepower, btus and calories. An engine producing 50 foot pounds @ 5000 rpm is just as strong as one producing 100 foot pounds @ 2500 rpm, there is no difference in power.



Larger bore breaths better so Henry was right, small bore for good fuel economy but who wants a suffocated large heavy engine?


Engines that peak their horsepower above 5252 rpm will always have higher horsepower than torque. Engines peaking horsepower below 5252 will always have higher torque numbers than horsepower. Never heard of anyone trying to cross anything though?

What I feel is most important for a general use engine is a good wide power band. So far, the GM 1.4 turbo have by far, been my favorite engine for a daily driver. Ford and other companies have similar products as well. Torque peaks just below 1900 rpm and it holds it until almost 5000 rpm. Excellent for normal driving and it cruises smooth and happy at 1400 rpm.

I've attached the power curve.

[George Miller]

Originally Posted by Bill Stipe

George!! what's that Chevy crap doing in a Ford you know we had to bale out GM right. LOL good luck with getting it done. by the way I sold my WI house last week so I will be an official Kentuckyen January 1.

Bill I seem to remember you cutting a chev V8 head into and welding it back together for one of your A engines. Was that before you found out Chevs we crap. Or did I remember wrong. Good luck with the move.