The latest Hot Rod Magazine (June 2005) did an article on Bore vs Stroke by building two virtually identical BB engines with different bores and strokes. 4.560x3.766 vs 4.280x4.250 Peak and average power and torque were virtually the same. Some of you may want to pick up the article.

 

It would have been better to see the short stroke motor with long rods though.

 

Duh, torque and hp are not functions of stroke or bore, but of amount of air and fuel burned or engine size.

 

yeah that was a very informative article. i have always been curious to see what difference a longer rod would make. i am happy to see that there is not much...........

 

https://www.thirdgen.org/techbb2/sho...hreadid=295467

Interesting that with the big cam, the short stroke engine produced higher torque and at a lower RPM than the long stroke engine. A couple of years ago, there was an argument here that a 305 and 350 would produce the same torque, all other things being equal, because they have the same stroke. Riiiight. As ME says, it's how much air & fuel that's pumped through that makes the difference. However, larger bore tends to pump more air than longer stroke because of valve issues.

 

It would have been more interesting to compare a pair of similarly sized SBCs with the same displacement but different bore/stroke.

 

Its been done before by one of the mags. The same results were found.

 

Sorry about posting the same thing. I figured someone would post on it but I didn't see any when I looked.

 

Stealth subject line.

As for SBCs, the one I recall is 383 stroker vs. 377 destroker. They did taylor the package for each engine as I recall. They tended to verify the "conventional wisdom" with that "test".

 

Those are still relatively large bore blocks, I was thinking something more along the lines of something with a stroked 305 block which would help put all this 335 nonsense to rest.

 

That makes sense; I stopped subscribing years ago because the only "interesting" section was the Q&A in the back of the rag.

 

Actually thats a good idea. The problem though is that they need to know somebody thats building the motor for some reason. You could maybe do a bored 327 and a stroked 305 to get the same displacement. But know body is stupid enough to build a 335.

 

How about a 302 vs a 305? Similar displacements, radical different bore/stroke. Think we know how that will turn out huh.

 

Pretty much like the article....

I think if you quit holding on to your preconceptions and prejudices, and instead listen and read and learn something, you might find that alot of the crap you believe in (like the 302/305 thing) is completely mistaken, or at best, greatly exaggerated. And not just about cars either.

 

I also enjoyed reading the article, but.....

Why not tailor the camshaft to the engine package better? I think it is unfair to make both engines use the same components.

It would be fun to see a mag build a torque 383 and high winder 377 install them in identically prepped cars and shoot it out.

 

That wouldn't be a meaningful comparison either. You'd have to try both camshafts in both engines.

 

That was exactly CONTRARY TO THE POINT of the article. The point was to show how little of this "torque monster" and "high RPM" crap based on the short stroke vs. long stroke actually has basis in reality.

So one could say, it would also be fun to build the 2 combos exactly the opposite of the McDonald's Friday night monkey-spank; i.e. a 383 with a "high RPM" setup on top, and a 377 with a "torque monster" setup on it. Which would show even more graphically, how little the bore/stroke ratio has to do with the engine's optimum RPM range, and how in reality, once you get past the point of bore shrouding and up until the speed of sound becomes an issue (8,000 RPM or so), it's all determined by the induction system.

 

And why not a high torque 377 against a high winder 383?

EDIT: WOW!! I was a little late with that comment, wasn't I?

I guess I shouldn't let my wife interupt me when I'm talking about bored and stroked.

 

I might have looked at that same comment and never gave it much thought if it weren't in the same magazine issue as the straight six build up. The 292 Chevy straight six puts out good torque but it doesn't carry big displacement. Have to conclude it's the long stroke...right?

 

You can't conclude anything without something to compare it to.

 

Not sure I understand your comment. If I find an orange, I can see it's the color orange. I peel it, eat it, and it tastes like an orange, I can conclude it's an orange without eating an apple! The 229 has good torque. It's not because of it's displacement. Then what other reasons besides it's large stroke made the torque?

 

The engine components, heads, cam, intake are optimized for a 4000 rpm or lower redline. It can't make hp.

 

I got the point of the article, if you build 2 identical engines with different rotating assemblies power will be almost equal. I guess next time I am ordering a converter or camshaft I don't need to tell the guy anything about my setup other than the CI, cylinder heads and induction. If he balks I can just ask him if he read the hot rod article? Hey I need THE cam for a 350, can't be any difference they should all make the same power.

I sure hope the nextel cup car owners don't read the article, the engine builders have been ripping them off for years.

 

Philosophically, you can only determine it's an orange because you're comparing it with other objects in past experience which you were told were oranges.

Practically, you could only determine that the torque of the engine is due to its long stroke only by comparing it with an otherwise identical engine of shorter stroke.

 

Read the article thats covered in there. In Nascar and racing they are looking for every single and last hp they can get. Also those engine have to spin at very high rpms for extended durations on an engine designed to only last 501 miles. The difference we are talking here is 1-5 hp or really nothing.

 

Ok, I see where your coming from now. Unfortunately, there isn't another straight six I know of with that displacement but shorter stroke. I can think of a V6 but then that would be comparing apples to oranges.

 

In 1996 Hot Rod Magazine came out with an article called "The Smallblock Chevy Should Have Built". In a nutshell, a 327 crank, long rods in a 400 block. It can be read on the AFR website in their archive article section. It was my introduction to the long rod/short rod debate. I built one last year and planned to run side by side chassis dyno tests against a similiarly built but standard stroke 350. Unfortunately, I only got 50 miles out of the thing before my 8 hole developed a crack. It's getting repaired now but the more I study this creation, the more I realize how darn ignorant I am about the way things work. Here are some observations in no particular order. Although I haven't got them on the dyno yet, the long rod short stroke feels stronger. Not by a whole bunch but definetly stronger. Now realize that the car maybe optimized for greater success observed in the long rod/short stroke motor. This would be purely by accident as this is the way I bought the car. The car is a 1985 IROC with a 4:10 posi, full Spohn traction control, and a T5. With say a 3:50 gear, the advantage could have fallen towards the standard 350 if the standard 350 developed more low end torque. I don't know. The standard 350 has trouble staying out of detonation with the 11:1 compression (57 cc heads, .010 deck, .028" gasket, two eyebrow piston). Forget trying to optimize the timing even with premium. The long rod/short stroke will run on plus with no signs of detonation. Might even do fine on regular. Didn't get a chance to use it. It definetly leaves me with the option of playing with the timing without fear and the opportunity for more power because of that. So now were getting into the apples and oranges comparisons. Sure I could use race gas or octane booster on the standard 350 but now the comparison has changed. The perceived extra power from the long rod/short stroke could be attributed to many things not related to rod to stroke ratio with respects to crank timing and the whole piston dwell issue. The short piston skirt/ rod angle with it's inherent lack of friction (comparatively speaking) would be my guess to why a long rod/short stroke motor would make more power. Add that to the detonation resistance plus better breathing due to the larger bore and IMHO that's where the power increase comes from. Again, that's just my opinion. I will still run and post dyno runs but I'm confident the result will just bring many more questions. Maybe you all can help wrestle with those questions.

 

you guys talk about how the short stroke vs long stroke has nothing to do with power production and it is all in the induction


but stroke as well as rod size can all play a part in the induction of a motor as well.
longer stroke motors have higher pistons speeds vs shorter stroke motors

and with a much less extent how long the rod is plays an effect on pistons speeds

 

Yes it plays a part.

Is it a BIG part?

No.

Does it matter if you've already perfected and maximized EVERY OTHER DETAIL about your RACING motor?

Maybe.

Does it make a seat-of-the-pants difference on the street?

No.

Which is the whole point of the article.

The valve shrouding thing in a SBC, based on the valve spacing of the guides in a SBC head and the head bolt/push rod placement, loses its significance at about 4" bore. That is, going from a 3.736" bore to a 4" bore is a HUGE difference, because the bore moves from about 1/8" (.125") from the intake valve, to 3/8" (.375") or thereabouts; going from a 4" bore to a 4.125" bore is a MUCH MUCH smaller change, since the bore only moves out 1/16" (.0625") more, or from about 3/8" (.375") to 7/16" (.4375"). The exact numbers are different in a BBC but the principle is the same.