Linster

Stoke makes more low end torque than bore. Both make torque, but stroke adds low end torque, bore is better for high rev's HP which boats do not normally do

Linster

How much bigger valve can you get on a BBC other than 2.25 Intake and 1.9 Exhaust? 4.6 bore is tops, Maybe a little but you have to have custom heads to do better.

bcarpman

Looks like I'm a glutten for punishment again. Seems everytime someone posts an engine myth, and I explain what's going on, I get beat up about it, but here goes:

The myth that stroke produces torque and bore produces HP comes from the fact that "all else being equal" when you increase the stroke, you aren't able to put bigger valves in, and hence airflow doesn't increase, hence torque goes up, but HP doesn't as much, since HP is a function of total airflow through the engine.

But, generally, if you increase the bore, you'll also put bigger valves in the head, or at the very least, unshroud the existing valves. This allows HP to increase, usually at the expense of bottom end torque, since the builder will then cam the engine for the top end HP.

Also, on high strung race engines, the RPM limit of the engine is based on piston speed, which increases with stroke. So that's why you'll see large bore, small stroke on displacement limited racing classes. Which of course also end up being very low on bottom end grunt.

Really has nothing to do with the stroke per se, and more to do with how the engine is setup.

Personally I'd NEVER turn down extra displacement. If I were worried about low end torque breaking drives, I'd simply give it more cam. Then I'd end up with the same low end torque and more top end HP due to both the displacement increase and the bigger bump stick.

ghittner

Strokes don't break drives, people break drives period.

Donzi502

Guys my take on this is that the bigger the arm the more control you have over it with the piston and rod. I would like to see anyone make serous torque with a 3" stroke. Wouldnt matter how much bore you have. By the way i love it when people tell me what i cant do. I gurantee i will make 800 or very close to it with 532. We have some not bad 98 octane pump gas down here. The queation is weather to use a 4,1/4 crank and make some more. The only limitation to the power is weather my wallet will streach for the heads and sheet metal intake required to make that power.
Check out this site for some big power options. These boys do marine engines and also confirm they can meet our HP need from a 532 marine engine or can supply heads and intake to do the job
www.sonnysracing.com/engines.php

bcarpman

If you already know the answers, why did you ask the question?

If you could get the bore to make the same displacement with a 3in stroke, and you camed it right, you could make the same torque. It really doesn't matter what "your take on it" is, it's just basic IC engine theory.

Stroke may give you extra torque ON THE CRANK for a given force on the piston, but a bigger bore will give you more force on the piston top and hence the same overall torque out of the engine. Again, this is only if you don't go for more top end power with bigger valves, etc.

KAAMA

iTrader: (1)

Interesting thread-----I will probably never do this, but I've always been interested in a 4.600" bore x 3.76" stroke (427 crank) naturally aspirated engine which brings it to somewhere right around 500cid. Just seems like it would be a fun project with that bore x stroke combo (not sure how long of a rod it would need) and some killer heads like the 315 AFR cnc'd heads I have now and see what kind of HP/Torque it would make @5800rpm.

Right now I have a pair of NA short deck 565cid engines 4.25" stroke x 4.600" bore (6.385" rod) with cnc'd 315 AFR's, Dart intake w/single Holley 950cfm, 9.5 cr, and Stellings full length tubular headers. It would be fun just to compare notes between the two different cubes size's.

NOMOGOFAST

I agree w/ ghittner, people break drives. I would like to see a 532 cid motor w/ no blower make 800hp. This can be achieved, but at what compression.... 14 to 1. Let's see how long a 14 to 1 motor lasts in a marine race application. Sonny is the man for power, but a, na 532, 800hp

articfriends

iTrader: (1)

Mark,if you did that bore and stroke it would be even more interesting with a solid roller at about 6800,Smitty

PatriYacht

800 hp can be done from 532 ci no problem. But how much will it cost? Custom ported heads with valvetrain to spin 7000 rpm, sheet metal tunnel rams, dual Dominators. Right there you've got 12-15,000.00. And think of the maintanence. I'd build a tall deck 4.6 bore x 4.5 stroke with Afr 357 cnc heads, Super Victor intake and a moderate solid roller to get 800 hp and put to rest of my money into a better drive. If you're going racing even a high rpm, low torque engine is going to break drives.