can anyone explain the difference between small block torque verses big block torque...

people always say that big block torque and small block torque are NOT the same

and if you think about it torque IS torque....torque is torque..it takes torque to say bend a metal flyswatter handle

but why is it that you could take lets say a 4000 stall converter on small block that stall 4000 and a big block it would be good to get 3000

anyone have a logical explanation for this?

 

In so far as the seemingly nonsensical statement that "big block torque and small block torque are NOT the same" goes, I guess that it refers to the differences in torque curve between a typical BB and SB setup that make the same peak torque. In that circumstance, say a 454BB vs. a stroker SB, the 454 would be in a milder tune and, of course, a lot bigger displacement. So if the peak torque were about the same, the BB would have a much wider torque band that was lower in the rpm range.

I guess the differences in the way it would drive would be obvious. The BB would have much more torque down low and probably "feel" a lot faster, though it would run out of breath a lot sooner and not rev as high. On a track, there might not be much of a difference in all out performance, depending on a number of other variables. Transmission and gearing would play a big role here. If the SB were setup to be able to stay in it's narrower power band it would do so with higher gear ratios and might actually be faster than the BB, even with less "area under the curve" as far as the powerband goes.

That's the best I can do at 6am.

Rich Krause

 

Well put at any time.

Of course, Ford torque is a LOT different from SBC torque!

 

Yeah, because there's less of it with the Fords.

 

Great minds think alike!

 

Yep there's no difference between any type of torque. If you can hold it higher than you make more power too but 500 ft lbs from either is the same as far as the tires care. Big Blocks usually have more tq since they are bigger though. Tq is mostly engine displacement dependent. Of course blowers or turbos or NOS can change that!

 

There is one difference between BB and SB torque. Past about 500ft-lbs sb torque is alot more expensive.

BBB

 

Don't forget stroke... leverage on the crankshaft is an absolutely integral part of torque production.

A 4.25" piston coupled with a (formerly) 350 CID engine's 3.48" stroke wouldn't make a radical difference in the torque production or characteristics of the engine, even though displacement was increased to 395 CID. However, if you couple that 4.25" piston with a 4.0" stroke to increase leverage on the crankshaft, that's one reason why a 454 will make more torque over the usable rpm range (especially at low rpm) than the average small block, even if their peak numbers are identical.

Today, you can relatively easily (if not cheaply) achieve "big block" (427-454 CID) displacement in a small block package, but you still have the size limitations of the package where the top end is concerned. Even the best small block head is no match for many of the performance big block heads available. You simply cannot package the port length, height, or volume of a big block head in a small block package, and that's why the big block will always have a power potential advantage over the small block, even with identical displacements.

 

 

Tq is strictly a function of VE and Displacement. How far you can keep making this TQ go in terms of RPM is in the heads you can run. Anyone knows Big Block heads are better than small block heads, there's no new ground there.

However there are heads that can easily fill any size small block even 450 inch ones. You just have to know what you are doing. 14 degree Pro Actions or any of the decent canted valves can fill these engine just fine to name a few. Now the 23 degree SBC heads do start feeling the heat but that's no reason to build small.

We've done larger small blocks with over 750hp at the school and they do weigh a LOT less than any big block. That's also with only 23 degree heads!

 

I wasn't comparing a short stroke 395 to a long stroke 395, I was comparing a short stroke 395 to a short stroke 350.

If you're saying that you can just lump an increase in stroke into the "more displacement" argument, then I'd agree, but you'll get a greater increase in displacement from stroke than you will from increasing the bore, so stroking can't be ignored either way.

 

 

Maybe you should look at some more realistic examples...

Bore increase
4.00 x 3.480 = 350 CID
4.03 x 3.480 = 355 CID (+1.4%)
4.06 x 3.480 = 360 CID (+2.9%)
4.09 x 3.480 = 366 CID (+4.6%)

Stroke increase
4.00 x 3.480 = 350 CID
4.00 x 3.750 = 377 CID (+7.7%)
4.00 x 3.875 = 390 CID (+11.4%)
4.00 x 4.000 = 402 CID (+14.9%)

It's the rare small block that will allow a 4.25" slug, however, you can fit a 4.000" crankshaft into many of them with a little work. Realistically, you're going to get a greater increase in displacement from increasing stroke in almost any real world application because of the limitations on bore diameter. On paper, however, you're right. Bore increases displacement more rapidly than stroke.

 

Jim, stroke has little to do with torque production (it does have an impact but I’d bet that in 90% of real world examples it adds up to less then the error that you’ll see on a dyno trying to chase it down). As has already been said here, torque depends on displacement and VE, nothing more and nothing less. The only reason that long stroke engines tend to appear torque biased is that it’s harder to build them to rev so people tend to build them in a way that matches the rpm band that the parts they have available to them will survive. What you end up with is an engine that produces the same peak torque (assuming similar VE’s at the torque peak) but at a lower rpm, and because of the lower rpm for the power band HP is proportionately lower…