[Firebob]

All other things being equal( as much as possible), I was wondering. Seen lots of sheets for 455 dyno pulls but I don't think I've ever seen any dyno numbers for a stroker.

[gtofreek]

A 400 stroker and a 455 are pretty much the same thing. The common 400 stroker engine[460-461] is only .040" more stroke, which amounts to very little. The main advantage with the 400 stroker, is the smaller mains. The blocks are stronger because of this, and they can handle RPM's better with less surface area to keep oiled.

I posted dyno pulls for a 455 and a 460 stroker on here, but the stroker isn't really a good comparison because of the 64 389 heads that were used. They really choked it off. It made 386 HP and 516 ft. lbs. It did however, make over 500 ft. lbs. from 2800-3800 rpm. I have also posted dyno video and sheets for a 500+ HP 400 we did.

[Will]

Yep. Cubic inches are cubic inches whether it's a bored and stroked 400 or a bored over 455 doesn't really matter that much to power production as long as the resulting displacement is close to the same. The only real difference is the main journal diameter and that has almost no effect on power output.

[Firebob]

So there isn't that much difference between getting you're cubes from a longer stroke/smaller bore(400) vs shorter stroke/bigger bore(455).
Added cubes from stroke = same as added cubes from bore, as far as Hp and TQ are concerned?

[54nomore]

Yep. Cubes are cubes, pretty much. And besides, the 455's bore is only .030" bigger than the 400's.

[gtofreek]

400 = 4.120" x 3.750"

428 = 4.120" x 4.000".

455 = 4.150" x 4.210

460 stroker = 4.150" x 4.250

461 stroker = 4.155" x 4.250"

[1969GTO]

is there a weight difference?

[gtofreek]

Very little. From what I have read, all Pontiac engines from 326-455 weigh within about 10 lbs. of each other. I haven't actually weighed one myself.

The 400 blocks are a little stronger with 1/8" more meat in the block, around the mains, and the main cap thickness.

[Will]

the small journal cranks are definitely lighter. Not sure by how much, but there is a difference. Maybe 5-10 lbs max.

And yeah, the bore size difference is negligible. If there was a big difference in bore size then that could definitely affect power production due to breathing differences.

[Firebob]

Ok, that makes my decision somewhat easier. If there was a significant performance advantage to the stroker then that would be the way to go but seeing as how I have nearly all I need to build a .030 over 455 and still be able to keep my 400 in tact, that seems to be the best way to go. Never hurts to have a great running spare motor in the corner.

[AdamIsAdam]

Originally Posted by gtofreek

400 = 4.120" x 3.750"

428 = 4.120" x 4.000".

455 = 4.150" x 4.210

460 stroker = 4.150" x 4.250

461 stroker = 4.155" x 4.250"

And...

469 = 4.190" x 4.250"

http://www.csgnetwork.com/cubicinchcalc.html

[Donovan]

This seems to be another Pontiac secret in plain sight. But guys are still gonna give a lot more money for a stock 455 shortblock than a good 400 to build. people are strange.

[Formulajones]

Originally Posted by Donovan

This seems to be another Pontiac secret in plain sight. But guys are still gonna give a lot more money for a stock 455 shortblock than a good 400 to build. people are strange.

Yep, I pointed that out before when the OP started another thread about it. With good 455 cores drying up and commanding higher prices, it just makes the 400 stroker option a better deal all around in my opinion.

[HWYSTR455]

Isn't TQ technically directly related to stroke? The more stroke, the more theoretical TQ? And theoretically, max TQ is theoretical max stroke at 5250 RPM? More stroke, more mechanical leverage, IE, more TQ?

If you could have a 5" bore, and only have 3" stroke, you would only make around 300 ft lbs, theoretically. Correct?

Believe there's a point of diminishing returns too, like over X stroke, compared to bore, so bore/stroke ratio is an important factor as well.

.

[GOAT WHORE]

Longer stroke will produce more torque but in the case in question by the op there would be very little noticeable difference between the 4.210 and 4.250 strokes, at least that's how I understand it.
Max torque is not at 5252. 5252 is where torque and horsepower meet or intersect on a dyno. It all has to do with math or something

[HWYSTR455]

Ah, math, guess that's why I got it wrong!

[PunchT37]

Only good thing about the 455 is most blocks can go 060 over without problems. So, one can add 060 to a 4,151 bore instead of a 4.12 bore so, the 455 "soaks up" a 30 over 400 block.

Add to that, one doesn`t have to get an aftermarket crank to make 500 plus hp. The stock 3.25 main cast crank will do that all day.

So, the 455 isn`t totally useless.

[1968firebird455]

I have one of each, just havn't gotten the 455 in a car yet. The 461 is a fun motor if you have the traction to put the power down.

[tpssonic]

"Isn't TQ technically directly related to stroke?" Yes, in that a longer stroke (all other things being equal) will make peak torque at a lower rpm. Longer strokes equate to a higher piston speeds at the same rpm.

[Will]

Realistically, torque is more closely linked to displacement. A longer stroke (all else being equal) means more displacement, thus more torque.

Build a 350 and a 455 with all the exact same parts other than crank & pistons and the 455 makes it's peak torque at a lower RPM because of the breathing characteristics of the engine, not because the stroke is longer. The cam and heads will produce peak volumetric efficiency at a certain volume of airflow and the larger engine reaches that volume at a lower RPM because each cylinder can pump more air with each stroke. Put a bigger cam in the 455 and it can achieve peak torque at the same RPM as the 350.

While true that a longer stroke gives a longer lever for more mechanical advantage, there are other factors that come into play that make longer strokes problematic - like increased piston speeds and the resulting inertial loads as well as breathing issues if the bore size isn't big enough to allow the use of adequate sized valves with minimal shrouding.

5250 RPM is the RPM at which torque and horsepower are equal. This is true for any engine and is a result of the mathematical formula used to calculate horsepower from torque and RPM.

Peak torque could occur well below that or well above that depending on many other parameters. A 14,000 RPM motorcycle engine makes peak torque well above that number whereas a big diesel that never gets above 2500 RPM makes it well below.

People put longer stroke cranks in engines because it's the only practical way to achieve a large increase in displacement with a given block. It's the increase in displacement that results in the increased torque more than anything else. The longer stroke does contribute something, but it's a small contribution in comparison to the simple displacement increase.

A Chevy 454 and a Pontiac 455 that are built with heads that flow the same and the same cam would produce right about the same power numbers even though the Chevy only has a 4" stroke compared to the Pontiac's 4.210" stroke. The Chevy can more easily be built for higher RPMs though due to it's shorter stroke and considerably larger bore.