[rad400]

I am not an expert but as other have stated you can make plenty of power with a 4.25" stroker kit. I would save the 4.75 crank for the aftermarket blocks. I would hate to see a broken block over this. Good luck to you.

[ho428]

My question about these huge stroker cranks is at what length is the return deminished performance wise?
Other than valve shrouding using larger valves the whole down side of the 326 and 350 was the B/S ratio, with the bore being so small vs stroke, but it was still around 1:1. Using 2.5 and 2.75 strokes in a 4.25 bore or less block the B/S ratio is considerably worse than the 350, much less the 326.
You're also doing the same thing percentage wise of valve size vs the B/S ratio in a 4.25 or smaller bore and a 4.5 or larger stroke.

Are we breaking a threshold of piston speed with the longer stroke that overcomes this?

Inquiring minds just want to know since I've never built such a large engine or understood the theory on these long stroke undersquare engines.

[Steve Barcak]

Originally Posted by ho428

My question about these huge stroker cranks is at what length is the return deminished performance wise?
Other than valve shrouding using larger valves the whole down side of the 326 and 350 was the B/S ratio, with the bore being so small vs stroke, but it was still around 1:1. Using 2.5 and 2.75 strokes in a 4.25 bore or less block the B/S ratio is considerably worse than the 350, much less the 326.
You're also doing the same thing percentage wise of valve size vs the B/S ratio in a 4.25 or smaller bore and a 4.5 or larger stroke.

Are we breaking a threshold of piston speed with the longer stroke that overcomes this?

Inquiring minds just want to know since I've never built such a large engine or understood the theory on these long stroke undersquare engines.

I am not sure there is a limit. Everytime Pontiac increase the stroke, it made more torque and, generally, there is no replacement for displacement ( other than supercharging or N2O ). You just move the power curve down the rpm scale depending on many other factors- rod length ( limited by deck height ), head and induction capacity, etc.
It is the same way with other engines too. or they would not make giant engines with monster strokes.

[estep455]

i have a friend that runs a 4.75 stroke crank and is .100 over on a 400 block. he runs it in his dragster and i wont get in the other lane against him! shifts it at 6k and runs 5.0s (1/8th mile) been 4.90s. cant get him to buy an aftermarket block and he has a gift certificate for a grand off! i still say my 535 with standard port heads will whip his and he has wide ports on it.