Different Strokes

[John Andrianakis]

David Sagers wrote:
> 
> I'm building a twin turbo small block chevy for a 1981 Corvette, auto trans and all the power accessories.  It'll be used for a hotrod street car, primarily on weekends and sunny days.
> 
> In a conversation with the machine shop this afternoon the engine builder said I should consider going with a shorter stroke.  I can build a 4" stroke 434 ci, a 3.75" 406 ci, or a 3.48" stroke 355 ci engine.  The block I have is already clearanced for the 4" stroke so the additional cost of preparing the block isn't a factor.   I already own the 4" crank and rods, and the crank can be traded out for a shorter stroke without any additional cost.
> 
> The builder said that a short stroke engine will respond better to a turbo as it'll rev faster.  So I'm looking for someone with knowledge and experience with turbo engines.   Do I go with the shorter stoke that'll rev faster, or go with the 4" stroke that makes a lot of torque, especially in the low RPM ranges.  Low RPM torque seems to be important as this is going to be a street engine generally run in the lower RPM ranges.
> 
> Some of the things I want from the engine are throttle response and low rpm power.  I was hoping that by going with the big 434 ci engine I could over come some of the slow acceleration associated with turbo lag in small engines.

I think turbo engines like longer stroke better. Long fat exhaust pulses
help turbo efficiency and reduce spool up time. Reducing freewheeling of
the turbo assembly is a worthy design goal that can be achieved in two
ways: longer stroke and better exhaust manifold design- equal length
-180 degrees headers.
Just an opinion.
John Andrianakis.