turbo SBC's... was RE: Thanks for the EFI! (off topic)

Greg Hermann bearbvd at mindspring.com
Tue Dec 11 05:47:34 GMT 2001


8.5:1 compression

Might go a bit higher than this with WI.

>and cam specs based partially on the current engines backpressure vs boost
>characteristics (measured when I strap this tired mule to the dyno - will be
>fairly mild with duration),

Short duration, high lift, wide lobe centers (mebbe 116).

Take a peek at rollers, or even BETTER, mushroom tappets.

and some custom JE/Venolia/KB pistons.

JE and Venolia use pretty much 2018 alloy forgings (high expansion). KB's
are generally cast hyper(ujunkit).

TRW uses something that is a proprietary version of 4032 alloy forgings.
(Lower expansion) This is a better approach for most anything but a fueler.
There are others besides TRW who will do 4032 alloy.
>
>My reasoning is to make a reliable, build it once road racing/street fun
>engine. I still am considering a 377, but I like the detonation resistance a
>smaller bore gives you.

The side thrust on the bores with a 377 is a pretty serious matter with boost.

 The question of the hour is whether I'll make more
>power unshrouding the valves with the larger bore and less boost. I'm
>planning on going to about .035 quench,

Go for it !!!

but some folks more experienced than
>I claim that a quench that tight really disturbs the flame front travel at
>TDC.

The trick here can be some little channels to sort of "direct" the
turbulence as the gas comes out of the squish area--this keeps the
turbulence pattern in the chamber more consistent, and avoids the
"roughness" these guys are likely talking about.
My pet theory is that the "roughness" comes from inconsistent patterns of
turbulence in the chambers causing  variation in the burn time--sort of as
though you were jiggliing the timing.

To knock down compression, I plan on mirroring the combustion chamber
>shape in the piston, since this should give you the fastest burn time.

This sounds good IF you really need to do it. How high would the squeeze be
with flat pistons??

 Some
>words of wisdom from the previously mentioned turbo folks suggest going with
>a plain 'ole open bowl piston,

NAH.

>Any thoughts or comments before I'm committed to building it? Thanks!

There you go.

Greg
>
>------------------
>Andris Skulte


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