CFM Questions

[Gary Derian]

Talk of CFM is very confusing.  When someone has a 600 CFM Holley, it means
if flows 600 CFM at 1.5 in. Hg pressure drop.  That same carb will flow 840
CFM at 3" and 350 CFM at 0.5".  There is no absolute flow limit until the
air reaches the speed of sound.

So how much can a TPI runner flow?  Those are known to be small and limit
power above 4000 rpm.  Sure you can boost the daylights out of it but that
creates excess heat and backpressure.  I think if you had 15 psi blowing
through a TPI runner to atmosphere you would have really high flow but that
is meaningless.  You need flow in pulses and you need to have very low
pressure drop.

Most guys that build engines don't really know what goes on.

Gary Derian <gderian at oh.verio.com>

> Anyone know how to calculate CFM rates?  I was talking to the shop that's
> building the turbo set up for my chevy engine.  He said that at 15 lbs of
> boost each runner on a stock TPI will flow 600 cfm.  I think the stock
> runners are 1.25"  But 600 cfm sounds really high for such a small tube,
> even at 15 lbs of boost.