Thread: Exhaust size and velocity

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Originally Posted by SBC

65cayne's post got me thinking - watch out!

What is the rule of thumb for header/exhaust diameter?

Too small - air throughput is restricted.
Too big - velocity is reduced.

I would think the ideal diameter is a function of actual CFM througput.
Or perhaps the target is an ideal velocity that is a function of CFM and diameter.

First you need to know what your Intake to exhaust ratio is.
Go rent a chassis dyno with you buddies and try different tube dia's,collecter length,step headers etc.