On Tue, 23 Jun 2009 16:46:46 -0700, Grant Erwin
wrote:

One of my compressors has bore 4" stroke 3-1/2" two cylinders (single stage)
and can run at 900 rpm max.

I am trying to figure the displacement CFM and I'm coming up with an astonishing
and quite unrealistic 45.8 CFM.

I think the actual number is more like 14 to 18. But I can't see what I'm doing
wrong.

Help!

3.14 * 2^2 * 3.5 * 2 / 12^3 * 900 = 45.82-ish

Displacement is displacement, delivery at 0 psig pressure if the
valves can work with near 0 psig pressure differential. Your
numbers look correct.