Model A compression

[ms fowler]

Every math teacher who ever heard " Will I ever really use algebra??/" is smiling at this thread.

 

[nkaminar]

Dodge has hit the nail on the head. There are a lot of factors that enter into what compression you measure and what it is when the engine is running. Air has momentum so the cam grind is meant for an engine running at it's normal rpm. Plus there are losses as the air flows through the carburetor, through the manifold, and through the intake valve. The math is only math, not reality.