Mathmatical formula for...

[Sparkroost]

compression.

Would anyone know a basic formula for expected compression with the variables of Bore, stroke, cylinder head volume, port height(or total distance of compression)?

[Terry Jackson]

In theory it's total swept volume divided by total volume @ Top Dead Center. In reality, at cranking speed, it's total volume when ports are closed divided by TDC volume. It can change with rpm at port velocity & exhaust pulses can add aor subtract volume just before close, meaning dynamic CR doesn't equal static CR.
Run a compression check & divide by 14.7 & that is your static CR for those conditions. 14.7 lbs=1 atmophere. Compression of 147 lbs = 10 to 1 compression static compression ratio. Running CR on a well built/ported engine would increase those numbers. CRxVE(volumetric efficiency)= actual CR.
Some of these race guys can probably explain it better.

[Sparkroost]

Thank you. It's a little more difficult than I initailly thought. Air flows better, more fuel/air enters the cylinder. and POW.. more power.

How can I compute how much material needs to be removed in order to gain 10lbs static compression and... Is this what I should do, or should the heads be cc'd due to not knowing the dynamic compression? How can the dynamic CR be measured?(with the engine running at different rpm's? Dyno?)

I have a few facts to note.
Port
150 psi stock head gasket
140 psi low comp gasket

This particular head has been "cleaned up" who knows how many times.
Have a new head... 130 psi, thick head gasket. I was thinking of putting a std. head gasket on the low psi head and see what happens.

Maybe I am missing something. Say the original head was cut .010 total.. Would this account for 10lbs static compression on a crossflow?