what is the mathematical equation for:

[curtis]

What is the mathematical equation for calculating the psi of compression in a cylinder when the piston reaches tdc.

here are the known facts:
bore 4.030 in.
stroke 3.75 in.
deck height .010 in
valve reliefs 2 @ 12 cc
heads 72 cc
head gasket 9.3 cc

the compression test is run with the rockers off and engine cranked by starter.
our biggest question is what happens to the psi if go to a 3.1 cc head gasket.with the figures above our test comes out 150 psi.

 

[bossvette]

the tech center button at the top of the page has a bunch of formulas for figgurin' out stuff.

 

[curtis]

Bossvette, can't find the formula I need in the tech stuff. any other suggestions.?
curtis

 

[bossvette]

Just a guess but try the formula for compression ratio and multiply by 14.7 psi which if I remember from my school days in the late sixties is the atmosperic pressure at sea level

Compression Ratio = (Cylinder Volume + Chamber Volume) / Chamber Volume

 

[drags1998]

I have never herd of a formular for this . DOSENT mean there isnt one, just never seen anybody want to know this!!!! NOW, compression ratio is a different story!!! everyone wants to know this!!!

 

[Hrtbeat1]

Mark's says

(Displacement + clearance volume) / clearance volume = Compression Ratio

All else being equal by reducing your head gasket thickness "clearance volume" you should increase Compression Ratio.

 

[curtis]

the reason we need this formula is because in our racing class they do this compression check. If under 175 psi then its legal. if we use a formula we will be able to figure out onpaper the results from milling heads, gasket thickness changes etc. so we don't overmill and ruin something or buy gaskets we can't use. again the test is with rockers off, some cam and duration don't affect the results.