not really EFI-related, regarding compression ratio reduction.

[Jon]

Compression ratio is (BDC volume)/(TDC volume). TDC volume is sum of
head chamber volume + volume due to head gasket thickness + volume of
piston dish.  BDC volume is TDC volume + displacement per cylinder, eg,
43.75 cubic inches for a Chev 350.  Measure head chamber volume by
turning head upsidedown, placing a clear piece of plastic over the
chamber (the plastic has a small hole) and then pour water into the hole
from a graduated cylinder. The plastic allows you to avoid the miniscus.
Seal the plastic with grease. From this it is clear that piston
geometry, stroke, head gasket, etc all will alter CR.  TVR Jon

Ed wrote:
> 
> For X amt. of CC's increased in a combustion chamber, how many points of
> compression does this reduce? Or will such a formula not work?
> 
> -Ed