I'm trying to calculate the exact compression ratio for my blown stroker motor and found this calculator on-line; http://www.csgnetwork.com/compcalc.html
I have all the information needed to plug in the numbers, except for "Head Gasket Bore Diameter"  I am not exactly sure what they mean and I don't have a set of Fel Pro gaskets to measure this dimension. Can anyone give me a number to plug in here? That is not a perfectly round area anyway so I am not exactly sure what they are looking for.

Also, there is no provision in this calculator for a relieved block. Is there a % reduction ( i.e. 1% or 5%) that can be subtracted from the calculated CR? 

Thanks,
Rono

  Ron Lane,  Meridian, ID