Rick, as per Vader's response, combustion chamber design is the one thing that you can't measure to help you out.
The distance that the flame has to go to get to the other side of the cahmber, and the amount of swirl (i.e. air movement in the chamber) just prior to ignition makes a huge difference.
A 4.5" bore with an open chamber, and a plug mounted at the side will detonate long before an advanced "clover" shaped chamber with a central plug, on a 3" bore.