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Thanks John for the cc info. and all your guidance.

So if I use the feeler gauge numbers it looks achievable...
.073 chamber depth
less .039 dome height
less .010 off the heads
add .020 head gasket
.043 total quench

With .010 off the heads, that will reduce CC's to approx 80-81. The piston is .034 in the hole which equates to approx 6.8 cc. Valve reliefs are at 1.8 cc based on KB236 spec. So with a total CC at approx 88.6, what would the SCR be...around 10.0:1?

I'll take your suggestion and polish the chambers the best I can shy of removing valves to accomplish any major ginding.

Not sure if it's worth anything, but while the heads were off, I selected 8 spark plugs that were indexed correctly.



I think if you can get .043 quench you will have a good chance. The pfirst build I helped out on had roughly the same quench, same pistons and 73/75 cc 906 heads, the guy had no issue running on the street with 93 oct, but this was back before Ethanol, but I think the gas had MBTE in it ??

The odd part was that this build mimic'd his friends build, I was just involved with collecting parts and doing chamber mods on the heads, and his friends engine with 9.5 compression and .065 quench woulkd not run on anything less than 93 without pinging, they both ignore KB's recommendation of 34 max advance ?

If it were me I would take the .010 out of the open part of the chamber that way you end up with perfectly matched chamber depths and add CC to the chambers.

What part of Ma. are you in ?