The old TRW pistons we dished had top thickness of over 3/8" of an inch and it was no big deal to take a .200" cut out of them. Most new flat top pistons are pretty thin on top.
I come up with 11.7:1 using the Wallace calculator and a standard .039" thickness FelPro head gasket.
The following is only for speculation and I sure don't want to be responsible for results if it is tried.
Staying under .050" piston to deck clearance is only the first part of the no-man's land. Usually a FelPro head gasket is .039" so the danger area is anything over .011" piston to head since the total of the two would be right at the .050" limit of the danger zone for detonation. The actual high detonation area is usually stated to be between .050" and .080" where chance of detonation is highest. I have read that the flame front doesn't like that defined area and once the clearance is greater than .080" the risk of detonation falls to normal levels. So zero deck and a .090" Cometic MLS gasket might work. Would be really interesting to have someone take the risk and report back. I show 10.42:1 with the thick gasket.
Also, I've had terrible luck with copper head gaskets without the fire ring insets. Normal machining seems to always have a dip or rise with a failure to fully seal and the copper just doesn't conform to any imperfection.
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Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress.
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