Hi Andy,
Im running a 302 block bored +030" to suit all my 351C innards,with Aussie Quench Heads. Have ported/polished the heads and matched all of the chambers cc (using a pipette and parafin)and hardened exhaust seats, which will gives me 10.2:1.
Any more than that, unleaded will give detonation problems and all sorts of additives would be needed to protect the heads in general.
Before my head gasket went on the way back from the SVA, compression was up at around 11.4:1 (way too much for the road) IMHO{-}
Regards
David
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