They are NOT designed for ANY spirited driving especially being they are cast. As far as I know there have NOT been any design changes forever. Compression will be way lower than stock. They were supposed to be 10.25 from the factory but in reality the BEST I have EVER measured was 9.75-1 & this was with the ORIGINAL piston in the hole at .040". On average they are in the hole .055" which lowers it even more. Then use the composite head gaskets on a 425 & you loose another .44-1. On a 401 it works out to be .77-1.
Tom T.
Tom Telesco
Classic and Muscle Automotive
12 Cook St.
Norwalk, CT 06853-1601
Day Phone 203-324-6045 ET
NailHead Mini-Starters '53-'66
Adjustable Roller Tip Rocker Arms - All NailHeads
Custom forged pistons
Front & rear neoprene seals
Many other "Nail" parts
"If I can't get it, you don't need it!"
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