It depends upon if you have a TRUE 10:1 compression. Be sure to take into account...how far the pistons are down in the bore at TDC
cc's of the valve reliefs
cc's of the head gasket
truee cc of the combustion chamber
A set of '10 to 1' pistons does not necessarily give 10 to 1 compression.
One more thing, running on the 'low' side of the compression scale for a given cam, the low-end and midrange are what will suffer the most. This is especially important when using a cam that is a bit on the large side anyway... especially if it is to be used with an automatic.
Good Luck!
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Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220