I don't know how you got the 8.3 CR number...but even at 8.3 with those gears and converter, 8.3 is dismal for anything. What pistons are used? Stock is typically 6.7 cc reliefs...and if so...again, my plug in numbers show you are only at 7.6 CR.
72 CC heads will bring you up to 9.12 safe for pump gas...and with proper carb and tune, you would be safe with 66 CC heads which would be 9.7 to 1 and require 91 to 93 octane.
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1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
