My 427 is a true 11:1 engine and I'm running 91 alcohol free fuel in it with the timing turned down to 35 degrees. When I go to the track I use 110 with the timing at 39 degrees. No problems so far. I have open chamber aluminum heads which may make a difference.
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Freddie
1969 Camaro RS/SS396 (427) 4 speed
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