It depends also what altitude the car is being ran at
I am at 4500 ft and I have a 440 with 12.5:1 compression and aluminum heads and run pump gas and have no problems
I was going to mention that and glad someone did.
At 5,500 here with 9:1 Iron heads and can run 87 just fine, but sometimes I go to Phoenix which is a few thousand feet lower and I have to pull a couple of degrees or run 91.
