The 427 Camaro has always (since 84) run on straight AV fuel with a lead additive. At 12.5 to 1 with open chamber heads, it runs great with temps in the 170-195 range. It does "barf" throught to overflow though in the heat of summer(???) The 427 Impala has just been put on a 50/50 diet the same way. At 10 to 1 with oval heads, I don't think I'll have any problems. Have a Good Thanksgiving!
Jeff
x2