rinderr

What is the best fuel octane / mix for a 66 Mustang with a 289 HiPerformance engine.

I was told to use Sunoco 94 octane + octane boost + no lead substitute.

Any other recommendations?

KeMo

I would think it all depends on the compression ratio. I would also think that the shop that did the engine work or sold you the parts would be of some help. You mite try some aviation fuel mixed 50/50 with pump gas. Avgas is over 100 octaine. I dont think you need leaded gas cause your valves more than likly have been upgraded.

Ohio XB

Octane requirement is solely based on compression ratio. What is your CR? Octane level required is to prevent knocking.

Also, if the heads have been reworked it is possible they have hardened exhaust seats already and you don't have to worry about burning up a valve. If you have aftermarket heads, not sure how it is in Oz, but in the states there is no worry at all.

Don't waste your money on octane boosters. They can only raise octane by less than 1 whole number. When they advertise "...will boost octane by 3 points..." they mean by .3 , not going from 94 octane to 97 octane, but from 94 octane to 94.3 octane. Just buy gas in the octane you need for your compression.

Steve