I have a 1966 mustang 289 4bbl holley carb. I'm using the 89 gas which is one step above 87 but should I be using 91? What are the pros/cons? Any suggestions will be greatly appreciated. Thanks in advance.
the only reason you would want to use a higher octane fuel is if your are having a problem with detonation. if this is not a problem for you use what you have been useing, or go down a grade and see if you get a knock under a load and if you still don't, you sould be able to use that without any problems.
Even back in the day we had pre detonation. Some cars were worse than others. We also called it "spike" and "ping". Whether or not you need higher octane depends on how your engine runs. It would be hard to completely stop ping without a modern computerized ignition control considering it is in many cases "the nature of the beast"
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