What octane to run on 4.6 GT Anyway?

Mustang5L5 said:

If you are installing a 93 octane race tune, then the factory ECU map for 87 octane goes out the window. You are no longer stock.

Three major reasons to increase from 87 to 93 octane typically are forced induction (super charger, turbo, Nitrous), increase in compression, and a change in engine tune altering fuel/timing curves. You are doing the latter. More aggressive timing curves will require higher octane to prevent detonation.

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Mustang5L5 said:

Not always the case. The new 5.0 Coyote Mustang has 11:1 compression and it can run on 87 octane. It does so by changing the timing curves. It won't make as much power, but it will prevent detonation. But if you put 93 octane in, it will run more aggressive tune and make more power. This is how the ECU was tuned. and it has various sensors to help adjust.

So compression is not the only criteria when determining octane level. It also depends on engine tune..which you are changing by installing a performance tune. You'll need to run 93+

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