What octane to run on 4.6 GT Anyway?

[Bruno Rodrigues]

Like I’ll have to put 94 octane in it if I apply the race tune, it’s just the 9:1 compression stays the same regardless of tune and usually higher octane fuels are only used on higher compression vehicles such as the Mach 1 which have a 10.5:1 compression I think

 

[Mustang5L5]

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.

 

[Mustang5L5]

usually higher octane fuels are only used on higher compression vehicles such as the Mach 1 which have a 10.5:1 compression I think

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+

 

[Bruno Rodrigues]

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.

Ok sweet sounds good, thx man. If I do change back to 87 from 93 for daily driving, fill it up with 87 first, use it up, fill up again and change the tune? Cause I only really use the race tune when I go to the track and gas is pretty expensive as it is lol

 

[Bruno Rodrigues]

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+

Ok that’s cool thx man

 

[Mustang5L5]

Ok sweet sounds good, thx man. If I do change back to 87 from 93 for daily driving, fill it up with 87 first, use it up, fill up again and change the tune? Cause I only really use the race tune when I go to the track and gas is pretty expensive as it is lol

If you go back to 87 octane, you can just immediately switch. The danger is less with the higher octane 93 gas in the tank running an 87 octane tune.

It's just when you want to go to the 93 octane tune you really want to make sure you run that tank down as low as possible before topping it off with 93 octane to make sure you got it all out or really dilute what little 87 octane is left into the rest of your tank of gas.