91 octane tune compatable with 110 or 100 octane?

I just installed a TT kit and I am running a 91 octane tune since that is all I have here in CA and E85 is not near me. Can i mix 100 or 110 octane with the 91 octane and not have any issues? do i need a re tune or a separate tune when mixing the octanes? Or will I not have any issues when mixing these octanes. Thanks

Shouldn't have any issues assuming it isn't a heavily oxygenated fuel. Depending on how conservative the tune is, you may not gain anything, may even lose hp, from the higher octane.

You're going to want to stick to a fuel with a similar stoich to regular gasoline, so unleaded 100 would be fine. I wouldn't throw leaded 110 gas in there. Though I think it would be considerably easier to put Boostane or Torco in than go through the headache of mixing the right amount of 100 with 91.

Barrel said:

You're going to want to stick to a fuel with a similar stoich to regular gasoline, so unleaded 100 would be fine. I wouldn't throw leaded 110 gas in there. Though I think it would be considerably easier to put Boostane or Torco in than go through the headache of mixing the right amount of 100 with 91.

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How's boostane with long term usage? Am I going to mess things up?

so mixing 100 wouldn't do any damage and I wouldn't require a new tune or anything? Like barrel said, will the boostane or torco mess anything up or cause the engine to not respond well?

Trims will be off due to the difference in fuel's Stoich's values.

Long term usage of an octane booster could have an effect on cats, but so might long term usage of forced induction, so...

Stoich of something like Sunoco 260GT 100 octane is 14.1 where standard gas is 14.7. So too much 100 and you could be throwing your car's fuel trims off and maybe cause a lean condition.

Something like Boostane won't do that.

The only negative effect I have seen with octane boosters is a slight orange deposit on the exhaust and spark plugs. I think the +4 to -3 knock reduction is worth it.

so boostane is the best route instead of 100 octane? I have no cats so thats not an issue.

Barrel said:

Long term usage of an octane booster could have an effect on cats, but so might long term usage of forced induction, so...

Stoich of something like Sunoco 260GT 100 octane is 14.1 where standard gas is 14.7. So too much 100 and you could be throwing your car's fuel trims off and maybe cause a lean condition.

Something like Boostane won't do that.

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Stoich of gas with 10% ethanol is 14.1. Most gas has 10% ethanol (including the Sunoco 260GT), and the mustang from the factory is tuned for 14.1 stoich. It's the blend with ethanol that causes the change in stoich, not the octane.

erikkire18 said:

so boostane is the best route instead of 100 octane? I have no cats so thats not an issue.

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No, race fuel is better.

and mixing the race fuel and 91 won't be a problem or I won't need a re tune? sorry to keep bugging, just wana be sure before I put anything besides 91


thanks

erikkire18 said:

and mixing the race fuel and 91 won't be a problem or I won't need a re tune? sorry to keep bugging, just wana be sure before I put anything besides 91


thanks

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As already said, the stoich may be different and if you're not tuned for that you may run lean or rich and the ECU wont be able to correct for it. This could result in less power or it could also result in killing your motor.

I wouldn't do it without a retune. If you do retune, be sure to use the same mix ratio each time for the same reason as above.

It will be easier to run Torco. A retune for 100+ octane will result in more power though.

Look into meth injection. That's your best bet IMO if you want to help with octane and have no E85 available, rather than trying to mix 100 octane with 91, etc. I went from 16* timing @ 12psi to 21* @ 15psi on meth.

^as he said.... needs to be logged and tuned to be proper onrace fuel.

ahl395 said:

As already said, the stoich may be different and if you're not tuned for that you may run lean or rich and the ECU wont be able to correct for it. This could result in less power or it could also result in killing your motor.

I wouldn't do it without a retune. If you do retune, be sure to use the same mix ratio each time for the same reason as above.

It will be easier to run Torco. A retune for 100+ octane will result in more power though.

Look into meth injection. That's your best bet IMO if you want to help with octane and have no E85 available, rather than trying to mix 100 octane with 91, etc. I went from 16* timing @ 12psi to 21* @ 15psi on meth.

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As long as the race gas is unleaded with 10% ethanol, there will not be a change in stoich. You suggest methanol injection, which WILL change stoich because methanol is now added to the fuel mix. If you inject meth, I would definitely change the tune for it.

If you run race gas that is 14.1 stoich, it should be perfectly safe as long as it is well mixed. There is some concern that if the fuel isn't well mixed, that you may get 100 octane in the lines and your ECU will advance timing, then when 91 gets picked up and in the fuel lines, then the ECU may have to pull all that timing back quickly to avoid knock. In reality, I haven't seen this happen, but some people warn about it. I have personally run down to a 50/50 mix of Sunoco 260GT and 91 octane.

The octane booster should also be safe as long as it's well mixed into the tank. Add the octane booster to a tank right before you fill up and having it in there first should help mix it well.

As for whether you'll gain any power, that is completely dependent on the tune. If the tune allows for a lot of knock correction, then you may gain some timing. If the tune is already on the safe side, and doesn't allow for a lot of additional advance, then you will be just throwing money away and you won't see any gain, but it should still be safe. Octane shouldn't cause any change in fueling... you will not run richer or leaner, it will only allow changes in timing advance. A difference in stoich is what will affect fueling, and 14.1:1 race gas or octane booster should not affect stoich.