SlowHand

I'm going to do a 91-Octane tune but I've been running 87. I let the gas drain to < 1gal and then refilled with 91, but I do not want to experience any detonation when I install the 91-O tune so can anyone advise as to the best way to make sure that I'm running "pure" 91? I know this is a slightly nervous question so please bear with me.

boomerman

Run the tank down to E and fill it up with 91 you will be ok.
I switch tunes all the time and I do not have any problems going from my 87 to my 92 tune by doing it this way.
Actually I have found I can run my 92 tune using 87 octane gas, and get no ping or detonation.
I do notice a decrease in performance running my 92 tune with 87 gas but I can still run it with no problems.

2oo5stang

If you had 5 gallons of 87 and the rest is 91, you'll still be fine.

GT Newbie

I had slightly more than 1/2 tank of 87 octane and toped it off with 93 right before my tune yesterday, and didn't have the slightest problem.
The installer told me not to really get on it to test maximum performance until the tank was all 93 octane, but even at half & half it was GREAT...!!!

Arwing

When are you doing then tune? just drive till empty with 87 then fill up with 91 then drive till empty with that then fill up again with 91 then tune it. wont hurt it.

SlowHand

That's reassuring. I ran it down to less than one gallon of 87 then filled up with 91. As Arwing says, I'll go for one morerefill from empty and then it should be safe to upload the newtune and drive it.

Thanks guys.

Goldenpony

You're fine. Remember, your engine has a knock sensor in it, if the sensor feels a knock (it acts before you'd ever hear it), it will ease back on the timing to protect you. No worries mate!

ANBAUTO

well if you got 1/4 of 87 just fill up with a few gallons of 100 and it will equal out to 91

Dumpweed

haha...man i love this site.

ANBAUTO

im not sure if your pokin fun but thats what procharger says to do as well.