Originally Posted by Will2329
So currently I am running the performance tune and I have a quarter tank of regular gas in my car, and I think am ready to fill up with 93 octane next time, and load the race tune. My question is... Do I have to run my car to like 20 miles to E then fill up and load the tune? My concern is loading the tune and there still being a little regular gas in the car and it messing something up...
It's easy to dilute the higher octane gas when filling up on an old tank of 87octane. To play it safe, I always suggest running the car until the gas light comes on and then fill up on 93 octane. For the first full tank of 93 octane, keep the 87octane tune loaded. Run this first tank of 93 down to an 1/8 tank or so and then fill up on 93 octane again. For the second tank of 93, you should be plenty safe to switch to the 93 octane tune.
I know it's a little bit of a process, but if you do it this way you'll never run into a problem with poor octane gas being used with the wrong tune!