I have been running a canned sport-87 octane tune on my truck but i've just recently filled up with premium gas 91 octane and wondered if having a half tank of 87 and half 91 would do any damage if I switched my tune to the sport-91 octane while it still has 87 mixed in. Just random question hoping someone can steer my in the right direction. My programmer is the Banks Automind.

 

would be best to run the tank low then fill with 91 before going to the 91 setting. I wouldn't run it now with a mixed tank.

 

That's what I was thinking but just wanted to hear it from someone else. Thanks! I take it running the 87 tune with half 91 wont harm anything either? Lol

 

If you switch it and hear pinging, it is due to the lower octane. If you switch and don't hear pinging, you are good to go.