I have an 11 non pp and will be buying a 91 octane tune, 3 bar and t-stat soon. Have been running regular 87 octane since I got the car.
So. Should I fill up with 91, run it down, fill up with 91 again just to remove all 87. Or, say I have 1/8 tank of 87, can I just fill the remaining 7/8 with...