I have alway's used 93 Octane and the car has never overheated.It did have a problem shutting off but I think that was due to the MSD Ignition.I had to run a toggle switch to the Regulator because I needed the switch to turn on the Alternator.Now if I didn't have that switch to the Reulator the car wouldn't shut off if i turned the key in the off position.I don't know if I have a wiring problem or it was The MSD ignition but the only way I can shut my engine off is by the ignition toggle switch??