omg, how are you going to pre detonate when you are off the throttle? unless you are running like 30 year old mexican gas and your going like 2 MPH in 100 degree weather pulling like 5000 RPMs constantly. And in that case your freaking engine would be running backwards or some crazy sh*t becasue your piston would be like 2 inches from TDC when it pre detonated while you are on the throttle giving it actual load. Which is when pre detonation actually happens. Why would you even run reg. octane in a air cooled sort of wanna be racing engine? And dont say cuz you cant afford anything else, thats a stupid answer