mtroxel

You're not getting detonation because engine management is getting info from the knock sensors and retarding the spark for the lower octane fuel. Retarded spark, less efficiency. Don't assume that 93 octane is all gone to waste. The ECU doesn't know octane numbers, it just sets the spark for the most efficient timing it can without knocking.

mrtoo1

I agree....however I cant see there being that big of a difference that would effect efficiency to say Im wasting money using 89...if 89 is 2.85 and 93 is 3.30. and the engine is designed to run on 91 will the ecu advance timing to run with the 93? If not then I'd be wasting money as well. To say because 89 may not be as efficient and to sell the car because 91 is not available seems a little extreme.

mtroxel

I agree, and I'm not the one who said that. And I don't know at what point the extra efficiency of high octane pays for the $2.50/tank increase. But I also don't think it's a waste. I spend $1,000's every year to make that car run well, what's another $2.50/tank when I get at least some of it back, get better performance, pollute less and keep a little more money out of the hands of Muslims.

mrtoo1

I know you didnt say sell the car that was directed to the person that said it......The question is which is more of a waste of money using 89 nad not having the engine run as efficiently or using 93 and maybe not running any more efficiently that running 91? Because I doubt that the 93 will make the engine run more efficently or get any improved performance.....Also the other question is adding some octane boost to the 89 to bring it up to 91.