Quote:
It is a waste of money over purchasing 91, but it won't generally hurt the engine. If you have a misfire in cold weather, stop using higher octane fuel, as it can cause the misfire.
The biggest mistake made is that people assume that a higher AKI is somehow better. If you have a sufficient AKI to resist predetonation, anything else is lost. Your engine can't tell the difference.
|
This needs to be refined further: my understanding is that you want to use the LOWEST octane possible to which your car's computer can calibrate to prevent knocking.
Obviously, in a car without a knock sensor -- like my old Mustang -- 87 would prevent it from knocking just fine. Hence, using 91 would have actaully been bad -- carbon deposits in cats, etc -- until I added a chip recalibrating the engine for 91.
However, in our X's, I imagine the computer can calibrate itself all the way up to Euro-calibre fuels of 100 octane or so. Let's assume for sake of argument, however, that our computer could only handle up to 98 octane. Well then, I'd say put in 98 -- but do *NOT* put in 100!!
For instance: on May 10 when my Dad and I head up to Thunderhill Raceway in Willows, CA, we're going to fill upon 100 octane at the track because my understanding is that our X's *CAN* calibrate for 100.