Quote Originally Posted by Dyno Brian View Post
That is correct. Some pcm's will also use just the low octane table if the car is in reduced power or if there is a sensor failure. On LS engines if you unplugged the maf and force it into speed density all the time the car will run on the low octane table. Custom Operating Systems correct this with certain cars. A lot times tuners will copy the high octane into the low octane table so timing is repeatable. Obviously a good tune is important at this point to keep knock retard at a minimum.
"a good tune" is far less important than a good running motor.