Originally Posted by
crash
Rev2xs-The only thing that a higher octane fuel does is allow you to run more compression and/or more timing advance before detonation occurs. The notion that you could run a leaner mixture may be slightly true in that the leaner mixture could be run with a higher octane fuel before detonation occurs, due to the higher octane of the fuel, but you will not build more HP at this margin of running too lean. Most modern engines, like the LS, have knock sensors and the computer just retards the ignition if knock is present. That is why the LS engines run a relatively high compression ratio stock. The computer allows this by retarding the ignition to just below detonation levels. This also makes it so that you can run 87 or 91 in your car and not have any damage to the engine. 91 SHOULD make more power because more timing can be put into the ignition, but the factory computer should automatically take care of this issue of maximizing whatever fuel you are using. You CAN mess with these maps as well, but it can get expensive quickly if you map the knock retard scale wrong.