[Unichip Jack]

Thanks for the PM.

The main difference between high and low octane maps is the amount of ignition timing added to the tune... and that's strictly a function of the amount of ignition timing the fuel supports.

High octane fuel burns slower than low octane fuel so you can start the combustion earlier (more ignition advance) to get a more complete burn and make more power. If you use that same amount of timing advance with low octane fuel, the combustion completes too soon and you get "knock."

The OE computer will detect the knock and retard the base timing which eliminates the knock but will generate a flashing CEL and a misfire code. Because of that, you won't "hurt" anything but you will lose quite a bit of power.

The OE computer typically pulls "too much" timing and you'll end up with less total timing (OE ECU + Unichip) than if you ran the low octane Unichip map... in other words, you'll probably end up with less power from the low octane fuel/high octane map than if you ran the low octane fuel/low octane map.

Please let me know if you have any other questions.

Cheers,
Jack