The Mystro S4

What does a APR 93 chip change to the car to get the extra HP?I was asked that and I couldnt say.

JustJeff

You could say "change in the ECU profile that allows the engine to make use of the extra octane power of the burning fuel", but that's a Reader's-Digest response.

What exactly was changed from say the 91 program is a guess, IMHO.

The Mystro S4

APR really doesnt say on their web page.

FasTTr

APR told me main difference between 93 and 91 program was tweaking the timing advance.

FelonyRuckus

FasTTr is right, higher octane allows engine timing to be advanced even higher...