93 octane tune vs 87

Wow, interesting ways of explaining this so far. hehe In short, just like above, the tuner will advance the ignition timing (fire the spark plug earlier) which increases the cylinder pressures and makes more power.

You want to avoid auto-ignition of the fuel mixture (detonation). At high pressures and temperatures, the fuel can self-ignite, which is a cause of detonation (very bad to engines, and can be heard as an audible knock or rattle).

The spark plug fires long before the piston reaches the top of the cylinder. If it is fired too early, the pressures and temperatures will become so great that the rest of the mixture self ignites, resulting in detonation. The higher octane fuel is required to prevent this auto-ignition. As I said earlier, it is the increased cylinder pressures that produce more power.

Just to clarify, advancing the timing does not increase the compression. It increases cylinder pressures.

Also, the ignition timing has little effect on how much fuel is burnt, but rather when it is burnt. The earlier combustion is started, the higher your cylinder pressures can be, which makes more power (more pressure pushing the piston down).

There are volumes and volumes written about this stuff, and it is very interesting to me. I've spent quite a while in the engineering library reading about flame fronts and the effect of turbulence on the burn process. That little wall on the inside of the PI head is there for a reason.