compression ratio
Octane is a fuel's ability to resist detonation and/or preignition
It comes down to your compression. If don't have a really high compression head the extra(RON) Research Octane Numbers do you no good. Not saying that your ski is, but a lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design. At high RPMs, there is very little time (real time - not crank rotation) for fuel to release its energy. Peak cylinder pressure should occur around 20° ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure (lower top end).Unless you have a heavily modded machine with ultra small domes, leave the high octane stuff alone. I still run 93 pump with an 849 stroker at 190 psi. The burn and wash on the piston head tells you your machine is set up properly and mine are looking normal. If you don't have one, pick up an aftermarket head, it's the best bang for buck upgrade for any ski.