Back in the 70s I rode 2-stroke bikes and used lawn mowers with 2-stroke engines. I really liked 2-strokes because of the high power to weight ratio. Interestingly, all the manuals for the bikes said not to use high octane fuels for the best performance. 89 was usually suggested. I did stuff to my bike engines to get more power. Things like porting and raising the compression and using expansion chambers. I had lots of success increasing HP and RPM. The reason for the low octane rated fuel, I was told, was because the gas would burn faster and this was necessary because as much power as possible must come before the exhaust ports are effectively open. I know, effective port timing can be changed by the use of expansion chambers and intake manifold changes. Exhaust and intake resonance can be used to control the fuel/air mixture flow into and out of the cylinder. RPM is part of the way resonances are controlled. Nevertheless the physical location of the ports cannot be changed like variable valve timing in a 4-stroke. The long preamble is just so you know why I am curious why so many folks these days talk about how higher octane is desirable in 2-stroke engines. I saw this once again in the recent E15 ethanol thread. Octane does not add heat energy, it just helps control burning. Higher octane being slower burning. And adding ethanol, while increasing octane, actually lowers the heat energy of the gasoline and ethanol mix. But by increasing octane the compression ratio can be raised and this will allow getting more energy from the fuel. Which in 4-stroke engines is usually a good thing.
Eric
