[QUOTE=Sideways,May 3 2007, 09:44 AM] I've posted this before.

 

Slip, does combustion occur at a slower rate with higher octane fuels? And if so, could long term use affect (ie burn) the exhaust valves?

 

Yes, a fuel with a higher octane content will burn slightly slower than a lower octane fuel. Not enought to burn valves though. A very good question though.

There are several factors that can influence the octane rating. Many times the octane number is tweaked higher due to the additives in the fuel. Some additives artificially inflate octane numbers (ethyl alcohol for instance), while negatively effecting the BTU (energy) content. Additives can effect the burn rate as well.

Long term use of a good quality high octane fuel will not burn exhaust valves.
Running unleaded race gas in an otherwise stock S2000 won't hurt your car due to the octane content (depending on how they inflate and measure the octane number).
However, the lack of quality additives and detergents will cause damage to your car in the long run. Ensure you use a quality fuel treatment if you run unleaded race gas - like Redline SI-1 (my favorite). Road Rage posted some great info on fuel treatments in the oil journals.

Once again, most racing fuels are not regulated and have few or no detergent additives. Racing fuels are not designed or intended for regular street car use (most race cars are not designed to run for very many miles between overhaul either - food for thought).
I can't say this enough - NEVER use a leaded fuel in your S2000 - regardless if you have your cat removed or not. Aviation fuel or AV Gas (even if it states it's "low lead") is not an appropriate fuel for your car either.