Originally Posted by lucid
If you get more hp from an engine by supplying it with higher octane fuel than it is designed to use that only means that the engine was NOT OPTIMIZED FOR PERFORMANCE. That would be the case for an Honda Accord, as the designers are keeping other variables in check and have a different intent compared to the M3 designers. We are talking about the M3 engine which should already be optimized for performance. Apart from that, the bottom line is the relationship between octane level and compression ratio; to truly take advantage of higher octane fuel, the compression ratio should be increased (apart from the minor tweaks you can do to engines which are not already optimized for performance.) We are not talking about any "modern BMW." Take an E36 M3, and fill it up with 100+ octane fuel. You will not see any significant improvement unless you change the cylinder piston geometry and alter the compression ratio.
dude... read the other posts. There is more to the equation than compression... there is also IGNITION TIMING!