M3iRiSH

If the ECU did not increase timing, and you added a high octane fuel, you would have a richer exhaust emission and have higher EGTs. It takes longer to burn a denser fuel, so you generally need to increase timing BTDC with race fuels.

Flyboy

that race gas density decreases as the octane level increases.

And though the two, burn rate &amp; octane, are independent, there is usually a correlation between the two, with higher octane ratings having faster burn rates.<ul><li><a href="http://www.sunocoinc.com/site/Consumer/RaceFuels/UnleadedFuels/">Sunoco Unleaded Race Fuel Properties</a></li></ul>

M3iRiSH

This is because you need to start the ignition at an earlier point to get peak pressure at the correct deg of rotation of the crank. The burn takes longer, so start the ignition earlier.

If timing is not increased, you don't get a full burn, hence causing a rich condition at the tail pipe.

Flyboy

really want a longer burn, that just spreads the pressure rise and fall over a larger crank angle. There's an ideal crank angle range, that is fairly narrow, where the cylinder pressure is delivered with greatest leverage to the crankshaft. Outside of that range you're losing potential power.

If you've got a race engine running at 10,000 rpm you don't want to be advancing engine timing out to 40 degrees. The burn would take so long that the peak pressure point would barely qualify as a peak. The race fuels burn faster, so the pressure rises quickly, when the crank angle is within the optimum range, even with the very high rpm's.

You have the right idea about using the timing to adjust the PPP, but you're mistaken about the burn rate of race fuels.