RRocket said:
Yes and no. On a particularly hot day, the car is more likely to pull out timing from detonation, especially if he's running 87 octane to begin with. So 100 octane would be beneficial since it would allow for max advance. On my friends Grand National (he's set up for data-logging) he put in 87 octane just to see how much timing it would pull out and it was over 15 degress compared to 94 octane! So in certain conditions, higher octane will make a difference..
87 octane in a turbo car is a deathwish
i agree that running lower octane then the factory recommends is going to cause the car to detonate and pull timing
but on a car tuned to run on 91 octane (which is what is recommended for an mkiv) running 100 or more will not yeild a benefit because the stock computer will not give it timing
example is my supra... i was able to give it some timing on 93 octane in 90 degree summers and gain hp... and i still have a conservative tune
the only difference between my race maps and my street maps on AEM are timing... the c16 maps have significantly more timing and slightly less fuel then my 93 octane maps