Guess I'll stick with the 93!

 

I don't mind getting screwed by the BIG oil companies - I want to waste more money by using 91 octane in my truck, although, Ford says it runs the best on 87 octane.

 

I use a Diablo Tuner and run 91 octane. For my truck I get a pinging noise at part throttle when using 87 octane, even when using the stock ford tune or the 87 octane tune on my tuner... Havent gotten around to fixing it yet (already did plugs, COPS and alot of cleaning... I suspect the EGR). If I use a stock (87 octane) tune and put 91 in there is no ping and I get slightly better fuel economy. If I can ever figure out my problem though it will be back to a regiment of 87 octane.