I have a 2002 A4 Quattro 1.8T which requires at least 91 octane gasoline. First of all any ethanol free gasoline is hard to find and most 91 octane gas is supplemented with 10-15% ethanol. What are the consequences of ethanol and would I be better off using an 87 or 89 octane fuel with an octane booster. I was fortunate to find some 91 octane alcohol free gas once while traveling and the fuel economy was about 10% better than usual.

 

I would just switch to 93 and forget about the implications of using lower grade / higher ethanol content gas. Better fuel economy, smoother running, and engine longevity are all a byproduct of using better gas.

 

I have never seen 93 octane fuel where we are in eastern NE and even the 91 "premium" has been tweaked with ethanol. My question is this: Am I better off with 91 octane E-15 or should I use pure unleaded regular with an octane booster? Those appear to be my only two choices.

 

Ah, got it. I would use a high quality octane booster and the pure regular unleaded, just to keep the ethanol out. See how it runs on a tank and go from there.