525 fuel tank is 21.37 gallons. My fill up today was 17.1 galllons (needle hit empty... apparently a little pessimistic). I tuned my ECU more lean during cruising and light load (though I can spare to go leaner, so I will) with an AFR of about 14.5 - 15.3 while cruising and managed 339 miles to the tank. Apparently I had about 4 gallons left in the tank but my gauge/sensor sucks, but anyway, that comes out to 19.82 mpg in my car (combined highway and shorter city travel) which is honetly ridiculous compared to what I used to get.

I used to get anywhere from 220 - 240 miles per tank when I had my other tune running - this is just great. In theory, if I ran the tank down to having only a gallon left, I could do 396 mile per tank. That's !

Tuning this stuff is fun and rewarding!