What octane fuel to use?
Ok, so my mod list is in my sig and I'm wondering what octane I should be using. At the moment I'm putting in 89. Even though I don't have a tune, should I be using 91? My gas mileage is pretty decent, but I want to know if it would really make that much of a difference before I spend the extra few cents for 91. Thanks
DD: 2003 Ford Focus ZX5-65mm TB, Intake, Long Tube Header, 2.5" exhaust, UDP, Tom's Tune. Almost 200k miles and still running strong!