Originally Posted by DoomsdayFAN
I'm talking about getting a tune for it. Are you going to get better gas mileage with an 87 tune, or are you going to get better gas mileage with a 91 tune? In other words, I'll be getting a tune either way, but which tune will get me better gas mileage? 87 or 91?
I believe it depends on the kind of tune you want, you can tune more for performance or economy. 91 burns a little smoother than 87.
Does the ECU in the focus not adjust to octane ratings like other cars? Example, my V6 accord will adjust to different octanes and advance or retard timing to compensate, but switching from one to the other you need to go about 500 miles on the certain octane before the computer recalibrates for the octane. Running 91 instead of 87 will get rid of pinging and get me slightly better milage although on 87 I can average 35mpg on the freeway (about 1 mpg better with 91). A honda engineer has said running 91 instead of 87 will give you a 10hp bump in the accord as well. All this without a tune.
Thanks for bearing with me, trying to expand the knowledge of my vehicles.