Fuel mileage tracking for tuned 5.7L
The point of this thread is not to argue about what octane to run or whats best, it's simply a case study that others might find helpful.
Some details on the Jeep:
2007 Limited Hemi QD2
245/70/17 General Grabber AT/2s @35 PSI
~30k with fresh plug change (used OEM coppers w/correct gapping)
I have a consistent 25 mile round trip to work that has 6 traffic lights. Street speed limits vary from 35 to 50.
With the 91 Octane performance tune and running top tier 91 octane gas i was getting 12.5 MPG.... maaaybe would see 12.6 if I never got stuck at a red light. This has been consistent for the past 3 months (when the Jeep became my DD).
I decided to re-tune my Jeep this week to 87 Octane.
First thing, i knew my speedometer was slightly off with the 91 tune. I put in the calculated tire size of 30.5 and i originally tuned it and my GPS always had me going slower than my speedometer said. When I re-tuned my truck with the 87 octane, i measured actual tire height and got 30.0 (damn near exact). My speedometer is now correct.
Adjusting for the slight difference in tire: (30/30.5)*12.5 = 12.3
So for the comparison, my 91 octane tune was actually yielding 12.3 MPG since i was not actually traveling as far as my odometer thought.
After 3 days of commuting with the new 87 Octane tune and running 87 from the same gas station, I'm getting 13.1 MPG.
One note: when i filled up my tank took 13.5 gallons of 87, the remainder in the tank was 91. So i'm not running pure 87 yet. I'm interested to see how my gas mileage changes with subsequent refills.
I'm off the rest of the week but I plan on continuing to run 87 to see if anything changes. Once I have been running 87 long enough to really get a solid feel for my actual MPG, i'm going to start running 89 to see if there is any effect.
In any event... i can't remember the last time I saw the number 13 in my MPG screen. I have however seen 11 on occasion; sometimes I just catch all the red lights for an entire week.. sucks when that happens.