Fuel mileage tracking for tuned 5.7L - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 29 (permalink) Old 12-22-2010, 05:40 PM Thread Starter
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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)
Superchips Tuner

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.
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post #2 of 29 (permalink) Old 12-22-2010, 05:54 PM
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Thanks for the research effort. It will be interesting to see more results.
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post #3 of 29 (permalink) Old 01-26-2011, 04:36 PM Thread Starter
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Looks like I was wasting a lot of money with the 91 Octane.

My gas mileage stayed right around the 13mpg mark for my daily commute with 87 in the tank. Worst I saw was 12.7 (when stuck in a lot of traffic) and there were days when it was hovering around 13.2.

I switched over to 89 Octane yesterday... so we'll see if this changes it at all. I'm hoping for a solid 13-13.5, that would be nice

Summary:
91 Octane w/91 Performance tune = 12.3 MPG
87 Octane w/87 Octane Performance Tune = 13 MPG
89 Octane w/87 Octane Performance Tune = TBD

** This is with my normal daily commute. Highway gas mileage seemed to have improved also (around 16) but I don't do enough highway traveling to know for sure if there was a change.
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post #4 of 29 (permalink) Old 01-26-2011, 06:01 PM
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Good write up, Matt!! We started running 87 in my wife's 08 Hemi Charger(which got traded for my jeep), and other than some barely noticeable power loss, it was fine and mileage appeared to be same or slightly better.. I've tried it in the Jeep, while it's not "tuned" for 87, I'm not seeing any ill effects..Keep us posted, as I'm considering buying a tuner and wondering if it's worth it for the limited amount of miles it gets driven
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post #5 of 29 (permalink) Old 01-26-2011, 06:28 PM Thread Starter
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I bought the tuner primarily to adjust the speedometer for the increased tire size and for a few of the standalone features that come in handy for offroading or maintenance (like being able to increase the idle RPMs for running a winch or to heat up the engine quicker after a coolant change).

I've heard of people getting better gas mileage with these performance tunes over stock... and when i was seeing 11 on occasion and never getting above 12.5 i decided to start this little experiment. I'm a bit happier with 13
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post #6 of 29 (permalink) Old 01-27-2011, 10:04 AM
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Join Date: Dec 2010
Location: Lisle, IL
Own a Commander?: Yes
Model year: 2007
Trim Package: Overland
Power-Train: 5.7L V-8 Hemi
4WD
If 4WD - system: QD-II
Current Mileage: 126000
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Obviously if you're talking about cost, we need to factor in the cost of 87 vs. 91. And for those looking solely for mpg increase, you need to factor in the cost of the parts that save you fuel (programmer, intake, exhaust). $1000 is a lot of extra gas.

I wish the programmer had a "Super Econ" mode that kept the engine in 4 cylinder mode longer.
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post #7 of 29 (permalink) Old 01-27-2011, 10:29 AM Thread Starter
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I believe there are "economy" tunes that you can get for these.

But to be clear, i did not buy the programmer for mpg.

All i'm doing here is recording what my actual MPG figures are with the different tunes and octane levels.

I've seen multiple threads where people claimed that with the 91+ tunes they were getting enough of a MPG increase to offset the price of the fuel. That obviously isn't the case for my vehicle/commute.

There's also been a lot of questions about whether to run 87 or 89 in the 5.7L. Since there's not a clear answer to that, im doing my own test to see if there's an effect on MPG between the two. (Edit: if the 87 and 89 yield the same results, i'll probably keep running 89 per the owners manual since it may actually make a difference under hard acceleration or towing; neither of which I do on my daily commute. Well... i do hit the gas once in a while... but not every time the light turns green)
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post #8 of 29 (permalink) Old 01-27-2011, 01:49 PM
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Join Date: Dec 2010
Location: Lisle, IL
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Model year: 2007
Trim Package: Overland
Power-Train: 5.7L V-8 Hemi
4WD
If 4WD - system: QD-II
Current Mileage: 126000
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I just got mine updated, so I'll be checking out the new features today.

The cost vs. mpg thing was just a word to the wise.
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post #9 of 29 (permalink) Old 02-11-2011, 10:33 PM
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Matt, good numbers man. Our 2010 Hemi is getting considerably better mileage than that though. With the wife driving it mostly, it's getting 15-15.5 in and around town. On the highway, if the wind is mild and without too many hills, it gets 19-19.2. I hand calculate mine at every fillup, and it is almost always within a couple tenths to the EVIC. It's still on the factory 29" tires, and has the 2.5" RC lift and a Predator tune on the 87 tune and a drop in K&N. After 4700 miles, the EVIC is showing and average of 16, which I don't complain a bit about for a heavy 4wd suv.
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post #10 of 29 (permalink) Old 02-12-2011, 02:12 PM
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Join Date: Dec 2010
Location: Lisle, IL
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Model year: 2007
Trim Package: Overland
Power-Train: 5.7L V-8 Hemi
4WD
If 4WD - system: QD-II
Current Mileage: 126000
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Quote:
Originally Posted by JRod View Post
Matt, good numbers man. Our 2010 Hemi is getting considerably better mileage than that though.
The 2009 HEMIs had some updates including staying in 4 cyl mode longer.

Quote:
The 2009 Jeep Commander will arrive in showrooms this September with some welcomed new features. The current 5.7L Hemi engine will be replaced by the all-new 2nd generation 5.7L Hemi. The new Hemi offers variable cam timing; a higher compression ratio; higher-flowing heads, intake, and exhaust; and an active intake manifold that switches from long runners to short runners, to optimize the engine for either better high-end horsepower or better low-end torque. Horsepower output is expected to be around 370, with torque numbers near 400.
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