Best approach to better mileage

MontanaMac · November 24, 2012

I spent a fair bit of time reading posts here and on a few other forums, with the intent of learning everything I can about increasing my truck's MPG.

Yes, I bought a truck--it is a heavy, boxy machine, and basic physics limits the distance I can travel on a gallon of gas. However, I was taken in a little by the window sticker which claimed an average 17MPG for combined highway and city driving. I think the only way I would achieve those results with a stock truck is to overinflate hard rubber tires and drive like a conservative Nun. For the most part though, no complaining, but desire to squeeze a bit more distance from a tank of gas.

From everything I have read, a custom tune will give me the biggest bang for my buck. If I am currently getting 14MPG with my 5.3L, and I keep everything else the same, including my driving habits, is it unreasonable to expect a 2MPG increase with a proper custom tune? I'd like 3MPG or more, but I am thinking that going from 14 to 16 is not too much to ask?

Popular opinion here favors Black Bear Performance. I also like what I've read about their customer service. Do you think there is any difference between a custom PCM tune and an AutoCal tune? Even though the AutoCal is more expensive, I'm leaning that way since I'd be able to experiment with different tunes, and restore the factory tune at will.

I probably won't bother with a cat-back system, since it seems like any MPG increase would be marginal. A CAI mod sounds to be even more questionable.

To sum it up then, I know my choice in vehicle, tires, and driving habits are costing me, but alternatives are not acceptable. Given that, I would still like to maximize my fuel efficiency, so I think a custom tune is the best first step. If I'd misunderstood something, I'm eager to hear other opinions.

8.1HD/ALLISON · November 24, 2012

The BEST thing you can do is change you driving habits. I doubt you will see a 2 mpg increase with a custom tune. Not to say you won't see an improvement, but it would be marginal.

scooby5121 · November 25, 2012

The rear end gears have a lot to say as well 411 or 373 or what your truck has.

Most likely you have the highway gear ratio so at speed your rpm are around 1800 at 60 mph,

Some around here like the air raid intake, with exhaust upgraded, I prefer neither,

With a custom tune running higher octane gas has me convinced with improved gas mileage,

Transmission also tuned with no throttle lag. And less surfing with gears also improved my power to the road,

My tune was not an out of a box tune thou,

Scooby

`

My 6L is leaned out to the max.

Carder09 · November 25, 2012

Though I have 3.23's, changing to 4.10's soon, with my tune, I am getting 18 MPG going 80+; when I keep it below, I see well into 20+. I also have a cover on the bed so that probably helps a tad bit also.

kstruckcountry · November 25, 2012

With a cover on my bed, I got 18.5 @70.

With the front end replacement, bed full of stuff (covered), and Magnaflow, I got 18 @70. Haven't done a long highway drive without a load. Regular driving in town and what not I get 15.

EDIT: I have 3.73 gears.

SouthCo · November 25, 2012

The BEST thing you can do is change you driving habits. I doubt you will see a 2 mpg increase with a custom tune. Not to say you won't see an improvement, but it would be marginal.

I agree. Your driving habits will yield the biggest increase in MPGs and it's also free. I have a custom AutoCal BlackBear tune and really like it, but you are not going to get 2mpg more with it with all else staying the same. You are not going to get that with any tune. I also have the 5.3 by the way...

99silveradoz71 · November 25, 2012

I'll agree with the others, a custom tune is going to improve the driveability of your truck more so than improving your fuel efficiency.

music · November 25, 2012

OEM tuning is geared towards efficiency, emissions, and protecting the drive line. Tuning tends to get power to the road quicker, and usually enables fuel enrichment sooner. Neither of these will help mpg, but they do help with smiles per gallon.

TimmyG · November 25, 2012

I didnt see details but my 11ccsb with 5.3 i avg 18mpg

Sent from my ADR6400L using Tapatalk 2

MontanaMac · November 25, 2012

Hmm, I see. You gotta admit, there is a lot of conflicting info both here and other places.

I will not disagree in any way that changing my driving habits would have the biggest impact on economy. I just know myself, and know that ain't gonna change. At the same time, I'm not a crazy kid, rocketing away from stoplights, and accelerating as fast as possible. My thinking was that a custom tune could deliver both increased efficiency along with a mild performance gain. A small performance gain might allow me to put a little less pressure on the far-right pedal.

I used to have a 2500HD Duramax, and I used a Hypertech tuner that would give me three HP boost options. I tried the lowest one a few times, thinking it might offer better fuel economy. After long-term testing in many different conditions, it turned out that the most HP gain option also gave me the best fuel economy, just because I didn't need to floor it to pass another car or zip up the on-ramp. I was hoping that a similar principle would apply to the gasser. (BTW, it is really difficult to step down from the torque of a Duramax to a 5.3L gasser).

I forgot about gears. I have 3.42 in mine, so I am about 1800 when going 75mph in 6th gear. Maybe going to 3.73 or 4.10 would help with city mileage since it would bog down less from a standing start, but then I'd be at much higher RPMs on the highway. Just for reference, where I live you don't go 60 or 65 on the highway. The 2-lane, 2-way is 70, and the interstates are all 75---you get run off the road if you do less (not that I would anyway :-)

If I put the truck on cruise at 75 on the interstate, it doesn't take but a slight grade, or a little headwind to make it down-shift. I am a bit disappointed in that, but maybe taller gears would help that out, and get me better MPG overall, even if the RPMs were up more.

Thanks for the info and help.

8.1HD/ALLISON · November 25, 2012

Don't get me wrong, a custom tune will probably help 1/2- 1 mpg maybe? I saw an improvement with mine. (8.1L) I also adjusted the shift points as the Allison tends to wind up a little higher before it shifted. If you are gonna tune, custom is the way to go, just don't be disappointed if you don't see big numbers.

MontanaMac · November 26, 2012

I will admit that I tried a Predator when I first got the truck. Not surprisingly, I didn't see any improvement in MPG using their canned economy setting. I also tried their performance setting and thought that maybe, MAYBE, I felt a bit more jump from a standing start, but not much. Summit Racing refunded my money without any fuss.

Now the truck has 16K on it, and the mileage improved a bit just after break-in.

Gearing may be as much of an issue as my driving habits. I just calculated the actual numbers, and with my 3.42 ratio and bigger tires, I bet my in-town mileage would improve with a higher ratio, and maybe the truck wouldn't downshift quite as much on the highway when faced with a slight grade or headwind. But, with a 4WD, changing gears is just not an economical option--I can buy a lot of gas with the cost of parts and gear set-up labor for two axles.

Because it is still relatively inexpensive, I am going to talk with the folks at BB, and probably end up with an AutoCal loaded with some of their custom tunes. I intend to be very careful in logging mileage, type of driving, environmental conditions, elevation, fuel octane, and tune parameters, and generally be as scientific as possible to determine what, if any improvements I get. I will reply to this thread in a while to report my findings. If BB or some other shop has already done something like this under controlled conditions, I haven't seen it. Obviously, I cannot be as precise as a shop using a calibrated load and a dyno, but I'll do my best.

Thanks for the help--not exactly what I wanted to hear, but not surprising either.

8.1HD/ALLISON · November 26, 2012

Sounds good! Let us know the findings.

99 2500 · November 28, 2012

I went from averaging 14 mpg to 16 mpg in a 2002 Tahoe by changing the crank pulley to the 25percent underdrive pulley and replacing intake tube with the airaid replacement tube.

mymaggiebell · December 2, 2012

91 octane stock compared to justin's auto cal tuned with 91 octane, i am getting 50-60km more per tank!! just ordered an airaid mit, off him, and would be curious if that helps, although i am not holding my breath.....