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What are you getting for Fuel Mileage?

4K views 29 replies 13 participants last post by  TheBac 
#1 ·
Hey guys, a friend of mine is looking to get a used diesel pickup and wanted to know what the Duramax gets for fuel mileage on the highway. He doesn't tow anything so he is looking for normal highway mileage. So what do you guys get? Also let me know if your truck as a chip/tuner or if it is stock.

Thanks,
Ryan
 
#4 ·
i only get 12 12.5 around town and on highway empty, loaded is a about the same as long as i keep it under 65mph or less. no tuner just magnaflow exhaust system and k&n filter, the only reason mine is so low is because of the lift and tires,the bigger you go the worse your mpgs the one thing that has bumped up my mpgs is that lucas fuel additive,but it just ends up pretty much payin for itself although it has also bumped up the hp a little not to mention its helping protect the top end from the lack of lubercation from the ultra low sulfer diesel.
 
#5 ·
mckey73 said:
The lly's are a bit worse,
I was just thinking we were overdue for another economy thread.:shrug:

Today, I logged 29 mpg 52 mph avg, straight line flat, no stopping, 1400 rpm (Bigger tires). 28 mpg one way, 30 mpg the other, 30 miles. But that is unrealistic, and not a representaion of how people use it.

LLY, my tune.

The killer is having to stop and start an 8000 lb truck. If you are good at planning stops from a distance you can increase mpg a lot. Too bad we can't collect the energy of braking like a hybrid.
 
#6 ·
well... I wish I would get even only 18mpg on the highway with my 07 Classic cc. Last time I looked I got 15.5mpg on the highway and 13mpg jiggin around. That is with no tuner and 265 BFG all terrains on stock rims.
 
#7 ·
mckey73 said:
I get about 17 to 18 empty on the highway, about 12 to 13 if hauling my 24' bumper pull. Around town running a pretty good tune I get 20 to 21. The lly's are a bit worse, with the '05 2wd cc/sb auto my dad gets about 15.
Wait I am a little confused here. You get 17-18 mpg highway and 20-21 city? You getting better mileage driving in the city than on the highway, is that right?
 
#11 ·
Sorry about that.

But you are the best city mileage report I have ever heard. Stock or tuner, the best I have heard of was 15. Most get like 12. You are 60% better. Does your in town driving, involve urban starts and stops, or rural roads with no stop signs? What size tires?

IOW, how can we all get 21 mpg in the city?
 
#12 ·
First off, I have an '02. My dad has the lly, not me. When I drive in town I have the average number of stops and starts (austin tx). Most of the speed limits are 35 to 40, which I drive in 6th gear. Currently I have mostly bald 285's. oh, and it's a 4wd. I have heard of many people getting in the 20's, but not with an lly. I also run a ppe tuner on level 5 unless I'm towing or racing.
 
#13 ·
What conversion factor are you using for the 285's? How much noisier is your PPE over stock (timing)? 2 seater?

Note: I am not picking apart your assertion, I have done some playing around with economy and am learning here.

Your low rpm technique is something I have tried on the allison, but it won't stay locked up below about 50 mph.
 
#14 ·
With the tuner I'm able to change tire height, which I have done by taking an actual measurement. Then just reset the odometer when I fill up. I have checked the speedo against the two gps units I have and they are both right on up to 100mph (thats as far as the speedo goes).

Currently I have an airaid intake, straight pipe and a new DD clutch. So I can't really speak for how much noise any particular tune is adding. While sitting idle, in neutral you can definately notice more vibration. The biggest difference in engine noise came when I added the intake and removed the big plastic thingy that has the 6.6 logo on it.

Hope this helps!
 
#16 ·
Mine is similar to mckey73's... ex/lb 4x4, gets 20 around town with lots of stop and go, never over 55-60mph, I shift between 1500-2500rpm usually, have 265's, and have never dropped below 11mpg towing heavy. (6.5 got 8...) I have never had the chance to burn a tank on the road empty so I can't say if I get better or worse. One tank that was mostly highway miles was headed upward of 24 I'd estimate, but I finished it off towing. (still averaged 19mpg)

IMO the ZF6 has the edge in the fuel economy game.
 
#17 ·
I get right around 15 MPG city and the best I have had is 20.44 highway,(55-60MPH). I run 265 dueler's and my edge is on 1 normally. MBRP Exhaust SB/CC w/ 4x4
 
#18 ·
I'm new to this site, and found it looking for people who know the best way to program my 'puter. As far as mileage on a completely stock 2002 GMC Sierra 2500HD 4x4 (not Z71), I get anywhere's between 16-18 mpg mixed highway and in-town, and highway only I nac easily go 500 miles on a single tank- which I believe is a 24 gallon. Stock tires, program, everything right off the dealership. From what I hear, the 6.6 is a great engine- but that's not saying much.
Also- which companies would anyone in here reccomend for programming my computer for a good mix of fuel efficiency and still decent towing? Banks looks like it's the most powerful so far, but is it worth the money?
 
#19 ·
I wouldn't use any of the handhelds for towing. I seriously believe that they suck for heat soak towing conditions, where timing is way overadvanced for the conditions.

The handheld manufacturers don't adjust ANY of the tables meant to compensate for sustained workloads.
 
#20 ·
With twins I have seen as high as 29 MPG but average on the highway 25-26.
 
#21 ·
Nasty Girl said:
With twins I have seen as high as 29 MPG but average on the highway 25-26.
Wow. maybe I should have bought the D-max
 
#23 ·
I honestly believe his tuning has more to do with economy. The twins don't help unloaded economy, there is no boost requirement at all for unlaiden cruise, the VVT air restriction is very small at these low low air flows. Just my thought on that. I routinely get mid 20's on some highway trips. Get that cruise timing advanced with EFILive.
 
#24 ·
I agree don't go with twins if you are only after milege. Tuning is 80% of it, however a diesel engine that breathes freely in and out will be more efficent. Twins will only help with milege under load this is true....but what the hell twins sound cool too! :Thumbup:
 
#26 ·
No secrets here. I will tell you what I have done to my engine if that will help.

I run a 6" intake, to my big turbo, 4" piping to second turbo, external regulated wastegates, 3" intercooler piping, banks technicooler, along with a custom 3" intake bridge (Stock is 1 7/8" I.D. IIRC), ported and polished heads, larger intake and exhaust valves, 5" custom downpipe and 5" custom dual exhaust.
 
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