engine RPM & MPG @ 65 mph

[DMAXchris]

If he had a six speed, it would have the +/- button on the gear selector.

Im at 1700 rpm at 65/70 and I get around 20 mpg. Before the tuner I think it was closer to 2000. I drove from Pittsburgh,PA to Sandusky, OH to Cleveland and almost made it back on the same tank with the cruise set at 72. IIRC it was around 500 miles. And I drove around cedar point and to the Rock&Roll hall of fame, so it wasnt all highway.

[New2DMax]

On a trip from Michigan to Colorado, I had cruise set at 70-72, averaging 2000 rpm. We got consistent 20-21 mpg the entire trip. I can get about the same driving 2 lane at around 60 mph, with RPMs running about 1700-1800.

[Ridin'GMC]

i have learned that now if your over 1600 rpm fuel economy is at the best because you are running at its peak torque. maintaining the engine's speed at peak torque will achieve the best fuel mileage. i found the engine spec for mine on wikipedia.

the 06 lly and the lbz has its peak torque at 1600rpms. the older lly ( 04.5 - 05) peak torque is at 1800 rpms. the lb7 is at 1800 rpms also. the LMM is the same as the LBZ. keeping the engine speed at that peak torque or close to it will achieve the best fuel mileage.

here is the site for each engine's spec
Duramax V8 engine - Wikipedia, the free encyclopedia

[moprr71]

SO you need to drive 50 mph to get the best mpg? I guess i need 3.08 gears

[Ridin'GMC]

not exactly, from 1600 rpms and more you will have the best peak torque. i will show you the chart of the engine peak torque. it is a LMM but it is also closely related to the 06 lly and lbz.

http://media.gm.com/us/powertrain/en..._SierraHDf.pdf

1600-3200 rpms on the 06lly/lbz/lmm will achieve optimum fuel economy. 1600 to 2200 rpms would be the best for fuel economy
BUT for the LB7 and the older lly, 1800 rpms to 2400 would be the best.

[KB3MMX]

Wow, I just got back from a long trip with my 07' LBZ and was starting to wonder if I was crazy to think my mileage was worse when driving slower!
Thank god there are others out there experiencing the same thing!
I have found my "sweet spot" for mileage was between 68-72MPH. Generally I get about 20-21 MPG when i run in that range. If I keep it right on 70, and watch my right foot, I have achieved 22MPG.
Anyway, on this trip I though I'd putz along at 62-65 MPH for a long stretch since I wasn't in a hurry... WELL....The mileage was much worse!!

Anyway, once again, I increased my speed to achieve higher MPG.
So much for going slower to save fuel !!!

[moprr71]

what about different fuel? Has anyone compared 15 ppm to 500 ppm and bio fuel? When I bought my truck in Kentucky and i was getting about 23 mpg with the remaining tank and then about 20 to 21 mpg the next tanks @70 to 75 mph.I think that there was bio fuel in the tank when i bought it because it got great mpg at 1st. Now in TX i got 18 to 19 mpg @ 75 mph and recently i put 285s on so the speedo is off.

[Killerbee]

If someone can tune to bring torque peak down to 1600, and drop the gear ratio (tires or gears), you could get 25 mpg highway at 75. The NBS has a bigger drag coefficient than the older ones, so it will be a little less. Not shabby for an 8000 lb truck.

[KB3MMX]

That would be sweet to drop it to 1600, I like low rpm torque..

**I was also wondering if anyone has done any electrical mods on sensors to get more MPG from increased timing advance?
**I was thinking of some sort of mod to make the engine think it's colder outside than it really is(IAT,EOT,etc?), thus giving a little more timing.......anyone??

[KSL667]

same here kb3mxx, my sweet spot is roughly 73mph. although the other day i switched my tune to tow/performance and dove 83mph while gettin 21.3mpg hand calculated