At what RPM is the Duramax making peak torque?

[Mark Rinker]

After reading the latest September article using a Penninsular built 6.5, am wondering where the Duramax should be running to achieve its best fuel efficiency.

Would this figure be identical for stock LB7, LLY, and LBZ engines, or would it vary? What effect would a 40hp tow tune have - higher or lower rpm?

[Freeman777]

I just returned from WY towing a 15k (approx. 22.5k including my 2004 GMC K3500 CC 4X4 LB) 36ft 5'er, about 628 miles. Mileage varied from 11mpg in the tough stuff to 13.4 clear sailing. I make decent time traveling at 67mph and 2000 rpm will pull respectable hills without shifting out of OD. I just turned 50k on my truck and tow about 15-20% of the time. I used to tow at 72mph, but I'd rather have the increase in economy, than get there a little sooner. My trip through the Pacific NW in July/Aug, (2,700 miles) diesel was as high as $3.69.9! Yesterday, I paid $3.09.9 in St. George,UT and back in Vegas, it's reportedly $2.99.9. BTW - I'm running a Bank's Six-Gun (full package, monster exhaust, etc.) on position #3 = 60hp plus the Bank's Ram Air intake system. Under extreme conditions of load the turbo's at 24psi and the pyro's at 1325 degrees (the point at which the Bank's equip. defuels it) To test the limits of all the equip., I've charged up some pretty respectable grades at 75mph passing every D & F in sight. Later on the straights, while I'm rolling along at 67mph, here they come around me at 75 - 80mph (with half the trailer/load) just a blowing BLACK smoke. I once told the other truck owner that my truck is governed by the factory at 95mph. They said:
"doesn't that just gripe you? I replied: "not really, because I really don't like to tow over 95mph anyway."
Regards to All
DF

[BMDMAX]

Stock is 1800 RPM. Depending on the tune or module it will move up a bit, typically around 2100, to as high as 2600 for some race tunes.

The LLY and LBZ trucks tend to find peak torque quicker than the LB7 as well due to the VVT and can hold a longer torque curve.

[Melvin P. Thorpe]

I pull a 10,000# trailer over some high mts. here in the west and I have found that 25000 RPM when kicked out of overdrive gives me 62MPH on cruise control and low temp's. I can pull anything mountain out here at that RPM and still keep temp low. I run an Edge on power level #2, Banks turbo back exhaust and AFE intake. Unless the run is very long and high like out of Salt Lake or over the grapevine I never have to kick it out of OD to keep temps low. As my RPM drops below 2000 when pulling a grade w/loaded trailer my temps rise so I kick it down. The newer D/A's have a button but us old LB7 guys have to kick it down. BTW, cruise control on the D/A is great. Not scientific, just my observations.

[More Power]

The LB7 & LLY peak at 1800, and the LBZ peaks at 1600. However, the Duramax has a relatively flat torque curve, which broadens the range of efficiency. Wind resistance is perhaps a more important factor, as is mentioned by others here in this thread. Keep your speed at/below 65 if you're driving for fuel economy. 55 would be even better, but can anyone drive that slow? ;)

Jim

[REDTRUCK05]

I just returned from WY towing a 15k (approx. 22.5k including my 2004 GMC K3500 CC 4X4 LB) 36ft 5'er, about 628 miles. Mileage varied from 11mpg in the tough stuff to 13.4 clear sailing. I make decent time traveling at 67mph and 2000 rpm will pull respectable hills without shifting out of OD. I just turned 50k on my truck and tow about 15-20% of the time. I used to tow at 72mph, but I'd rather have the increase in economy, than get there a little sooner. My trip through the Pacific NW in July/Aug, (2,700 miles) diesel was as high as $3.69.9! Yesterday, I paid $3.09.9 in St. George,UT and back in Vegas, it's reportedly $2.99.9. BTW - I'm running a Bank's Six-Gun (full package, monster exhaust, etc.) on position #3 = 60hp plus the Bank's Ram Air intake system. Under extreme conditions of load the turbo's at 24psi and the pyro's at 1325 degrees (the point at which the Bank's equip. defuels it) To test the limits of all the equip., I've charged up some pretty respectable grades at 75mph passing every D & F in sight. Later on the straights, while I'm rolling along at 67mph, here they come around me at 75 - 80mph (with half the trailer/load) just a blowing BLACK smoke. I once told the other truck owner that my truck is governed by the factory at 95mph. They said:
"doesn't that just gripe you? I replied: "not really, because I really don't like to tow over 95mph anyway."
Regards to All
DF
Does any of your mods cause a problem with your dealer? Void warranty?

[Freeman777]

RedTruck05:
Sorry for the delay in getting back to you. I posted that mess. almost two weeks ago and just now thought to check it. Just before I turned 36k I took my truck in to the dealer, because I had an annoying surging problem at idle. I knew they would take one look at the Banks brain-box under the hood and attribute my problems to the modification. So I went to camping world (in Henderson, NV) and had their best Banks man remove the brain-box which I sent back to Banks HQ for a review of the hard-drive. Gm said I had a bad injector (it was remaining open) and they replaced same. Banks returned my B-box with the latest up-grades. Took it back to Camping World where an inexperienced (the tech I wanted was busy. I should have insisted on him) tech. put it back in and screwed it up. It wouldn't start. Other tech had to drop was he was doing and got it started by disconnecting and then re-connecting the batteries to establish a better ground.) Later on It started throwing codes (Check engine light would come on periodically, threw codes pertaining to: check transmission and drive line, glow plug light would not go out until I started the engine) Took it to Gm to have the codes analyzed and guest what? They said it was the Banks system making it throw (false?) codes. Took it back to Banks HQ in Azusa, CA and they wired in a new brain box in an effort to correct the problem. Got back home to Vegas and it started throwing codes, but apparently they are false codes as there are no symptoms of any problems. It's getting better, very seldom does it light the engine code and then it usually goes out some where down the road.