2011 Detroit dd15 owners What would be good hp for fuel mileage

Your ratings are very good. Your 7mpg is very good. We had a 500 detroit with a 1550 torque shaft that did 11 mpg once downhill eastbound in Kansas with the wind at our back on 70 for a while.

My opinion is this. Hold on to your ratings and keep them. Do not bump them for two reasons, you might guzzle the precious 20 gallons left while still 120 miles from that lonely refueling spot in some Bundry Arizona because your engine is a snorter. You might pull your drive shaft at the scales trying to slide tandems if that shaft is not rated to accept 1800 pounds torque.

Back in the 80's we had maybe 250 or 290 out of a big cam 4 or a mack perhaps. kitty cat 425's were king at 4 to 5 mpg. Mountain climbing at 45 mph saved you time loaded rather than grinding at 5th low 21 mph for a hour. Adequate torque and horsepower such as you are displaying to me is no problem.

WIth that said, with the right rig at 500-650 horse and 1600 to 2000 pounds torque will create a sitaution where you WILL save fuel by burning less per hour to climb across say... Town Hill in a short time without having to get into the motor too much at almost full highway speed. And when you DO run into that killer 21% grade you will have the beef and guts to run it carefully and steady without burning up anything as I have done once or twice because my 350 cat was inadequate.

 

I have a custom tune on mine, I am running 700hp & 1800lbft of torque.
My 30 day average is sitting at 7.6mpg but my truck does not have SCR & has been cleaned up.

 

I doubt changing your rating will have much effect on mpg.

 

700hp and 1800ftlb? Is that on a dyno or what someone told you? Those numbers do not jive in the least, please explain these numbers.

 

Depends what lane you run. If your in big hills then more power can help you, if you run flat Midwest land I would leave it. Personally I'd set it at a 500/1850

 

I would agree 500/1850 is adequate for most applications that aren't heavy haul or something specialized.

 

Upgraded clutch 2050 lbs .. so did u upgrade it or was it factory fitted..
I believe most detroit transmissions are rated around 1650… so shouldn’t the clutch be of same rating?