4x4ord wrote:
Shiner, you are applying a little bit of truth improperly to come up with a stupid recommendation.
I couldn't read your post without at least doing a simple test to give some real somewhat scientific numbers so:
I drove my truck in 5th gear at 1800 rpm/92 kph up a long incline and measured the fuel economy on the DIC .... 13mpg (18.6 liters per 100). I turned around, went back and conducted the same test at 92 km per hour in 6th gear .... 13.6 mpg (17.8 liters per 100). I then did a similar experiment over a stretch of highway going down a grade for the duration of the test... 43 mpg in 6th at 92 kph and 33 mpg in 5th at 1800 rpm/92kph. So although a diesel engine may be most efficient at 1800 rpm it is best to let the engineers worry about what gear and rpm your truck should run at. Put it in "D" and go. And choose the highest speed rear end recommended for the load you expect to tow.
Yeah, you are right and Cummins engineers are wrong. What are they thinking? Also, the algorithms the truck computers uses is not even close to being 100% accurate. It does not measure the actual amount of fuel used and instead relies on various sensors and PID's to come up with it's number.
BTW, I am not making a recommendation here. I am just posting information I have that explains why every diesel BSFC map I have seen shows that it's peak efficiency
under load is around 1,800 rpm.
I am also not sure you know how transmission tuning works. It is a vanilla tuning that relies on pressure, rpms, and throttle input to know when to shift. It does not have the AI capabilities to know what kind of load you are carrying, the drag resistance, the weight, or if you are about to come up to a hill so it will know to downshift. The only transmissions that I know can do that are the Eaton Endurant transmissions which they(Eaton) teamed up with Cummins to program the transmission to shift according to GPS data and grade sensors inside the trans. This GPS data is constantly being updated. You are giving your truck's TCM more credit than it is due. It is not that smart.
