ShinerBock wrote:
4x4ord wrote:
ShinerBock wrote:
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.
If the Ram/Cummins engineers believed they could increase the fuel economy of their trucks by holding the truck in a lower gear at 60 mph to keep the engine at 1800 rpm instead of shifting into overdrive do you honestly think they wouldn't do it? Try it on your Ram .... drive at 1800 rpm in 4th gear and measure your fuel economy and mph. Now drive the exact same test in drive (presumably 6th gear)at the same mph ... there is no way you are going to measure better fuel economy at 1800 rpm and 4th than what you will measure in the gear the truck wants to run in.
I have! I have driven the same 160 mile route to the cost towing my 5ver in 6th and in 5th many times. Filled up before and after to get calculated numbers instead of computer. Averaging out each time I towed in 6th and in 5th on my app, I got better fuel mileage in 5th. Unloaded or very light loads below 5k or 7k with low drag, being at the lowest rpm possible is best for fuel economy according to my calculated numbers.
My truck does not know whether I am towing 6k or 12k to know which gear is the best one to stay in. All it knows is pressure, load(throttle input), and rpm to dictate which gear to be in. It is like fuel tables. If it sees X pressure, Y load, and Z rpm, then it looks up this point on the table to see if it should up shift or or not. It knows nothing about the trailer you are towing or if you are about to come up on an incline to downshift. It is not that smart.
Unless the Ram/Cummins engineers are idiots which I am certain they are not your transmission will do better at selecting the appropriate gear for fuel economy than you can. I just did a quick search to see what Cummins says about running the 6.7 at 1800 rpm:
Here
