F450 vs Ram 3500 DRW tow vehicle

4x4ord wrote:

ShinerBock wrote:

4x4ord wrote:
^^^^ The thing is pulling an 18000 lb rv down the highway at 70 mph is light work. At 2000 rpm the 2020 Powerstroke can make approximately 380 HP. Even if you have an RV that requires 180 HP to tow it down the highway at 70 mph, why would you want your truck geared such that the engine revs to an rpm where it is able to produce over double the required HP? 4.30 gears are too deep for us RVers, especially when they are offering us a 10 speed transmission. If you have a 10 speed transmission and 3.55 gears and find yourself towing against a wind or in light hills and find the transmission is dropping out of 10th too often for your liking, you can simply lock out 10th gear.

The 10th gear in the 10R140 is the same as 6th in my 68RFE. I also have 3.42 gears. I get better fuel mileage if I put mine in 5th(which is about 8th in the 10R140) towing my 14k trailer. I used to tow it in 6th down to the same 160 mile route to the coast(which is mostly flat) the first few years I had the truck. About three years ago I started towing it in 5th, and my app calculated numbers fuel mileage shows that I averaged better fuel mile towing in 5th than I do 6th.

My truck can easily tow it in 6th, but I noticed that I had to put the engine under more load than I did in 6th. My fuel rail pressure pressure was much higher on average along with my EGT's and boost in 6th than 5th. Line pressure in my trans is lower to since it is not trying to keep the clutch of such a low gear together. This inturn lower trans temps.

I've never seen a brake specific fuel consumption graph that supports what you're claiming on a stock engine. Gearing up and throttling down saves fuel under light load conditions. I wonder if your aftermarket program is over fueling at low rpm and high throttle position to produce high torque at the expense of engine efficiency?

My truck was tuned withing 30k miles and towed with it for at least one year before I switched to towing in 5th. My brother also has a 2014 just like I do that was 100% as of a few weeks ago and saw the same results I did. Cummins power spec states that the 6.7L is most effeicnt between 1,800 and 2,000 rpms when towing. That is what what Cummins tuned/design the cam/turbo and rest of the engine for. Can't speak for the Powerstroke though since every engine is tuned/designed differently.

I remember Cummins used to publish this kind of data below, but I haven't seen one of these charts below(for the 5.9L) in a long time. I will try to find one for the 6.7L. I would wager it would show some similar as below.