ShinerBock wrote:4x4ord wrote:
I would guess that towing 13k down the highway at 65 mph takes about 140 hp. If an engine is designed to put out 300 hp at 1700 rpm and 400 hp at 2800 I’m thinking it is lightly loaded towing a 13k trailer. The best rpm to tow at for fuel economy is not mystical. If a transmission control module is loaded with a BSFC map it is very easy for it to “know” exactly and instantaneously where it is on the map at all times. The decision to shift or not should be very simple for a computer ..... “I’m at 600 Nm at 1270 rpm and after the shift I’ll be at 1700 rpm and 450 Nm. My BSFC is better after the shift hmmm I think I’ll shift.” We have only a seat of the pants feel for where our trucks are running in relation to their BSFC map ..... especially when we have never even seen a map for our engine.
1) Your 140 hp assumption is based on flat land and normal wind drag. I have told you multiple times that my route to the cost is not flat and the part that is flat has very high wind(next to a wind farm). The terrain is a constant up down with up to 3% grades. I am not sure why you keep neglecting this part. My truck will pull most hills in 6th, but I have to put my foot more to the floor to do so. 5th requires considerably less throttle.
Your truck has been tuned so it could be that even though it can make big torque at low rpm it might not get enough air to do it efficiently... I don't know. We agree that a stock Cummins 6.7 towing up a 3% grade should be in 5th. If conditions are such that the transmission is constantly and annoyingly shifting back and forth, lock out 6th. We agree on that as well. I'm pretty sure my Ford will downshift if it's pulling hard enough to be down at 8 mpg and 1400 rpm but when the road levels out it will upshift back to 6th .... it's an automatic.
2)Transmission control is not loaded with a BSFC maps. It is multiple charts that basically says at X rpm, Y load, and Z throttle position upshift or downshift(there are a few other parameters depending on the make). The way you think it works and the way it actually works are two different things my friend. All it knows is to shift when the preset parameters are met. If it was able to be tuned like you think it is, then there would be no need for tow/haul mode or select shift.
I tell you what, why don't you contact Ram and tell them your brilliant idea and how they should be tuning their transmissions from now on. Let us know what they tell you.
