ShinerBock wrote:
4x4ord wrote:
What mileage do you get in 5th vs 6th towing your 13 k trailer?
:S
I don't know why your truck's fuel economy is such a secret but anyway here's a map giving you all the benefit I can give you. The yellow and red dots represent 8 mpg.
According to your data a 6.7 Cummins pulling about as hard as it possibly can in 5th puts it at 832 Nm of torque output at 65 mph and 1375 rpm. The red dot is at the exact same power output. This power output represents 8mpg at 65 mph. Notice that according to the graph both gears are getting similar fuel economy with a slight favour possibly going to 5th gear.
As the hills get steeper 6th does not offer enough torque and the transmission absolutely has to shift to 5th so the green line represents shared output during heavier parts of the pull.
As the load gets lighter the bottom of the yellow line corresponds to the same power output as the bottom of the red line... Notice how the 6th gear is clearly getting better fuel economy during these stages of the journey.
There is absolutely no way that this BSFC map supports any claim that 5th gear will produce better fuel economy towing a 13k trailer than 6th gear.
Even if you slow down and increase the load by going up a steeper incline so that 5th gear is in the dark blue sweet spot a corresponding power output @ the same mph for 6th gear does not exist on the BSFC map. IE under heavy loads the transmission absolutely must downshift for the truck to maintain speed.
