6.4 litre HEMI vs Cummins
Hi all Just upgrade TV from a Dodge 2500 6.4 litre to a 2500 Cummins Looking to see if anyone else made this change to share your experiences on gas mileage. Did the cummins make a difference in...
Forum Discussion
Me Again wrote:ShinerBock wrote:
The Cummins gets horrible gas mileage.... It does get good diesel mileage though... ;)
Expect about 15-16 mpg(calculated) combined depending on how you drive and terrain. The computer may say 17-18, but it lies.
Also, when you tow over 5k, lock out 6th at speeds under 73 mph for best fuel mileage if you have a 3.42 rear end.
I have been towing the 8k TT in 6th without TH and getting better mileage. In 5th the 16K 5th and 8K TT got similar mileage.
It is speed and load depended. As you can see the BSFC map below. The "sweet spot" for the Cummins 6.7L under load is between 1,600 and 1,900 rpm. The red dots/lines is 6th gear and the four vertical lines staring from the left is my rpms at 60, 65, 70, and 75 mph while what I tow. The yellow dots/lines is my rpms in 5th at the same speeds. The horizontal lines are grade/load starting with 0% grade at the bottom.
On completely flat ground and no drag, 6th is generally best, but even a slight 1% grade and moderate drag will put enough load on the engine to make 5th the better choice which is why I generally leave it in 5th and forget it unless I am going past 72-74 mph.
