I'm new to this site & haven't posted before so forgive my ignorance if I'm posting in the wrong place. I've run stock Dodge diesels for years in my business with great success. My personal 2005 3500 single rear wheel, 6 speed manual trans, is averaging 21.4 MPG. It's completely stock except cat & muffler removed, running straight pipe. I'm convinced it could get better mileage if I could slow the rpm at highway speeds. At 70 mph it's turning 2000 rpm with a 3.73 ratio. Anyone have any experience with changing the ratio or adding an overdirve?

 

2000-2100 rpm is right where you want to be for mpgs. That's my best rpm for mpg anyway.

Bigger tires would drop you down some in rpm, but whatever mpg gains you'd get on the highway you'll lose accelerating between stoplights in town.

 

Gear Vendors have an add-on overdrive but it comes at a price $$$

 

The search engine on this site would reveal that this subject has been discussed at length. There are overdrive units and numerically lower gears available, as well as the idea of using taller tires. You might want to read a little of the available information and then see if you have any additional questions.

 

From what I've seen from running in 5th in heavy traffic, and from having had a truck with a NV5600 and a truck with a G56 with a lower OD, RPM doesn't seem to make much of a difference in MPG.

Road speed, however, makes a HUGE difference.

If you usually run 70+ I'd bet dropping to 65 would make a much, much greater change, and it would be free.


Anyway, welcome to the forums.

 

I agree 100% with that. Speed will cut your mileage down faster than almost anything else.