370 ratio

i think the way it works out is like this: the lower the number, the better the mpg. the engine has to turn the driveshaft 3.7 times to turn the wheels once, so lower is better - 3 turns is more efficient than 4 turns to spin the drive wheel once. on the flipside of the coin, if all you do it pull up mountains, a high ratio is better cause it will give you more torque to maintain a decent uphill speed, and your mpg is gonna suck anyway, since you are going uphill for an extended period of time.

someone correct me if i am wrong.

 

It all depends on the ideal rpm range of the engine. There is nothing wrong with a 3.70 joined with the right engine, tire size, road speed, etc. And there are other factors. A 10 speed direct drive tied to 2.64 rears is more efficient than a 10 speed OD tied to 3.55's. Though both are turning the same RPM at the same speed in 10th. The senior engineer at Eaton verbally confirmed this at the 2011 MATS, and claimed a 3-4% better efficiency. And the 10 speed direct tied to 2.64 compared to a 10 speed OD tied to 3.55 will pull the same hills with no difference in ability to do so.

The only issues with using a 10 speed OD with 3.70 is the best operating rpm of the engine and the speed you choose to run. Running at higher speeds would be better done with taller gears like 3.55 or 3.42 if we are talking only about fuel mileage compared to a 3.70, which seemed to be what you were asking. The 3.70 is just as efficient at the right engine RPM as any other ratio.

 

With a 13 I turn 1500 RPM at 70 mph. If your in the moutains a lot you will like a 3.70. However I would ditch the 10 speed.

 

why would would you ditch the 10 speed

 

I have a 13 double over with a 3:70, 1850torque, and it pulls great through KY,WV,TN etc. I find my best mileage is at 63mph, around 1425rpm. Much better performance upping the torque from 1650 to 1850.

 

Well in those states the speed limit is 70. Thats what I run. May get best fuel mileage at your speed but I get over 5 mpg for the most part. Thats good enough for me.