What is the Optimal engine RPM for mileage? I am trying to decide what gear/tranny combo is best for behind a 6.2 for mileage without sacrificing performance as well... Any suggestions?

About 1800 rpm will yield the best flat ground cruising mileage.

How about 2000? Looks like with a 700R4 and 4:10's 65MPH is 2000 RPM, with 31" tires. (better than a TH400 with 3:08)


http://www.dfw-tx4wd.org/gears.html is a wonderful site for figuring things.

Heres what it boils down to. the M1009 I am looking at uses a TH400 with 3:08. My old 'trusty rusty' has 4:10's and I have a TH700R4 available to use. Trying to decide which combo is best....

1. Leave it alone with TH400 and 3:08 (2300 RPM at 65mph with 31")

2. Put 700R4 in it with 3:08 (1500 RPM at 65mph with 31")

3. Put 700R4 and 4:10's in it. (2000 RPM at 65mph with 31")

My guess is for best throttle response choice #3 is the best. I also know that choice 2 can be a little doggy with a 6.2 (my bro had that setup in a blazer).

Whats everyone think?

The 700R4 will give you the best off the line take-off, and the OD will give you the best mileage, I say stick with that and the 4.10s. 2000 is about right, maybe a touch slow for a 6.2, but it should be able to hold highway speed no prob.

Certainly would be alot better than the 'factory blazer' type setup of the R4 and 3:08's I would figure. I like that plan the best anyway as I get to use my 3/4 ton axles then and keep my custom rear disc brakes too... :cool2:

What do you want, power or mileage? Ideal combination would be 700r4 and 4.10, used to give me consistant 20 mpg in 83 3/4 ton truck and sub. On the other hand, 700r4 and 3.08 and 29 inch tires have yielded close to 30 mpg(also very poor transmission life and downshift at every gopher mound.):h

so basically the 700r4 and 3:08 combo is a horrible idea. No reason to trash trannys and always have to downshift at gopher mounds. It seems that what I will probably do is drive it for a bit with the th400 and 3:08's for a bit, while I rebuild the ball joints and such on the 4:10 axles and the 700r4 tranny. Where can I get a good rebuild kit for the 'r4'? I have done a th400 myself, and am sure I can do the other. Also is the torque converter the same between them?

No, the 700R4 has a different convertor. The lockup clutch, size of the snout, stall speed, pump drive dogs, etc. Just completely different. Be sure to upgrade to an H.D. convertor if you do put the 700 in. Trans modifications would help as well. Any reputable trans rebuild shop can supply upgraded parts.