Finally got my Diesel!

[HillBilly2]

I just got a 90 4x4 1500 burb with a bad tranny. Got a new 700R Level3 from Bowtie Overdrive with a 1600 rpm convertor on the way. Hope to have it on the road in another week or two.

I'm looking for maximum mileage. 90% of my driving will be interstate at 70-75 mph. Doubt if I will ever tow anything. From the calculations I've seen, I should probably run 3.42's with 32" tires. I have 3.73's now.

I could change the gears, or get used axles in the right ratio. If I get used axles, should I get 2500 axles (stronger) for more durability? I can find either for about the same price. Do not want to change springs, no need to make the ride any rougher if I'm not going to be hauling a lot of weight. Good idea? Bad idea? How about driveshafts? I would not mind ending up with a bulletproof suspension, and still get 24-25 mpg highway.

What do you think?

[moondoggie]

Good Day!

If your Sub has 235/75R15 rubber, @ 70 mph:

gears rpm
3.73 2188
3.42 2006
3.08 1807

I've heard that 1800 rpm is the sweet spot for mpg, so 3.08's might be best for what you want to do. That's what's in my 82, & it gave fantastic mpg.

Keep in mind: If you spend $500, & this truck presently gets 20 mpg, & you figure it'll get 21 mpg with the gear change, & fuel is $2.60 per gallon, it'll take you ~ 81K miles to pay for the gear change.

I'm also a little pessimistic about how much mpg might be gained, unless you go all the way to 3.08's. In my 95, I went from 8% oversize tires & normal gears, to 4% oversize tires & a Gear Vendor Aux. OD. So, my effective ratio on the highway went from 3.80 to 3.08; I gained maybe 2 mpg.

Also, any taller gears & you'll be able to describe acceleration as "perceptible."

Blessings!

[More Power]

The 3.73's could be a better choice if you intend to drive 70-75. An NA 6.2 above 65-mph needs more rpm to achieve the power required to overcome the effects of increasing aerodynamic drag. Adding a turbo would change the diff gearing recommendation... :)

My 31x10.50R15 tire, 3.42 geared & 700R4 equipped 6.2L GMC K1500 with a Banks turbocharger produced 22-24 mpg at 65, and 17-mpg at 85-mph (there was a brief time here in MT during the mid 90's when there was no speed limit on the Interstate).

Jim