93 Hdj81 37" tires and diff gears?

[stvrn6]

I have 35s and 4.88s with my 1hdt. Its geared too low for sure, I have the overdrive transfercase gears I was going to put in, seems like its screaming on the highway.

What RPMS do you see at like 70 mph? I'm assuming your auto too?

 

[TheBussman]

What RPMS do you see at like 70 mph? I'm assuming your auto too?

yes auto, 2500 at 65 mph, more at 70 but i didn't write it down.

 

[Beach80]

So, I should put an update of the route I took. I installed 3.11 low gears and 10% underdrive in my transfer case initially (I was on 35's). Then after going to 37's I re-geared to 4.56. This put me very close to stock rpm's at highway speeds. Im very happy with it. There are some advantages to doing it this way but it is more expensive than if I had just done 4.88 gears.

 

[Beach80]

What RPMS do you see at like 70 mph? I'm assuming your auto too?

This may help you on your rpm questions. My calculated rpm's for having 10%underdrive and 4.56 gears and my actual rpm's all matched up very close.

 

[bug616]

Really old thread but just curious, what were your usual highway speeds and RPM? Did you ever calculate your mpg? I have newly rebuilt 4.88s I was considering throwing under my HDJ81 but I fear 35s may be too small. Might be time to jump to 37s.

At 70mph on GPS my RPM is 2600. I average 16 mpg when not towing or 13mpg towing.

 

[Haulinglass]

Interested in this also. I have a 1hdfte that I’m considering doing 37s

 

[Beach80]

Interested in this also. I have a 1hdfte that I’m considering doing 37s

In my earlier post, I have the calculated values for my rig. Do the same thing for your rig and it will answer your question of what setup fits you best.

 

[Haulinglass]

Thanks I must have scrolled right past it.