BTW, I am assuming that gas mileage on the highway goes down the tubes when you do these gear mods????

After I installed my 5.29 gears (running 33x12.5's) I've observed that I'm getting about 16-17 MPG on the highway with my 2.6, but I haven't even attempted to drive conservatively.....am constantly gassing it without concern for economy and am usually pushing my "barn door" at 75 MPH+ on the highway.

After installing new t-case gears I noticed a huge change in crawl right away.

If you want the biggest bang for the buck for the trail first, then get the t-case gears first. If you want the biggest bang for the buck for the highway first, then get the diff gears first. Consider that the t-case gears only involve just them and the t-case, however, if you want to do the diff gears AND the front locker, you will be better-off doing them at the same time, so you'd best have all the components in hand when you do it.

I got the t-case gears installed first.

Here is an example of my concern:

I have 4.272 gears in my diffs right now. Changing nothing else, if I upgrade to 4.90 gears in my diffs, my gas mileage has to decrease since my engine will have to do more RPM's to maintain the same speed on the highway that it used to with the 4.272 gears. Can anyone verify this theory??

What size were the original stock tires on your rig? I wouldn't know for sure, but I'd think they were smaller than 32's.

EDIT: Yes, your engine would have to spin more RPM, but it should work less doing it. It will likely affect your mileage, but are you up-sizing your tires?

It's a definite maybe. Too many factors. If youÆd have very powerful engine than it would prob be true. On somewhat less powerful, at least considering power/weight ratio, it would depend on other circumstances like driving up the hill, speed, larger tires etc. It could quite possibly be easier on the engine (meaning less throttle), to drive with lower gears then higher leading in some cases to possibly better mileage. Unfortunately this kind of swap will prob co-inside with larger tires, lifts and other nice perks of 4wheeling rig. Those will have much greater deteriorating effect on mpg then higher engine RPMs by itself. We are only talking about 15% change in gear ratio, and correspondinly RPM. I wouldn't expect that to have significant effect by itself.

Well, on the 97 SR, I will without a doubt do both t case gears and diff gears. My question was mainly for my 97 LS that has the tow bar on it. I was thinking not to use the SR for towing a trailer b/c I wanted to set it up for wheeling only, so I wasn't going to put a receiver on my custom rear bumper design for the SR. My LS already has the tow package put on it (I did it long ago) so if I eventually get a trailer to tow quads and stuff like that, I was planning to use the LS. At most, it would have 32's on it and it has the 4.272 gears in it. I already towed a total of 10,000 lbs (vehicle plus trailer) accross the country with my LS when I moved out here and it had 32's on it. It did ok, but definately needed 3rd gear to go up hills on a highway and couldn't really keep up with traffic. I am starting to think that it might benefit me to put 4.90's in my LS for towing purposes, but was wondering if it would kill my regular driving gas mileage when I didn't have any weight in it. I suppose in time, maybe I will get the 4.90 gears for both my LS and SR. Opinions?

I'd say go ahead particularly if you have larger tires (stock LS was something like 235/75R16 I believe). Just take a look at Gen 3. The gear ratio for XLS was 4.9 while Limited has 4.3 . They are rated 14/17 and 13/18 correspondingly for 2001 and 15/19 & 14/19 for 2002 <img src="/forums/images/graemlins/confused.gif" alt="" />

I can't comment on the Mitsubishi Montero/Sports but in the Jeep world, for example:

ZJ/WJ Grand Cherokee
3.73 Stock Gearing with 29" Tires

4.11 is stock with about a 30.5" tire
4.56 would be stock like gearing with a 31"~32" tire.
(I have real world as I ran 31" tires on my old ZJ with 4.56 gears)


This translates the same to any vehicle.

The distance traveled (1 revolution) of the tire increases and so your rpm's are actually decreased for a higher rate of speed.

When the tire size increases, to increase the rpm's back up to the "sweet spot" you have to change your gear ratios as well to a lower gear ratio (numerically higher.)


2001 3.0L montero sport U.S. version has 4.90 gears stock.

OK, have another question:

Did Mitsubishi make 4.88 diff gears and 4.90 diff gears or are they the same thing? I came accross a pair (front and rear) of mitsu diffs that I have been told have 4.88 gears in them. Are these the same thing as the 4.90 gears and will they fit into my 97 SR?

the 4.875 diffs are NOT the same as thr 4.90 diffs.

The 4.90 diffs are way much bigger 12bolt v 10 bolt. They are not interchangeable.

If your vehicle has the 3.5l motor then it should have the larger diffs. In Aust the standard ratio was 4.636 , the 4.90 diffs you speak of were fitted to diesel vehicles in Aust.

When I had my 97 NK 3.5lDOHC I swapped in 4.90 gears but found it generally a waste of $$$$.

However if you guys are going from 4.30 diffs to 4.90 then IMO that is a more marked improvement.

cheers