gears or engine upgrade?

'96, np231, 30" tires, auto, 3.55 gears

I've noticed a bit of a difference in power in my Xj since going to 30" tires. I may go to 31's in the future, but I really don't see me doing much more than that... More into trail riding than the real gnarly stuff.

anyhoo, I'd like to regain the power I've lost, as well as a little more. I don't know if it is worth my while to regear. gears and labour are costly.

I'm planning an engine rebuild next year, and was wondering about simply porting the heads, freeing up the intake, install a free flow exhaust, and installing an RV cam. I figure if I can make the engine perform well at a lower RPM, and have it making more power than stock, I'll probably get the performance I want and better gas mileage than what I would by swapping to 4.10 gears.

The other factor in this is the DIY factor. I am an apprentice mechanic. I am not comfortable setting up gears, but have rebuilt several engines with good results, and have the necesary tools for a rebuild.

Ideas and input?

Thanks,
Geoff

Gears aren't necessary for 31's. Do the bolt-ons and p+p the head and you'll be ahead of the game. Good luck.

While building the engine for more power/torque may feel like it's doing a better job of overcoming the loss of power it will do little to fight the stress you are putting on the transmission, etc. in the form of heat.

Regearing will increase the mechanical advantage the engine/transmission/t-case have on the tires. A great deal of stress is added to these components when they are required to do more work to turn the larger tires. By adding numerically higher gearing you are decreasing the amount of work the engine has to do to turn the tires and also decreasing the amount of work the transmission has to transmit to the rear tires.

HTH.

Hmmm.... never stopped to consider what this is doing to the auto trans. Something to consider. BUT...

How much strain do larger tires put on an auto trans? Our XJ's come with a pretty good tow rating. I can't imagine the auto trans suffering any more from running 30's or 31's than it would from pulling a trailer even half the rated tow rating of 5200lbs.

Geoff

one word: tranny cooler well thats two, but you get the idea. I have a comanche on 31s and it goes fine when the motor is running good. I wouldnt mess wit the gears unless you go 32s or higher.

I regeared to 4.10s with 30s and love it. Crawls nice and slow, and tows extremely well. Worth it to me.

Fergie

Back when I first bought my truck, it was 2wd stick with 3.08 gears and came with some little Perelli tires on it. I soon went to 30" BFGs and the thing suddenly felt like a slug. I wasn't about to give up my new shoes, so I dealt with it and upgraded the ignition, intake, exhaust and other various power add-ons (but nothing internal). Then the Dana 35 blew up on me and I sought out a Dana 44 with 3.55 gears (an upgrade to sticks with the 3.08s). It was the BEST thing I'd done to the truck yet!! The truck came alive! It launched off the line and I could make it up the Rouge River bridge (freeway speeds) in 5th again. In my opinion, the absolute BEST thing that anyone can do to their Jeep is gears! Save up and go for 4.10s, I promise that you'll be smiling despite the pain in your wallet.
Oh, and junkyard axles can be a cheaper way to go, but since yours are 96, you gotta be careful not to get crappier axle just to save a few bucks on gears. If you do get gears, now's the time to think about selectable lockers. If you REALLY want to smile offroad, a rear selectable is the ticket.
Jeep on!
--Pete


ComancheClub.com

My '88 MJ still had stock 3.08 gears when I bought it, although it was lifted and the wheel wells had been hacked out for what must have been some fairly big tires, cause 31s didn't begin to fill them out. On 31s it was a dog. I had boiught a set of 3.73s to use in my XJ with 30" tires, so I tossed them into the MJ.

With 31s, the 3.73 gears provide the same exact final drive ratio (RPMs to MPH) as stock tires and 3.54 gears. The XJ is a little "doggy" running 30" tires and 3.08 gears, but not horrible. With an automatic, I really don't think regearing is necessary for street and mild off-road. If you intend to do the engine anyway, I think the option of a little porting and polishing and a good torquer camshaft would be the way to go.

You didn't say what axle you had in the rear... If it was me and I has the D35 I owuld go find a suitable 4cyl xj in the j-yard to grab the axles out of and get the 4.10's that you wanted. As a matter of a fact that is what I did for my project Mj in the garage now. It has the 4.0, the ax15 and the 3.08's. This swap is cheaper, parts wise and time wise for me, then going to buy gears, and pay a mech/buy tools to do the job.



Patrick

cj7xjmj said:

You didn't say what axle you had in the rear... If it was me and I has the D35 I owuld go find a suitable 4cyl xj in the j-yard to grab the axles out of and get the 4.10's that you wanted. As a matter of a fact that is what I did for my project Mj in the garage now. It has the 4.0, the ax15 and the 3.08's. This swap is cheaper, parts wise and time wise for me, then going to buy gears, and pay a mech/buy tools to do the job.

Patrick

Click to expand...

1)I hear a lot about grabbing an axle from the junkyard when people talk about regearing. Probably a stupid question but why is this?

2)Is the idea that you can rebuild the used one while your XJ is still driveable or did the 4 cylinders come with 4.10's?

3)If they did come with the 4.10's is this the same axle as the 6 cyl. just with different gears?

Sorry if I'm hijacking, just a little confused...

In the early years 4-cyl XJs could have come with 3.54s, 3.73s, 4.10s or even an occasional 3.31. Chrysler cut that down to just using 4.10s behind all the 4-cylinders. So buying a complete axle for $75 to $150 is a lot cheaper than paying twice that for gears and bearings, and then paying as much or more on top of that to have the new gears installed and set up.

Eagle said:

In the early years 4-cyl XJs could have come with 3.54s, 3.73s, 4.10s or even an occasional 3.31. Chrysler cut that down to just using 4.10s behind all the 4-cylinders. So buying a complete axle for $75 to $150 is a lot cheaper than paying twice that for gears and bearings, and then paying as much or more on top of that to have the new gears installed and set up.

Click to expand...

Is it possible to find the 8.25 with these gears? Is it a completely bolt on swap?

Can you do it with the front axle as well?

Thanks

ecrogers said:

Is it possible to find the 8.25 with these gears? Is it a completely bolt on swap?

Can you do it with the front axle as well?

Thanks

Click to expand...

yes, yes, yes

the rear 8.25 from a 96+ would be better because the stronger axle shafts. Chry is a complete bolt on swap from a d35...
the front from a pre 97? and post 91 would be high pinion reverse rotation and non-disco, i remember hearing that the 97+ were LP like the TJ

XJ_ranger said:

the front from a pre 97? and post 91 would be high pinion reverse rotation and non-disco, i remember hearing that the 97+ were LP like the TJ

Click to expand...

You heard wrong. The XJ stayed with a high pinion front axle through 1999. The low pinion came with the 2000 model year.

Well tell me this. Did 8.25 29spline ever come behind the later 4cyl with 4.10's?

scoobyxj said:

Well tell me this. Did 8.25 29spline ever come behind the later 4cyl with 4.10's?

Click to expand...

interested to know the answer as well
according to the search terms on www.car-pat.com that alxe does exist...
hth
-Ranger

scoobyxj said:

Well tell me this. Did 8.25 29spline ever come behind the later 4cyl with 4.10's?

Click to expand...

Does anyone know if you can find one of these?