97 XJ Engine Swap Choice?

notice so much out there, was wanting some professional opinions (been out of the game for a while)
I still have my 97 Cherokee 4.0l automatic, 3 inch susp lift, running 31's. (arb bumper winch snorkel, rack etc..)


Right now I max out going around 75 mph on the interstate and really struggle in the mountains. Been reading a lot on ls1 engine swaps.


Is it possible to do a engine/transmission swap that would let me sustain 20mpg on the interstate/highway roughly, with having plenty of room to get it up to 90/100 mph. This is a project me and my dad had back in the early 2000's and I would like to put some more money in it and get it up to standards and ready to last another 20 years. Thanks so much!

Umm it's an XJ, mpg and top speed aren't really the strong suit.Probably not going to be getting up to 100 in a XJ. Things are as aerodynamic as a brick. If you want prius mpg and corvette speed. You're talking some decent coin But there's a better option that doesnt require selling your first born...what gears you running? Stock? Regearing will help tremendously. 31s and aw4 4.10 s are nice. If you want to go bigger on tires you'll need deeper gears. Checkout the grimmjeeper gear calculator.

smokeyyank said:

Umm it's an XJ, mpg and top speed aren't really the strong suit.Probably not going to be getting up to 100 in a XJ. Things are as aerodynamic as a brick. If you want prius mpg and corvette speed. You're talking some decent coin But there's a better option that doesnt require selling your first born...what gears you running? Stock? Regearing will help tremendously. 31s and aw4 4.10 s are nice. If you want to go bigger on tires you'll need deeper gears. Checkout the grimmjeeper gear calculator.

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Thanks so much for the reply!
I am running stock gears currently, I dont mind sinking a bit of money into it (lot of sentimental value) and my daily driver is good to go for a while. The engine has around 140k on it currently and I did a lot of "mudding" in it growing up. (flooded it out 2x with water up past the gear shifter) Thankfully the only thing I have had to replace is the waterpump over the years. Do you think regearing with what I have now could get it a bit more top end? (not trying to stress the stock engine out I basically have to floor it going up steaper hills to keep it above 60 mph where i live in the mountains.)
I will research what you recommended, thanks so much for a starting place for me, trying to get it as close to top shape and have it last as long as possible without sinking more then 10 to 15k into it.

I’d second doing gears first

Regearing is not going to get you more top end -- it will let you get up to speed faster although that top speed may actually be a little slower -- your RPMs will be higher with deeper gears at 70 than they currently are now

Higher RPM at speed also means your burning more fuel at highway speeds -- you will use less fuel getting up to speed and around town driving because the motor isn't working as hard to get you moving

A quick second on speed. I don't know about y'all, but my unlifted XJ starts to float at around 95. Only comfortable driving it to 90.

as someone who's done an engine swap on an xj.. it's not all that easy, if you do anything other than spend top $$ on all your components you're going to have continuous problems (cooling in particular), and while it's nice, there are easier ways to get the power (stroker)

that said-- by far the easiest swap these days is an ls. Check out Novack's web site, they make just about everything you need to do a ls/700r4 swap keeping the stock transfer case (which depending on what you have may not be that bad). I wend from my stock i6 to a brand new chevy zz6 400hp/400tq motor, and (obviously) power and acceleration are off the charts. but surprisingly (or maybe not) MPG with 4.11 gears and 700r4 with stock gears (for a 1990 tranny out of a kc10) is more or less what I got with the i6, around 15-20 depending.

But again... expect a fairly difficult swap. these are not easy as compared to, say, the wrangler crowd (using wrangler to apply to the jk/yj/tj etc crowd)

edit-- ++ on the speed. Even with the ability to go far faster, I won't take my truck over 75. half that if I'm taking a turn.

b2Squared said:

Thanks so much for the reply!
I am running stock gears currently, I dont mind sinking a bit of money into it (lot of sentimental value) and my daily driver is good to go for a while. The engine has around 140k on it currently and I did a lot of "mudding" in it growing up. (flooded it out 2x with water up past the gear shifter) Thankfully the only thing I have had to replace is the waterpump over the years. Do you think regearing with what I have now could get it a bit more top end? (not trying to stress the stock engine out I basically have to floor it going up steaper hills to keep it above 60 mph where i live in the mountains.)
I will research what you recommended, thanks so much for a starting place for me, trying to get it as close to top shape and have it last as long as possible without sinking more then 10 to 15k into it.

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No worries, :: is an awesome place full of tons of Jeep nerds. All the info suggested so far is good. If you want to stay with 10-15k I wouldn't swap engine or do anything wild. Regearing will do wonders. What heavyopp suggested is pot on. If you want some more umph after getting gears a stoker would be a great option.

Check out Cal's build on here. Amazing attention to detail and really great documentation on a lot of stuff, especially his stoker build.

https://www.naxja.org/forum/showthread.php?t=1131459

https://www.naxja.org/forum/showthread.php?t=1152254

I just went to 4.56 on 32s and it’s fine at speed on the highway. At 3.55 it wouldn’t stay in overdrive with a headwind. Beats swapping an engine

smokeyyank said:

Umm it's an XJ, mpg and top speed aren't really the strong suit.Probably not going to be getting up to 100 in a XJ.

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That is such an ignorant answer. XJs have a factory speed limiter around 116mph - because they can go that fast and more under their own power. Maybe not safe, but they have the capability and the horsepower. I've had mine up to 120 - not for very long, not very safe, but that's where the speed limiter hit. It certainly has the power and aerodynamics are not a problem. Police model XJs had the speed limiter removed and a calibrated speedo up to 120. No engine modifications.

If your engine is INCAPABLE of doing more than 75 or going up mountains something is wrong. Probably effecting gas mileage too. Adding a small lift and 31s will make it more sluggish off the line, but once up to speed you should not have a problem. Gears will help for sure...but if you can't go past 75 now, that is not what is stopping you.

I drive mine all day on the freeway at 80-85 - because that's what the posted limit is and the speed traffic is moving at. I have smaller tires but 31s aren't that huge.

Number21 said:

That is such an ignorant answer. XJs have a factory speed limiter around 116mph - because they can go that fast and more under their own power. Maybe not safe, but they have the capability and the horsepower. I've had mine up to 120 - not for very long, not very safe, but that's where the speed limiter hit. It certainly has the power and aerodynamics are not a problem. Police model XJs had the speed limiter removed and a calibrated speedo up to 120. No engine modifications.

If your engine is INCAPABLE of doing more than 75 or going up mountains something is wrong. Probably effecting gas mileage too. Adding a small lift and 31s will make it more sluggish off the line, but once up to speed you should not have a problem. Gears will help for sure...but if you can't go past 75 now, that is not what is stopping you.

I drive mine all day on the freeway at 80-85 - because that's what the posted limit is and the speed traffic is moving at. I have smaller tires but 31s aren't that huge.

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Ignorant no, realistic yes. What "hills" you are pulling 75+ in a lifted rig on stock gears?

are you saying your jeep isn't capable of going more than 75mph as it sits, or its hard to maintain it? If you literally max out at 75 she's definitely tired. If you struggle to pull hills and maintain 75 mph, that sounds pretty normal.

smokeyyank said:

Ignorant no, realistic yes. What "hills" you are pulling 75+ in a lifted rig on stock gears?

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Ignorant, yes. Nobody is talking about going uphill at 75 - he clearly states that is the max speed "ON THE INTERSTATE". That is below the speed limit! You are also confusing "top speed" and "safe speed", which are two very different things. An XJ with a small lift, 31" tires, and stock gearing should have no problem going faster than 75 on the freeway.

31" tires and a 3" lift is not very much. If we were talking about 35s and a 6" lift it would be a bit different.

But yes, my XJ can certainly do 75 uphill no problem, and more than that.

If you haven't I would say refresh all your ignition wires, plugs, cap rotor, coil maybe, air filter and oils. Anything that restricts rolling resistance will take it's toll on the power the skinny pedal can deliver.

Then if you really want more power on the top end a new cat/ muffler back, the least restrictive set up possible. Your half way there with a snorkel. You also have a good bumper, but I assume that beast has some lbs with the winch.

Beyond this gears can help lots but I wouldnt regear for 31s, nope. I ran 32" Kevlars on stock gears and that was 80mph 2900rpm. Gears around town sure it'll pep up, but going deeper on small tires I would advise against. Throw the jeep in 3rd for a week and see how you like it, thats not a bad compoarisson other than off the line. If you can drive someone's local jeep that's regeared , itll give you an idea as well. Deeper gears = higher rpm mostly. Smokey mentioned a good calculator that you can play with all kinds of set ups.

Stroker is like 5k$ area unless you/friend can do much yourself, plus lots of quarks to tune. With multiple levels of strokers power to wallet ratio is better, but you'd still better really want it. I do think anyone invested in more power will gain the most from a stroker for what you'll pay. Ide spend coin boosting a stroker before I ever considered 'LS

Ls swap is a whole other ball game. Your talking Big Money, big torque in a lil unibody. Read more on these and you'll see some awesome builds that even trussed/caged/braced.... vehicles have twisted. The wiring and parts up keep is a hodgepodge, quite the build process. I would loose the lustful idea unless you can save serious coin, but it would definitely sound badass lol.

Anywho that's my 2cents, best of luck sir:wave:

Number21 said:

Ignorant, yes. Nobody is talking about going uphill at 75 - he clearly states that is the max speed "ON THE INTERSTATE". That is below the speed limit! You are also confusing "top speed" and "safe speed", which are two very different things. An XJ with a small lift, 31" tires, and stock gearing should have no problem going faster than 75 on the freeway.

31" tires and a 3" lift is not very much. If we were talking about 35s and a 6" lift it would be a bit different.

But yes, my XJ can certainly do 75 uphill no problem, and more than that.

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Cool brah......

I did the LS1 swap and love it. I love rock climbing and listening to the v8 as I climb. Its worth it, what I did was found a 2001 z28 and it had everything I need to do the swap. Tim consuming but nice

Oh yeah and it hauls but on the street, do what you want to do that's what I did. No regrets

My experience, 31's and stock gears just sucks. There was a noticeable improvement going back down to 235/75/15 tires.
I bet re-gearing to 4.10 will get you up the Appalachians. with 31's, 4.10 gears are comparable to stock - and stock got me around the Rockies just fine.