Jeep LS Swap Part 1: Introduction

If you had told 20-something me that I would stop racing, only have one operational SR20-powered vehicle (an off-road buggy, no less), daily drive a RWD V8 pony car, and spend most of my free budget swapping a smog legal GM Gen III Small Block (aka LS engine) into a Jeep, that asshole that was once me would’ve laughed at you. Sorry about that, youth brings arrogance.

Nonetheless, I find myself embarking on the painful journey of not only an engine swap, but a cross-manufacturer engine swap in a street legal (mostly, don’t talk to me about mudflaps) California vehicle. While many of you may not necessarily be interested in an off-road project, there will definitely be a lot of useful information in this swap that pertains to any vehicle, and the information on a smog legal LS swap in California isn’t the most complete or current. Not doing a California street legal LS swap either? I’m sure you’ll still have plenty of opportunity to laugh at me while I shoehorn a V8 into a cramped Jeep and then attempt to convince bureaucrats that everything’s okay. Honest sir, this thing is 100% stock. Bolts right in.

Behold! Jeep’s “High Output” 190hp 4.0L I6 in all of its muddy glory! Never before (well, since the late 90s) has so much external size resulted in so little displacement and power output. While reliable, it leaves a lot to be desired when it comes to power, is hilariously bad on fuel, and packaging efficiency is of the finest Soviet-just-make-everything-thicker-shit’ll-be-fine engineering practice. To the left you can see my attempts to keep the upper coolant hose alive since Jeep decided to place it in direct contact with, well, everything. The plastic rail to the right of the valve cover is the primary engine sensor and injector harness. More on that later.

Before we dive into the particulars about the “LS” swap (more on that later), it’s best I introduce you to what’s been an ongoing project for the past 4 years for me. Just because I stopped racing, doesn’t mean I’ve stopped ruining turning perfectly good street vehicles into something the original manufacturer never intended.

Mud Hills, Ocotillo, CA

My 1997 Jeep Cherokee Sport, or the XJ as its known in the Jeeping world, is a little rough around the edges, but is perfect for my intended purposes. Bought for $600 from some kid in Carlsbad (it had a smashed front right header panel, a dead water pump, and a lot of AA pamphlets in it), it was the S13 of the off-roading world when I bought it: cheap fun with enough aftermarket support to build to any level you want. Like the S13, some yahoo wrote an article about how cheap and capable they were, and finding one for a song isn’t possible anymore. Total budget so far? $4200. Hopefully it won’t double by the time I’m done. Paint? Yeah, it has some left. Straight body panels? Overrated. Air conditioning? Arctic: I may be uncivilized, but I’m not a Neanderthal.

I may be ill-adjusted, but I’m not an animal. My trail home away from home doesn’t have roof top tents, refrigerators and a bunch of plastic gear bolted to a rack, but it is very comfortable and capable for a family of 4 (and 2 dogs) to have a week-long vacation somewhere remote.

The suspension/drivetrain on my XJ is well-sorted. Mods so far are lockers and 4.56:1 gearing for the stock Chrysler 8.25 and Dana 30, home-built truss and inner C reinforcement on the Dana 30, an Iron Rock Off Road (IRO) Rock Link long arm kit, IRO over the knuckle steering, IRO track bar (modified for zero bumpsteer with the over the knuckle steering), Rubicon Express 5.5” lift springs, home-built boomerang rear leaf spring shackles, 33×12.50×15 General Grabber X3s on beadlock wheels and Fox IFP 2.0s front and rear. Useable (i.e., tires or frame don’t act as bumpstops and the vehicle can turn full lock without contact) suspension cycles 13.5” rear and 16” front. With remote reservoir Fox 2.0 Factory Series shocks and long-travel suspension links, this XJ can maintain 40mph over large whoop sections, yet still crawl comfortably maintaining reasonable speed over the ever present pumpkin-sized rocks that present no challenge to a well-sorted rig but will beat the occupants senseless on an all-day trail. The small-ish shocks will fade on long high-speed desert runs, but these are few and far between and do not pose much of a limitation for most recreational trips.

Over the years, my Jeep has outgrown the “flex rock” on my property. There’s 4’ of vertical separation between right front and left rear with about 3” of bump travel remaining in the rear and a similar amount of droop up front. Maybe more cinder blocks?


  1. Holy shit! Every time I come to this site “to just see what’s happening” I run into a project I’ve been thinking of doing myself for a while. Somewhere in this computer I have a massive bookmark folder (I do need to thin them out) titled “swap “LS” engine into different 4X4s”
    I think I was researching ZJ and WJ Grand Cherokees (I want the front and rear coil suspension) And quite a number of Land Rovers.
    Looking forward to this build.

    1. WJ is the current sweet spot in new vs capability vs cost. Gas tank hangs waaaay low, but can be tucked, and the suspension is JK version 0.75 and isn’t terribly hard to swap JK axles into. ZJs are piles, but if you’re not keeping any of the drivetrain and electronics, not terrible. Both come with shitty stock axles (generally LP D30 and D44A, A for aluminum pumpkin), so don’t plan on keeping them for long if rock crawling.

  2. The problem I run into with the different generations of Grand Cherokee (or jeeps in general) You get a relatively reliable “engine” (318, 360, 4.0, 4.2) As long as you pay very close attention to heat management. And wiring harnesses that could best be described as Soviet Chinese tractor.
    Or hand grenades with the pins pulled most of the way out (4.7, 3.7) but kinda stout transmissions. But in all generations the axles are pretty weak. The 30s not that bad if you truss and sleeve and chromoly the entire thing. An explorer 8.8 swap is an easy and cheap upgrade for the rear.
    I was planning on the WJ with the 4.0. Hanging the spare tire on a bumper or roof. Cutting out the spare tire well and tucking the gas tank. Then doing the stroker. But as you said you are already $5Gs in the hole for that. And you still have to deal with (more) heat and the wiring harnesses. That’s why I’m kinda looking forward o this project. I know it won’t be a definitive swap and all. But here in Arizona they (phoenix) basically follow California’s emissions laws. I’ve asked the smog referee about doing this is the engine has to match the vehicle class (no CTSV supercharged engines) and it had to retain all the emissions equipment. But he had no list or detailed answer to what “emissions equipment” includes.

    1. All of it needs to be there. Basically, if it sets off a MIL, it’s required. AZ is a little less stringent on engine changes, but…

      D30s are stronger than you think, just don’t be stupid with it. Locked on 33s with stock shafts (welded 760x caps) for years now, no issues. If you’re jammed in a spot, back out or winch. If you have to give it more than 1/4 throttle before wheelspin, you’re probably gonna break something. The truss went on when I got a set of 3 tube bypasses for it, but turned out an XJ doesn’t have the axle width to clear them without touching a tire or the frame or both. The Fox Factory 2.0s baaaaarely fit.

  3. You left out the LQ9, visually indiscernible from the LQ4, and should have landed in the correct weight/emissions class. Thus an LQ4 branded as an LQ9 should fly. If I were to guess though, this 5.3 will run cooler than the 4.0 and your cooling issues should be behind you. I wouldn’t crack the motor open myself, keep the magic smoke inside. They run forever. I’d also toss that 4L60 time bomb in favor of a 4L80. Either way I think you’re going to like this rig once it’s swapped.

    1. Yeah, completely forgot about the LQ9, but it’s pretty hard to find as well, people will fight you in the junkyard if you do find one, and I bought a donor that didn’t have it, so shoot me. Updated the article. 🙂

      Yeah, cooling should be better with the 5.3 since it’s an engine designed in the last 20 years, has aluminum heads, and doesn’t burn huge amounts of gasoline to make small amounts of power.

      Motor should’ve been cracked open. There were timebombs in there. Stay tuned for part 2. 🙂

      4L60 to 4L80 swap may be something for the future, but it’s physically much larger and the mounts I’m using were designed with the 60. Clearance for the driveshaft, links and all-important cats will be bad enough as it is. There’s also the need to re-parameter the PCM for 4L80 operation, which I’m told is something the ref might check. That being said, the original 4L60E has a shorter 1st for better crawling, and motivated that pig of a suburban around for well over 100k miles (including RV towing) and still shifted firm when I drove it home. It’ll get refreshed while it’s out, but I think it’ll be just fine for mild towing (tent trailer at most) and barely warmed over 5.3.

      1. I’m curious what a smog ref would look for on a reflashed PCM? Does he know it’s modified and fails you on that? Transmissions aren’t emissions items and that segment can be swapped without touching anything emissions related or VIN related. Speaking of VIN, how does that work in a swap in CA? I don’t think you can punch a Jeep VIN into a GM PCM (never tried). I’m curious what mounts and parts you’ll be going with here, but I’m guessing that all comes out in part 2.

        1. Transmissions aren’t, but the sensors involved will throw check engine lights, therefore under their purview. Either way, the 4L60E is plenty for a 4000lb Jeep that will rarely see 5000rpm, and the gearing better suited as well.

          VIN is easy: they add a new barcode/label over the existing emissions label so when the tech scans it, it comes up as 2003 Chevy Suburban.

  4. Steve any thoughts on how the BSFC/MPG may change based on the swap you’re doing? Seems like the EPA ratings put the Suburban as worse fuel economy than the Cherokee but I realize there’s a decent weight savings in the Cherokee.

    1. The stock 3200lb Cherokee 4×4 on 28″ tires (13/18) was marginally better than the 5500lb Suburban 4×4 on 30.6″ tires (13/17), sure. The Tahoe was 14/18 so better/same than the Cherokee and still almost 2000lbs heavier than the stock Cherokee. Currently, my XJ gets 12-14mpg mixed driving, and a ridiculous 9-11mpg when wheeling. A large part of this is due to heatsoak: the Cherokee’s ECU massively retards timing to protect the motor, which then increases heatsoak, and it also bumps engine idle speed to make the mechanical fan run faster, which forces me to use the brakes more to compensate and makes even more heat. It’s a shit show to say the least.

      My assumption is the Cherokee will get similar mileage to the stock Tahoe despite the short gearing, large MTs and extra weight from armor. Being able to run a large electric fan (no slim fan that will fit will provide nearly enough airflow for the 4.0) and larger radiator will help a TON to keep fuel economy reasonable. Factory ECUs do stupid things to protect the motor from heat, and a negatively sliding timing curve is one of them.

  5. Great job writing this. I dig your style and look forward to the rest of the project. I just crammed a supercharged LS3 into my XJ and it will be 49 state legal, couldnt waste my time with CA approved headers… It can be done but might not be worth it for most.

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