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  4. TJ LS1 V-8 Conversion: Part 1

TJ LS1 V-8 Conversion: Part 1

Bruce W. SmithPhotographer, Writer

More power. More performance. More smiles. Those are the common denominators among Jeep owners who dream of slipping a healthy V-8 into the engine bay of their 4.0L TJs. Transplanting engines has been around since the dawn of powered vehicles, and when it comes to ditching one engine for another in Jeeps, well, there are more combinations than there are trails to wheel. That’s because if one puts their mind to it, just about any powerplant can be married into a Jeep. It all depends on how deep one is willing to dig into those coin pockets, how much time one is willing to expend, and what resources are available to make the vision a reality.

In our case, it’s nixing a 16-year-old trail-worn 4.0L under the hood of a rockcrawling ’00 Jeep TJ and replacing it with an EFI Chevy LS1. Although our goal isn’t that lofty, our financial pockets are pathetically shallow, so we leaned on the expert technicians at Dunks Performance in Springfield, Oregon, who have built a number of custom Jeeps in the last couple years. They showed us how to swap an GM LS1 into a Jeep TJ and how to minimize time and money making when doing it.

Decisions, Decisions
Dunks suggested a GM LS1 out of a ’99-’02 junkyard Camaro, GTO, or TransAm because the direct-port-injected 5.7L delivers excellent power for use in a Jeep. The later of those years are said to make about 310 rear-wheel horsepower and somewhere in the neighborhood of 350 hp at the flywheel. The ’01 and ’12 years are the junkyard gems for such a swap and were the recipient of the same injectors and intake manifold used in the Corvette LS6, as well as other shared power components, including the Corvette’s exhaust manifolds. That vintage LS1 also used a high-volume version of the mass airflow (MAF) sensor that allows the Powertrain Control Module to increase intake volume and adjust to a wider range of air temperatures. We sourced a complete ’02 engine from a local salvage yard for $1,800 that had less than 150k miles on it. The engine checked in excellent condition, saving us serious coin by not having to do a complete rebuild.

Holley Hook-Up
The biggest roadblock swapping in the GM EFI V-8 was engine wiring—the Jeep’s engine control computer doesn’t speak GM. Salvage yards remove engines in the fastest, easiest way possible and seldom, if ever, take time to unplug wiring harnesses. They cut them off and yank the engine. Fortunately, Holley Performance offers a complete plug-and-play stand-alone EFI system that’s carefully engineered and packaged for GM LS1/LS6 engine swaps.

Holley’s HP EFI ECU & Harness Kit (PN 550-602N) is an LS1 transplanter’s dream come true. It offers the laptop-programmable ECU, with all the sensor plugs, power, and ground leads neatly labeled, as well as a detailed instruction manual and software to run on a laptop. Everything is there to easily make the early LS1s (those using a 24-tooth crank sensor) run perfectly happy in a TJ.

Cooling Concerns
Another hurdle to get over with V-8 transplants is keeping an LS1 cool while working it hard at slow speeds. Flex-a-lite offers its LS Conversion radiator, and it’s specifically designed for a TJ LS1 V-8 swap. The direct bolt-in unit has a 15-inch Black Magic electric fan that flows 3,000 cfm through the aluminum double-row core’s 1-inch tubes, more than doubling the stock Jeep radiator’s cooling capacity and efficiency.

Flex-a-lite also offers a direct-fit TJ oil cooler kit as an option, which we chose for this transplant. The TransLife kit includes a six-pass transmission cooler and the brackets necessary to easily install the cooler directly to the vehicle. Using an auxiliary transmission cooler brings the cooling outside of the radiator side tank for better cooling.

You could use the electronically controlled automatic (4L60E) that came in the donor car if you really want a juice tranny. However, to keep costs down and reduce any electrical-related transmission issues on the trail, we opted to go old-school with a GM TH400. These three-speed automatics are bulletproof and simple, and TH400s out of those same-era motorhomes are excellent choices for Jeep/GM V-8 swaps.

We bought an early ‘80s TH400 from the same place we found the LS1 for a song and had it rebuilt by Springfield (Oregon) Automotive using a B&M rebuild kit, stock valve body, brass bushings, and a new steel direct drum and 34-element heavy-duty sprag clutch. It’s nothing fancy, but it’s very reliable.

Power Split
We turned to Advance Adapters for the TJ LS1 V-8 engine mounts, and the best transfer case ever built for high-performance 4x4s: the Atlas 2. This gear-driven two-speed unit, first built in 1995, is legendary for its strength and performance. Hard-core rockcrawlers and 4x4 racers with high-horsepower rigs worldwide sing its praises and count on it to pull them through the worst conditions.

The twin-stick unit offers lower gear ratios than other transfer cases, and it’s fully synchronized so the driver can shift on the fly between high- and low-range in 4WD or 2WD. It has the option of five gear ratios from 2.0:1 to 5.0:1; multiple drop, yoke and tailhousing configurations; and shifter options to specifically fit a wide range of vehicles including the TJ. It allows you to shift into front-wheel-drive low-range, which can be beneficial in really tight off-road maneuvering situations and in snow.

Go Time
Eric Dunks, shop-owner Mike Dunk’s younger brother, is an ASE master mechanic and certified Chrysler/Jeep technician, and fellow Dunks tech and custom fabricator, Casey Castle, dove into our TJ with vigor. This was the third custom GM V-8 Jeep conversion they’d done in the last year, so they knew the game and the plan of attack.

In this first of a two-part story, we focused on the finer aspects of removing the old Jeep 4.0L, manual transmission, and transfer case, and setting up the new components. Part 2 will cover engine wiring and programing, gauges, driveshafts, and the exhaust system so we can fire up the LS1 and take our TJ for a test drive. Stay tuned!

A Camaro LS1 is a great V-8 replacement for those who want to ditch the stock Jeep 4.0L inline-six.

Eric Dunks helps snake the 4.0L six-cylinder, transmission, and transfer case out of our ’00 TJ as Casey Castle mans the forklift. Having a well-equipped shop makes an engine transplant like this a lot easier than working in one’s home garage.

None of the Jeep 4.0L’s wiring system will work with the EFI LS1, so we stripped all of the electrical components out of the TJ’s engine compartment.

Although our TJ had seen a lot of front frame and suspension mods, the engine bay had been left untouched, so Eric gave it a good pressure washing before starting the swap. The rainbow is a good omen.

Casey’s first order of business is prepping the TJ’s engine bay and frame, which includes cutting off the factory engine mounts, then grinding the frame rails smooth.

Advance Adapters makes mating an LS1 inside a Jeep TJ engine compartment easy with these custom-fabricated engine mounts. These are a must for such a conversion.

The LS1 V-8 is 108 pounds lighter than the 4.0L six that came out of our TJ, so the complete swap ends up being a wash when it comes to weight savings/gain.

This Holley LS1 Retro-fit oil pan is designed to provide more clearance at the front half of the oil pan and works great with the TJ chassis. The pan is baffled so it keeps the oil where it needs to be on steep off-road angles.

Our junkyard ’02 LS1 was in good shape with relatively low miles. Eric freshened it up with the bare essentials: new timing chain, gaskets, AC Delco HL-124 roller lifters, and a hydraulic XFI RPM (PN 54-408-11) Comp Cam that has a special off-road grind to give the LS1 better low-end torque and better mpg over the stock Gen IV LS1 bumpstick.

A nice combo for trail use is the LS1 backed by an early ’80s TH400. Our trans was rebuilt with the basic B&M kit, along with a new steel direct-drum and 34-element Sprague.

Cooling is critical in any Jeep V-8 swap. Flex-a-lite’s new LS1 TJ drop-in radiator is equipped with thermostatically controlled electric fan with more than double the cooling capacity of the OEM radiator. The Flex-a-lite kit is designed specifically for this application.

We spared no expense on the new Advance Adapters transfer case. This Atlas 2 was custom-built to our needs with a 3.8:1 ratio, as well as yokes, offset, shifter, and adapters to fit the ’84 TH400 going into our TJ.

Our LS1 swap wouldn’t even be considered had it not been for this stand-alone engine wiring harness kit (PN 550-602N LS) from Holley. It’s designed to work with pre-’06 GM EFI V-8s that use the 24-tooth crank wheel. Kit is plug-and-play with its own CPU and easy-to-follow detailed instructions.

Make sure your used LS1 comes with all of the sensors, including idle air control and throttle position (TP) sensors on the throttle body (shown), the knock sensors (under the intake manifold), and the pigtails, along with the coil packs and throttle body sensors (shown). Buying new sensors will cost several hundred dollars, and replacement coil packs run about $90 apiece, making that “good deal” on an LS1 not so good after all.

Always make sure the LS1 you are buying has the Cam sensor, located on the block directly above the flywheel, the manifold absolute pressure (MAP) sensor on the intake and the aforementioned knock and TP sensors.

Here, Eric installs the OEM knock sensors on our engine prior to getting it ready for the first of what will be several trips in and out of our TJ’s engine bay.

Most of the LS1 sensors are not interchangeable among years, according to Eric, who is a certified ASE master mechanic and Chrysler/Jeep technician. “For example, the crankshaft sensor, located behind the starter, is black on pre-’06 engines with the 24-tooth wheel. LS1s built after that time used a 58-tooth pick-up wheel, and the sensors are grey. It’s always best to get an engine that has everything on it.”

We retained the stock LS1 exhaust manifolds (left), which were shared with the Corvette engine in ’01-‘02. Long-tube headers make the install much more difficult, and “shorty” headers (right) don’t flow any better than the factory LS1 manifolds—at least for our off-road application.

One clearance issue that will arise with the LS1/TH400 combo is that the stock exhaust hits the tranny’s wing ears. The ears will have to be trimmed back.

Casey’s method of trimming the TH400 ears is simple, fast, and effective: use a Sawzall. The tabs being removed aren’t needed for the TJ swap.

Clearance issues between the LS1 exhaust manifold outlet and TH400 housing is easily solved with a Sawzall. The cutting of the wings leave plenty of room to bolt on a custom exhaust system when the LS1 is in its new home.

Casey (left) and Eric discuss the LS1’s placement in the TJ engine compartment during the first pass. We took the engine in and out three times during the transplant process to make sure fitment and clearance issues were cleanly and efficiently addressed.

Although our TJ’s front frame horns had been replaced with tube, the actual placement of the LS1 on the Jeep chassis will be the same for a stock TJ.

Advance Adapters’ LS1 TJ engine mounting kit comes with special tabs (arrow) with a pin in each that drops into a hole in the Jeep frame, positioning the actual engine mount in the perfect location.

Once the Advance Adapters’ frame locating tabs are in place, Casey slides the fabricated LS1 engine frame mounts on the chassis to be tack welded.

Our engine frame mounts are tack-welded in place until the final fitment of the engine. That takes place after the transmission and transfer case are in proper position later in the swap process.

Casey used his favorite adjustment tool to flatten a body seam that is too close to the TH400 case. The only other area around the TJ firewall that needs some fine-tuning was on the passenger side where it touched the LS1’s valve cover.

The LS1 fit is tight, but with a small adjustment made to the body seam between the floor and firewall, it parks in the TJ just fine.

After any firewall clearance issues are handled and the engine frame mounts are in position, we spent a couple hours cleaning and painting the engine compartment. We like things to look nice and neat.

Advance provides different spacers for the TH400/Atlas 2 match up depending on the transmission’s output shaft length. Our transmission required the MR AS-0404 1 1/4-inch thick spacer with 1 1/4-inch AS-6401 adapter.

Adapters bolted on, sensors installed, and the trans and transfer case ready for their new home, Eric bolts on the last of the LS1 parts that are best installed outside of the TJ.

One of the best investments in new parts for a TJ LS1 swap is buying this GM CTS-V Accessory Drive package (PN NAL19155066) that includes self-regulating alternator, power steering pump, power steering reservoir, brackets, and other necessary items for a clean swap. The accessory drive kit provides maximum space between the engine and the radiator.

Now that the engine is in its final resting location, we installed the Flex-a-lite radiator assembly. It works slick with the CTS-V accessory drive, providing just the right amount of fan-to-engine clearance. Another excellent combination on the TJ LS1 is using the water pump, drive housing, and crank pulley pulled off any of the car LS3/6.2L engines.

Advance Adapters takes a lot of the drama out of the LS1 V-8 swap with their custom-fabricated adapters that perfectly clock the Atlas 2 with the TH400/LS1 so the TC fits under the TJ in the perfect position.

The Atlas 2 shift linkages can be adjusted and modified to fit just about any location. Casey cut the brass center bushing that holds the shift levers in half. Doing so brought the twin sticks in proper alignment with the stock TJ center console, making the install look factory when our LS1 swap is finished.

It’s tight. The size and configuration of the Atlas 2 requires a 2-inch body lift and 4-inch suspension lift, which our host TJ, a dedicated rockcrawler, already had in place before starting the V-8 swap. Here Eric slides the TC into position from underneath while Casey helps guide it in from inside the TJ. A little hydraulic scissor lift table is a godsend when doing this type of work.

The engine is in. The radiator is in. The transmission and transfer case are in. It’s looking good! Next we’ll address the engine wiring, fuel system, A/C plumbing, and instrumentation. Stay tuned!