How to LS Swap an XJ Jeep Cherokee (photos)
The LS engine platform has come to be known as the best bang for the buck engine swap. With stock LS engines easily surpassing the performance of the largest 4.0L Straight-Six Jeep engine as found in the XJ Cherokee, they are a great solution for increased power without sacrificing reliability.
1. Motor Mounts
To precisely place an LS engine into the engine bay of an XJ Cherokee, it is important to use XJ specific LS frame brackets and engine block plates like those supplied by Novak Conversions. Because of the relatively small size of the engine bay combined with the low hood line of the XJ, placement of the engine is crucial if you are going to get it all to fit. The frame brackets require no cutting or welding but need to be drilled and mounted to the frame rails/unibody. It is worth noting that an LS car engine is preferable over a Vortec truck engine as the intake and accessories sit lower to clear the hood. However, one can always change out the intake and accessory drive of a truck engine with those of a car if necessary.
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2. Accessory Drive
As mentioned, LS engines from F-body cars as well as Corvettes and GTOs are preferable because of their accessory drive configurations, but F-body and GTO layouts will need a slight rearrangement by swapping positions of the power steering pump and alternator (like the Corvette setup). This will ensure the are no clearance issues with the steering gear. Additionally, an air-conditioning compressor relocation kit will be needed to move the compressor closer to the passenger side cylinder head in order to prevent interference with the frame rail.
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3. Transmission & Transfer Case Choices
The Jeep XJ was offered with various transmission options throughout its production run, but nearly all of them are considered too fragile for the output that an LS engine will produce. That said, the factory Aisin AX15 5-speed manual transmission is quite stout and has proven to match up well with a vehicle that will be used on the street and on medium-duty trails. As per the usual LS swap, the TH350/400, 700R4, and 4L60E automatic transmissions work well and are adaptable to the standard transfer cases (NP207/241/232) with the correct adapter plates. If you are going to be putting your XJ through some serious off-road workouts, consider the low-geared 4-speed SM420 or SM465 transmissions that will allow your Jeep to climb even the most treacherous terrain.
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4. Cooling
It probably comes as no surprise that the failure-prone factory radiator with its remote surge tank will need replacing when swapping to an LS V8. While there are no cheap factory replacements that can be pulled from another vehicle, Kryoflow Cooling and Griffin Thermal Products offer XJ radiators with standard filler necks and LS-specific outlets that easily bolt in. Griffin even offers a full kit that includes dual electric fans to make the swap that much easier. However, it will be up to owners to source their own hoses that can be adapted to this application as it seems there are no LS swap specific hoses currently available.
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5. Exhaust
Unfortunately, the majority of the exhaust system for an XJ LS swap is a custom venture as no company is currently producing a complete exhaust kit for this application. That said, Novak Conversions does offer a set of block-hugger headers that will get you started on the right foot. These specific headers fit neatly within the cramped engine bay with the collector flanges exiting in ideal positions to build the rest of your exhaust. It is recommended that each header is merged with a y-pipe to allow for a single pipe with your choice of cat, muffler, and tip exiting the rear of the car.
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6. Fueling
A bright spot in the original Jeep components is the fuel system on all 1987 to 2001 XJ models. The factory fuel pump is capable of producing 100 psi of fuel pressure (which is regulated down to 40-45 for the factory 2.5L and 4.0L engines), so the entire fuel system is very well capable of supplying an LS engine approximately 60 psi with a proper fuel pressure regulator. If working with an older carbureted model, the components from a fuel-injected donor can be swapped over, or an external electric fuel pump can be adapted to get fuel up to the engine.
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7. Wiring & ECM
For pre-1996 OBD-I XJ models, it is suggested that the entire engine wiring harness, ECM, and transmission control module be removed from the car. Similarly, the wiring harness and PCM can be removed from 1996-2001 models, but it is recommended that the PCM and wiring be left in place as a piggyback to the operate the digital gauges if not switching to a GM compatible gauge cluster. As with all LS swaps, there are endless wiring options from numerous companies that specialize in custom harnesses and ECMs for the intended application. As an alternative, a compatible wiring harness and ECM can be plucked from a junkyard on the cheap but will require the ECM be reflashed by a tuner to disable the anti-theft system that is in place from the donor vehicle.
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8. Odds & Ends
A lifted XJ (2" or more) provides a good amount of clearance between the front axle and oil pan, but it is not a bad idea to install a Vortec truck oil pan for additional clearance. The GM power steering pump is compatible with the Jeep's power steering gear by simply using the correct supply and return lines as found at any local parts store. The stock gas pedal/throttle cable will work for cable operated engines but will need to be swapped out for a fly-by-wire throttle pedal if using a newer engine. Air intakes work best by using a 90-degree elbow coupled with a cone-style air filter. Stock front and rear driveshafts typically work with LS conversions, but depending on the type of driving that will be done, may require slight modifications to alter the overall length. In general, the XJ platform easily accepts the LS powertrain without the use of too many custom parts.
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For help with maintenance and service on your Jeep, check out the how-to section of JK-Forum.com