The TJ’s 4-cylinder engine is in process of being removed for replacement with a Magnum 5.9L from a Jeep Grand Cherokee. The more body parts that are removed the easier it is to get to everything. Take time to label everything. (Photo Courtesy Ben Mann)
As with any swap choice, many choices do not make sense because of complexity or poor aftermarket support. What may seem like a good idea at the time will turn into a money pit and time waster. A few companies, such as Novak Conversions and Advance Adapters, specialize in Jeep engine conversions; they make components ranging from adapters to radiators that make a conversion almost easy. Keep in mind that any swap will have its challenges. The key to success in a swap, even before the first bolt is removed, is preparation and planning. Because there are so many options and combinations, it’s nearly impossible to give full step-by-step instructions for a swap; I will provide some ideas and common practices.
Jeep to Jeep Conversion: 2.5L and 2.4L to 4.0L
Swapping from a Jeep 4-cylinder to a 4.0L is a rather straightforward process and is much easier if a donor Jeep is available. Enough differences are present to make finding parts afterward extremely difficult and expensive. Exact-swap processes are a bit different when using engines from other Jeeps; because the model years vary slightly; it’s another reason to get everything possible from the donor Jeep. Many folks who have done this swap recommend staying within a year or two for maximum compatibility. Engine mounts, exhaust, power steering lines, and much more will be impacted from the swap. Certain 4-cylinder transmissions will not mate to the 4.0L, namely the AX-5.
Non-Jeep Conversions
Swapping in a non-factory engine brings an array of potential issues. Fitting and mounting the engine, determining the transmission, and finding adapters, mounts, and radiators are just the tip of the iceberg. Many hidden gotchas can appear that will eat up a lot of time and money. Almost all of the factory gauges operate from input of the PCM; in most swaps, replacing the entire gauge cluster with aftermarket gauges is necessary. Fuel lines and sizes, transmission shifter location, and power-steering connections are additional items that will need addressing. The steering shaft, front axle, frame rails, and firewall are all elements that can interfere with a swap. It’s a given that a non-Jeep swap will require a custom exhaust system. There isn’t a lot of room under a TJ; snaking larger-diameter exhaust tubes, especially a dual exhaust, can get very tricky.
GM V-6 and V-8
These two engines can add some incredible power to the TJ, and swapping a modern GM engine is easier than ever. Of course, swapping a pre-computer, non-fuel-injected engine may be the first thought of some Jeep owners, especially those who have performed swaps in earlier-era Jeeps. In many areas that require emissions inspections, swapping a non-computer, non-fuel-injected engine for a TJ engine may cause the inspection to fail. Some people believe that using an earlier-style engine will be less expensive and result in more power, but swapping modern, emissions-friendly engines can often cost less and result in more power and efficiency. Emissions laws often permit engine swaps only when the donor engine is the same year or newer than the recipient, depending on the state where it will be registered.
The Generation III and later V-8 from GM is so compatible in the Jeep that a swap can be easy, clean, and efficient. Novak Conversions has been a leader in engine swaps in Jeeps for many years and it has adapted to the changing times to provide solutions for newer Jeeps. The Gen III and later engines still use the same bellhousing pattern as in the past; attaching an older manual or automatic is rather simple.
Novak indicates that obtaining the engine and transmission from the donor vehicle, along with all of its electronics, is a key step for success. The PCM can be custom programmed to match the particular transmission, especially a manual transmission. Of all swaps, the GM V-8 is believed to be the most simple. Obvious items that would be impacted (other than those that are part of the engine/transmission combination) are radiator, driveshafts, fuel lines, gauges, and much more.
The Generation III and later GM V-8 engines are some of the easiest swap engines available. When mated with a GM transmission, which easily adapted to the NP231 or NV241, the power and reliability of this combination will make any Jeep owner happy. Custom computer programming is readily obtained for a (nearly) plug-and-play conversion. (Photo Courtesy Novak Conversions)
Mopar, Including Hemi
The Hemi swap is more of a novelty rather than being practical. The cost of the engine plus the long list of swap details makes this engine an impractical candidate for a TJ. Companies such as AEV specialize in Hemi conversions and produce a conversion kit that makes the swap much cleaner and easier. For those with money to burn, Mopar offers crate Hemi engines that are complete and ready for a custom installation. This kind of engine swap requires a compatible transmission and stronger axles capable of dealing with the power output.
The Mopar Magnum 5.9L that was used in Dodge vehicles, including the Jeep Grand Cherokee, offers an almost Jeep-to-Jeep swap. This engine is based upon the older Mopar LA engine that offers excellent power and torque in a modern-style engine. This engine was mated to a NV3550 transmission using a NP 231 transfer case. (Photo Courtesy Ben Mann)
Using a Mopar V-8 such as a Magnum 5.2L or 5.9L from a Jeep Grand Cherokee or Dodge vehicle is a common swap that can keep the Jeep “feel.” Advance Adapters makes mounts, radiators, and transmission/transfer case adapters for this swap. Like most other swaps, obtaining as much from the donor vehicle as possible will ease the installation. Companies such as Auto Computer Exchange can customize the engine’s ECM to match the Jeep.
Diesel
There is a certain group of individuals who have a deep-rooted love for a diesel engine in a Jeep. It is a polarized argument; you’re either on one side or the other. It’s similar to the old Ford versus Chevy and chocolate versus vanilla arguments. Never a clear winner; it just comes down to preference.
Diesel engines offer unique characteristics when compared to gasoline engines, especially in the low-end torque and high-fuel-efficiency categories. By design, the diesel engine offers much more low-RPM torque than a similarly sized gasoline engine. The demands of a trail Jeep are well matched to a diesel, sometimes so much so that some people question why it was never available from the factory.
The expense of the diesel engine and the items required to do the swap often exceed the amount of money saved by the gain in fuel efficiency. For those who really do want to swap in a diesel, the Cummins 4BT engine is a favorite among the Jeep community. When taken care of, the 4BT engine is known for exceeding 500,000 miles and can be converted to run alternative fuels.
Typically, a transmission swap is required with a diesel conversion. Popular transmissions are 4L80e HD automatic transmission or NV4500 manual transmission. Many other components, including radiators, exhaust, and electronics, must be custom matched to the swap for success. Jeff Daniel’s Jeep Customization and Bruiser Conversions is a well-known shop for diesel swaps.
Diesel swaps are popular among certain groups of Jeep owners. The most popular diesel for swapping is the Cummins 4BT engine, which is sized well for the TJ. It puts out impressive torque, which is especially useful on the trail, as well as excellent fuel mileage on the street. Several ways of mounting and adapting are available for diesel engines that make this swap not too difficult.
Putting It All Together
The project Jeep is being built for performance on- and off-road. This particular application does not require a massive amount