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CHAPTER 2

FACTORY ENGINES AND ENGINE SWAPS

It’s commonplace for owners of classic Jeeps such as AMC-era CJs (1972–1986) and earlier to swap engines because of the low-performance engine options in those years. In addition, swapping a tired old engine in a Jeep that’s 30 or more years old is quite simple thanks to simple computer controls or even a lack of computer controls altogether. These engines often have simple emissions controls and may be exempt from emissions inspections.

In the past, swapping a small-block Chevy into an older Jeep such as an AMC-era CJ was common, easy, and relatively inexpensive. The modern TJ presents some complexity with a swap because emissions requirements are stiffer now. A swap with an engine of the same year or newer will often satisfy emissions requirements. (Photo Courtesy Ben Mann)

Engine swapping is much less common with the TJ. It’s only recently that changing engines has become more popular because of the TJ’s age. In many parts of the United States, vehicles are required to pass emissions testing that can present a challenge to the Jeep owner who hasn’t thought the swap through. In this chapter, I will explore swapping engines in greater detail and provide some guidelines to help with planning.

Factory Engines

Only three engines were offered with the TJ series: two different 4-cylinder models and one 6-cylinder. All were good engines. Unlike the series before the TJ, all of the engines offered used modern multi-port fuel injection (MPFI) that improved reliability and performance. The end of the Wrangler TJ series also marked the last use of the AMC engine, the 4.0L, which was replaced with the Chrysler 3.8L and 3.6L Pentastar V-6 of the JK series.

The Power Control Module

Perhaps before jumping into engines, discussing the Power Control Module (PCM) might be prudent. As modern vehicles evolved, the introduction and development of computerized systems increased their presence to the point that almost all of a vehicle’s systems are controlled or monitored by the PCM. If you have had the pleasure of owning a CJ, you may understand the simple nature of its computer-less system; it’s easy to troubleshoot and diagnose problems. While the complexity of the newer systems can seem daunting, these systems allow components, especially the engine, to produce more power while maintaining efficiency and clean operation. The PCM in the TJ years is mounted on the passenger’s side of the firewall in the engine compartment. It operates, monitors, and adjusts most of the engine functions, including spark timing, air-fuel ratio, idle speed, and much more.

The Chrysler Pentastar V-6 is the latest engine found in the JK Wrangler. The 3.6L has a smaller displacement than the 4.0L but thanks to modern technology, such as variable valve timing and dual overhead cams, this small engine puts out an impressive 285 hp, a big jump over the 190 hp of the 4.0L.

The power control module (PCM) controls and monitors almost all of the engine operations, making the engine more efficient and producing optimum power output. These modules are easily replaced in the event of a failure even though they are extremely reliable. The factory attempts to find a balance of performance versus efficiency. This allows the aftermarket to make add-ons to the PCM to improve performance.

2.5L MPFI 4

The 2.5L is an AMC-built engine introduced in 1984 that was designed specifically for use in Jeep and Eagle vehicles. It shared some components and specs from the I-6; however, it is not a “cut down” version of the I-6. The version of the 2.5L used in the 1997–2002 TJ was an MPFI design and was labeled as the Power-Tech I-4. The engine produces 121 hp at 5,250 rpm and 139 ft-lbs of torque at 3,250 rpm. Even with its small horsepower and torque ratings, with the correct gearing and low range this engine will keep a Jeep moving on the trail without issue.

2.4L DHOC 4

The 16-valve 2.4L replaced the 2.5 in 2002 and continued until 2005. Running dual overhead cams and four valves per cylinder allowed the engine to produce 147 hp at 5,200 rpm and 165 ft-lbs of torque at 4,000 rpm. This engine (in a number of variations) was used in many Chrysler vehicles until it was discontinued completely in 2005, when Chrysler’s World Engine replaced it. Like the 2.5L, this small engine is capable of keeping a Jeep moving with the proper gears.

Both of the 4-cylinder engines perform as well as they can, which is very limiting in a TJ. The small-displacement engine struggles on the highway when larger tires are added to the Jeep and the gears aren’t addressed to correct the effective ratio. The underpowered engines really perform their best off-road when using the Jeep’s low range.

2.5L and 2.4L Performance Upgrades

Many argue that there isn’t much more to be pulled from the 2.5L or 2.4L without spending more than a 4.0L swap would cost. Many Jeep owners have reported that most upgrades available do not make the difference that justifies the expense. Often it is reported, in an unscientific way by Jeep owners, that the improvement in performance seems to diminish as the Jeep’s engine controls work to control fuel input/exhaust output effectively. They conclude that as the engine adjusts it eliminates any gains. The investment is not worth the gain.

Several companies make performance mufflers for the Jeep that are often part of a cat-back system. This one from Banks is on a 4-cylinder TJ; its free-flowing design adds a little horsepower and some added engine tone. The cost of these systems is often not worth the minimal gain. However, if the system is in need of a replacement, it might be a worthwhile replacement. Most cat-back systems are stainless steel for long life.

Performance computer chips offer improvements in varying conditions by adjusting spark timing and air/fuel ratio. Installation is simple and can be done in less than 30 minutes. Chips from Jet and Superchips are available in varying forms and stages for TJs of all years. These modules typically install at the PCM and are placed inline with one of the PCM’s plugs.

Clean, Less Restricted Air: A new or, even better, reusable-style air filter alone can improve engine performance. These filters allow increased airflow and improve throttle response as well as fuel mileage. K&N filters are possibly the most popular reusable, high-flow filters available.

Exhaust: PaceSetter makes a direct replacement header for the 2.5L and 2.4L that provides increased exhaust flow that results in performance improvement. In addition to the header, a few companies such as Banks make cat-back systems that improve exhaust from the catalytic converter to exhaust exit.

Computer Modules and Programmers: Adding a modified computer module to the Jeep can improve performance by altering the Jeep’s programming. These modules install easily but often require installation of a performance exhaust and lower-engine-temperature thermostat to achieve maximum performance. Jet Performance Products makes modules for the Jeep 2.5L that are available in multiple performance stages.

Gearing: Most agree that regearing a TJ with a 4-cylinder will provide the most noticeable improvement to performance compared to other modifications. Adding larger tires will drastically degrade engine performance because of the larger tires’ effect on overall ratio. Most 4-cylinder–equipped TJs came with 4.10:1 ratios; often, regearing to 4.88 or lower will bring life back to the small engine. Gearing and its impact will be explored further in chapter 5.

Stroker, Turbo Charger, Supercharger, and More: In recent years, availability of performance parts for both the 2.5L and 2.4L has been diminishing due to less interest in aftermarket modification of these engines. As stated earlier, there is a money line to cross for a swap to a larger engine that is more cost effective and that will produce better results. Some of the fanciest and most expensive supercharger kits and turbo kits for the 4-cylinder engines produce 170–190 hp in the stock 4.0L range.

For those willing to spend the money for the challenge of squeezing more out of their small engines, stroker engines are available that can push the engine size of a 2.5L up to 2.7L. The 2.4L engines have a bit of a larger aftermarket following due to their use in a variety of Chrysler vehicles. Once again, being conscious of cost versus benefit will save you money that may be used better elsewhere.

The stock 4.0L is almost the perfect engine for the TJ, its modern fuel injection and engine technology only adds to the reliability of this engine. Putting out approximately 190 hp and 235 ft-lbs torque, it is well matched to the size and weight of the TJ. It’s not uncommon for a well-cared-for 4.0L to last more than 250,000 miles.

4.0L MPFI I-6

The 4.0L remained rather consistent through its final nine-year run. It experienced some slight design changes and a small bump in horsepower and torque. The 1997 4.0L produced 181 hp at 4,600 rpm and 222 ft-lbs of torque. The 2001 and later produced 190 hp and 235 ft-lbs of torque.

The 4.0L was so well matched to the Jeep both on- and off-road, providing excellent torque at low engine speeds; it was a definite advantage in slow off-road driving conditions. While the 4.0 isn’t a high-horsepower engine, it is capable of providing a pleasant driving experience on the street. Combine the low-end torque with excellent reliability and you can debate the merits of an engine swap away from the 4.0.

Slight variations in the run generally brought improvements as the years ticked by. The tubular exhaust manifold, which was prone to cracking, was replaced with an improved cast version in 2000. The distributor also disappeared in 2000 and was replaced with a one-piece three-coil rail system. The Jeep’s PCM controlled the spark timing after the distributor was removed, which meant that manual adjustments were no longer possible or needed. These improvements just added to the 4.0L’s reliability.

Cold air induction systems come in many forms from several different companies. All use a similar concept of a free-flowing reusable air cleaner that is protected from engine heat by an enclosure. This enclosure brings in fresh, cooler air from the grille area or cowl. These systems usually result in a gain of a few horsepower and a little extra fuel economy.

4.0L Performance Upgrades

The trouble with modern computer-controlled engines is that the computer attempts to maintain predetermined performance characteristics even after modifications. Rewriting the programming is not technically possible but programmers and performance modules attempt to piggyback on the Jeep’s computer and alter programming along the way. Even then, gains are minimal and the cost often exceeds the reward. It is a truth that is common to many performance upgrades, so a good piece of advice is be cautious of engine performance modifications; it’s often money better spent elsewhere. That being said, I list many of the common add-ons that can make some improvement, whether it is in fuel mileage, throttle response, or power.

Clean, Less Restricted Air: A new or, even better, reusable-style air filter can improve engine performance alone. These filters allow increased airflow and improve throttle response as well as fuel mileage. K&N filters are possibly the most popular reusable, high-flow filters available. A cold air intake system (CAI) can improve engine performance further by replacing the entire air cleaner assembly with a less-restrictive system that isolates the air cleaner to allow it to receive cooler outside air rather than hot underhood air. Airaid, Volant, and K&N are some of the more popular makers of CAI systems. Most of these systems are installed with simple tools in a short amount of time.

Replacing the CAI System

1 The stock air intake system on a TJ isn’t particularly bad but improvements in the style of the filter and keeping the air pulled into the intake as cool as possible will add some horsepower and fuel efficiency. Most cold air intake (CAI) systems replace the filter box with an open element housed in an isolated box to separate the air intake from underhood heat.

2 Loosen the clamp attaching the intake tube to the box and pull the tube from the box. Remove the airbox lid and air cleaner. Remove the three internal bolts to allow removal of the factory airbox. Then remove the bolt on the passenger-side radiator bracket.

3 Pull out the PCV tube and air temperature sensor (if equipped) from the intake tube and remove the factory intake tube. With all the components removed, installation of the new components can proceed.

4 Unbolt the radiator support and install the heat shield, passing the radiator support through the rear wall of the shield. Tighten the bolts.

5 Install the intake tube to the heat shield and throttle body. Install the PCV tubing and the aFe air cleaner.

6 Make sure that all of the bolts are tightened and install the trim seal on the heat shield. The installation is now complete. Test-run the engine and check for vacuum leaks or loose connections.

Exhaust and Headers: The TJ 4.0L exhaust options are plentiful from cat-back systems to entire replacement systems that include performance pipes and low-restriction emissions-legal catalytic converters. Some of these systems give the Jeep a nicer exhaust sound and tone, as well as improve performance through less restriction.

The factory exhaust manifold on the TJ can be either a tubular-steel or a cast-iron design, depending on the model year. Some model years have manifolds that are prone to cracking; typically, these manifolds can be replaced with a direct fit high-flow header that will mate up with the stock Y-pipe tubes or aftermarket tubes. For maximum exhaust performance, replacing the entire system from the header to the catalytic converter to the muffler and the exit is recommended.

A TJ exhaust system can be broken down into three sections, from front to back: the manifold, catalytic converter section, and cat-back section. The exhaust system configuration changed a few times in the TJ era. The 1997–1999 (earlier) versions used a manifold that converged from two sets of three tubes merging into one then those two sets into one with a single large catalytic converter. From 2000 to 2006, the manifolds used a dual three-tubes-into-one design using two pre-cat converters that merged the two into one, followed by a larger converter. The later design used four oxygen sensors to measure oxygen levels before the pre-cats and after.

The TJ 4.0L used a few different manifolds through its run; some years used a tubular steel design similar to a header and others used a cast-iron design. Earlier versions used a straight 3-into-1 to 2-into-1 collector design; later versions used a 3-into-1 with dual output design. The latter used small catalytic converters right after the manifold followed by a 2-into-1 collector.

Performance exhaust systems are not cheap but often can last for the lifetime of the Jeep because most are stainless steel. If your Jeep has high mileage and is in need of replacements to the exhaust, consider a high-performance system. MagnaFlow, Borla, Flowmaster, and aFe make replacement and performance exhaust components for the TJ.

aFe Performance Exhaust Installation

If you need to replace a rear main seal or oil pan gasket, now is the time to plan for that. Removing the oil pan usually means dropping the exhaust, so you might as well do both.

This TJ has more than 193,000 miles and the check engine light is illuminated, indicating a problem with the catalyst system. Onboard diagnostic (OBD) codes can be viewed on a TJ by turning the ignition key on three times in 5 seconds. The cycle is on, off, on, off, on. The speedometer will display any code generated by the Jeep. In this case it was P0432 indicating that the catalyst system was below efficiency. The issue is likely an oxygen sensor, but the old cats are way past their useful life. The muffler is not leaking yet, but the outer shell is falling off from rust. Replacing the whole system is money well spent. A performance system from aFe was chosen; it included new catalytic converters, mandrel-bent pipes, and a free-flowing muffler all constructed of 409 stainless steel. The factory manifold is in good condition and will be retained. All four O2 sensors will be replaced as well with the system.

O2 sensors are a necessary evil in modern engines. These sensors measure the oxygen level in the exhaust gases, which allows the computer to adjust the fuel mixture to achieve optimum burn efficiency. Later-model TJs used four sensors that read O2 before and after the catalytic converters. When replacing sensors, check with a reseller to make sure the proper sensor is used because Jeep used a variety of sensors.

The TJ exhaust always crossed under the engine in some location (depending on the year) to allow the pipe to run down and eventually exit on the passenger’s side of the Jeep. The crossover was most often below the oil pan. Dropping the oil pan requires the removal of the exhaust system because of this crossover.

Before starting the project, disconnect the battery and properly support the Jeep to allow easier access from underneath. The center skid plate will need to be removed to allow access to the catalytic converter and other sections. Support the rear of the transmission/transfer case with a stand or jack. Remove the transmission mount nuts and then the six skid plate bolts. If the Jeep has an automatic transmission, you may need to deal with the transmission pan skid plate. Lower the plate and move it out of the way. It’s easiest to start removal of the old system from the rear and move forward.

1 Remove the center skid plate by supporting the rear of the transmission/transfer case, remove the mount nuts, and remove the six frame bolts. The muffler and catalytic converter are easily accessed with the center skid plate removed. This difficult-to-reach area can trap mud and trail debris that increase rust potential and wear, so use this opportunity to clean here.

2 A reciprocating saw makes removal of the old system quicker because unbolting old clamps may be almost impossible thanks to rust. Cut the pipes between the muffler and tailpipe, muffler and catalytic converter, and the catalytic converter and crossover pipe.

3 The aFe tailpipe is compared to the stock pipe. The stainless-steel construction will allow this pipe to serve the Jeep for a lifetime and the smooth mandrel bends along with the larger diameter pipe allow the exhaust to flow more freely. The hangers attach at the exact stock locations, which eases installation.

4 The aFe performance muffler, compared to a stock muffler that is rusting away. The smaller size and freer-flowing internal design adds horsepower to the Jeep along with a pleasing exhaust tone. The stainless-steel construction will likely allow this muffler to serve the Jeep for its lifetime.

The later-model TJ dual mini catalytic converters are located right after the manifold. They are equipped with a downstream O2 sensor immediately after the mini cat. The crossover pipe goes under the engine oil pan, taking the exhaust to the passenger’s side.

With the rear sections removed, the crossover and lead pipes are next to come out. These are difficult to reach and will require patience. Unplug the lower O2 sensors before removing the bolts. With the lead pipes unbolted, remove the lead pipe and crossover.

Because of this Jeep’s excess mileage, all of the O2 sensors (four in this case) will be replaced, so their removal from the old lead pipes isn’t necessary unless the sensors are to be retained. At this point, the upper O2 sensors are unplugged and removed, followed by installation of the new sensors. Access to the sensors with the lead pipes removed is much easier.

Attach the sensors back to the wiring harness. Then install the mandrel-bent section of the lead back to the main catalytic converter. Install the supplied band clamp loosely.

5 Installing the new O2 sensors is easy with the lead pipes out of the way. Each sensor should come with some installation lubricant that aids installation and prevents the sensor from seizing over time. Tighten to manufacturer’s specifications; be careful of the wiring hanging from the sensor.

6 Install the new O2 sensors in the lead pipes’ section and tighten to the manufacturer’s specifications. Raise the section in place and loosely bolt the section to the manifold with the four bolts. Observe the front driveshaft clearance and adjust to prevent rubbing.

7 Position the aFe converter in place to line up with the factory bushing hanger. The aFe directions indicate to cut the lead pipe 3.25 inches from the end when using the aFe converter. Tighten the supplied band clamp loosely.

8 Complete the installation by installing the muffler to the converter at the flange and attaching the tailpipe to the muffler using the supplied band clamp. The factory hanger locations should match up.

After everything is installed loosely, begin tightening from front to back until everything is properly tight and fitted in the hangers. Be certain to attach all of the new oxygen sensors to the factory wiring. Start the Jeep and listen underneath for leaks. After 50 to 100 miles of driving, check all bolts. In this case, the check engine light went off without interaction because the system was functioning properly. Clearing codes will vary depending on the year of the Jeep and the particular code. Some codes will clear with the battery disconnected while others require an OBDII device.

Throttle Bodies and Spacers: The 4.0 throttle body simply serves as an air regulator, unlike a traditional carburetor that regulates air and fuel. The throttle position sensor on the throttle body provides feedback to the computer to indicate the position of the throttle so that other engine systems, such as the fuel injection, are matching the engine needs of the driver. Performance throttle bodies that use a larger opening are available; they allow an increased volume of air to pass through the throttle opening, allowing more fuel to be burned, thereby increasing power. Painless makes bolt-on throttle bodies that feature a 70- and 72-mm bore as opposed to the factory 60- to 62-mm bore.

Several companies make throttle body spacers that are designed to alter the flow of the air moving into the engine, allowing increased efficiency. Airaid, Hesco, and aFe make throttle spacers that can be installed in less than one hour.

Superchargers: For those dying for more horsepower, and have money to burn, a supercharger will add a 40- to 50-percent horsepower increase and a 30- to 40-percent increase in torque. At the time of this writing, a supercharger kit for a 4.0L costs in the range of $3,000 to $5,000. That’s a lot of money to go from 190 to 270 hp. It’s likely still less expensive than a V-8 swap with much less fabrication and hassle, but the numbers aren’t as impressive as a V-8 on its own. In addition, a supercharger can be hard on an older, high-mileage engine.

Sprintex continues to make a bolt-on supercharger system for the TJ while many other companies have discontinued their systems due to the age of the TJ. The Sprintex system mounts directly to the top of the intake and relocates the throttle body, unlike many older or homemade systems that pressurize the entire intake system with a separate mounted supercharger feeding air through a tube to the throttle body.

Jeep owners have used Eaton M90 superchargers from late 1990s to early 2000s GM vehicles to create custom installations. Boosted Technologies took this practice a step further by making a true bolt-on system that uses an M90 twin-rotor design supercharger mounted to a custom adapter on the intake manifold and relocating the throttle body. The supercharger pulley is located near the power steering pump and runs off the engine’s serpentine belt.

Programmers and Performance Computer Modules: Like the 4-cylinder engines, Jeep owners can add a performance computer module or programmer to their Jeeps. These components work similarly in that they alter the original programming to allow the engine to increase power and efficiency. Modifying fuel ratio, spark timing, and other points often accomplishes this. Some modules are fully adjustable and some require high-octane fuel as well as changing engine thermostat to allow the engine to run cooler. Most modules attach to the PCM directly and can be installed in less than an hour.

Stroker: A stroker is an engine that uses a crankshaft from a different engine or a custom crankshaft to increase the stroke of the engine, resulting in increased horsepower and, more significantly, torque. For many Jeep owners, this is an attractive way of gaining some increased performance without the expense and complexity of an engine swap. A stroked engine fits in the same space and requires no adapters, fabrication, or electrical modifications, and it shouldn’t create any emissions nightmares.

A 4.0L can be commonly (safely) stroked from 4.6L to 4.7L; some have pushed the engine to a 5.0L. A common trick is installing a crankshaft and connecting rods from a 4.2L (258 ci) into a 4.0L and increasing the bore up to .060 inch. This method almost “squares” the engine, meaning that the bore and stroke are almost identical. Some builders will use the 4.0L connecting rods and special pistons to further increase low-end torque, but this method is often more costly and uses non-stock pistons. The horsepower and torque differences between using the long or short rods is likely trivial. An off-road Jeep will benefit from the added cubic inches in either way.

It is common to include an array of performance parts in a stroker engine. Keith Black pistons are a popular high-performance piston, as are performance camshafts from Elgin or Crane. Several camshaft duration/lift options are available to suit the need of the application. Edelbrock makes an emissions-legal performance aluminum head for the 4.0 that increases and improves flow in both the intake and exhaust ports. It should be noted that the Edelbrock Performer head will work with the 1997–2006 TJ 4.0L, but a 1997–1998 exhaust manifold or headers must be used. In addition to the internals, higher-output fuel injectors are often included.

The 4.0L can be stroked to increase displacement up to 4.8, often using a crankshaft from a 4.2L along with bored cylinders. Several companies, including Hesco, ATK, and Clegg, make stroker kits as well as fully assembled engines that are ready to install. (Photo Courtesy Titan Engines)

A stroked 4.0L combined with a free-flowing exhaust, larger throttle body, higher-output injectors, and cold air intake may be the ultimate I-6 combination without the hassle or expense that comes from an engine swap. It is common to see gains of 40 to 50 hp and 60 to 80 ft-lbs of torque. Building a stroker at home is no small task, and it is probably best left to those with engine-building experience. Golen Engines, Titan, and Hesco make full and partial 4.0L stroker kits for the TJ.

Cooling: Keeping the engine cool, especially on the trail where the Jeep is likely maintaining a slow speed for extended times, can put stress on the system. In general, a 4.0L, even with the stock cooling system, is very capable of maintaining proper engine temperature even on the hottest days on the trail. Over time, if this system is neglected its capacity is diminished and overheating problems, which are bad in general but worse on the trail, may appear. Performance upgrades, primarily internal engine mods, will increase the amount of heat that the engine generates, which increases the load on the cooling system. In short, this is not a common condition in a Jeep with a 4.0L. Regular flushing, inspection, and (especially) keeping the radiator fins clean will make this system perform at its optimum level.

Direct-fit aluminum radiators can do a better job of displacing engine heat than the factory radiator. These radiators usually use more cores and full-aluminum tanks. Many aluminum conversion radiators are used for swaps that are direct fit to the Jeep to match the engine.

Hood vents are extremely useful for reducing underhood temperatures. Some Jeep owners install vent kits or purchase aftermarket hoods with integrated vents. A Jeep that experiences slow off-road conditions in hot environments will benefit from a vented hood.

Gearing: If you don’t go to a full-on engine build, such as a stroker, changing gears can have a dramatic impact on the Jeep’s performance by getting the engine back to its designed power range. Adding larger, heavier tires will effectively alter gear ratios, causing a reduction in engine RPM at the same speed. Performance and fuel mileage will suffer if the engine falls too far below its designed power range.

The 4.0L is a well-known low-RPM-torque engine that will operate in the 2,000-rpm range at 65 mph. Finding the proper gearing to keep the engine at peak RPM will enhance both performance and fuel mileage and that will make the driving experience better. Gearing and ratio choices are discussed in chapter 5.

Swapping Engines

Swapping engines in Jeeps is common and has been performed countless times, stretching all the way back to the earliest CJs. For many Jeep people, it seems impossible to satisfy the hunger for more power. As time moved on, engines became increasingly sophisticated and complex, mostly to improve vehicle emissions and improve fuel mileage. There was a time in the mid- to late 1980s when swapping engines became almost impossible, especially when the Jeep needed to pass an emissions test.

Luckily, the aftermarket caught up to the times and began offering components to make swapping a modern engine into a TJ easier than ever. We are in good times now. Modern engines make more power than ever, maintain fuel economy, and stay within required emissions standards.

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 of horsepower and torque. In fact, too much of either can lead to broken components and poor fuel economy. This Jeep is being built for slow trail running and off-road conditions that will make better use of low gearing and low-RPM torque rather than high horsepower.

Because the 4.0L engine performs so well in a TJ right out of the box, spending extra money for improving performance should be considered after items that make a bigger difference off-road are installed first. A quality CAI system and a performance exhaust system will give the largest improvement in the TJ 4.0L; these items may be the first of the modifications a Jeep owner may do.

The 4.0L is a well-matched engine for the TJ and serves the Jeep well in almost all driving situations. There was much fear in the Jeep community when Chrysler announced it was being discontinued and replaced with a new engine in the new JK model. Adding a few performance modifications, watching gearing, and performing proper maintenance will allow this engine to power a Jeep for years.

Swapping a 4.0L in place of a 4-cylinder engine is not terribly complicated and can be done at a reasonable cost for a significant improvement. Having access to the donor Jeep will reduce the expense and complexity of the swap.

Retaining an already-installed 4.0L is more cost effective. It also eliminates the almost endless potential for problems, including adapters, fitment, exhaust, emissions, and electronics compatibility.

V-8 and other non-factory swaps should be performed in accordance with your local emissions laws. A modern, fuel-injected engine with all of its necessary components will perform best in a TJ. The GM V-8 is one of the simplest and most-developed engines swapped for a TJ engine. Planning and preparation are the keys to a successful swap.