Ford Windsor V8 power is actually a very good choice for the YJ Wrangler. These engines develop great power and they fit well into the envelope of the Jeep's engine bay.
This won't be much of a comparative discussion between GM and Ford V8's, but our customers do often ask us our opinions on the topic. Ford V8's are smart swaps, especially if using a Ford manual transmission or the Jeep AX15 transmission. When considering an automatic, the GM lineup does provide greater options. Fuel injected Ford V8's are especially exciting for a Jeep engine swap. A 5.0L in their various tunes will offer great performance and a 351 EFI even more so. Ford engines are light, narrow and have the distributor favorably located. These engines are a bit longer than Chevy V8's, but they can nest deeper into the firewall area to compensate for this, leaving adequate room for cooling components.
These conversions take some basic planning and effort in their execution, but the results can be quite fantastic. With improvements in power, fuel economy, reliability and broad range driveability, once one has driven a YJ with a proper Ford conversion, it is tough to ever look back.
Before we talk procedure, let's cover a bit of the history of these Jeeps and their key parts that will play a role in the planning of a successful conversion.
The YJ underwent many significant changes from its CJ predecessor. The legally embattled AMC, having been grilled for the hyped rollover risks of the CJ, specified a 6" wider track for this new generation of truck. This entailed a wider frame and a somewhat refined suspension, featuring wider and longer springs and an anti sway bar that together provided a set of road manners not yet seen by its preceding generations.
The YJ did retain the same body width wheelbase length specification as the CJ7, at 93.5". However, the frame was formed of a heavier gauge steel and stronger throughout its length than all prior CJ Jeeps. This 1987 YJ was introduced with a standard, painted steel body, but for 1988, Chrysler specified and produced the body in galvanized steel, greatly adding to the rust resistance of this new model.
The styling of the front clip was arguably less graceful than the CJ. The headlamps and signal lights were squared as were the fenders and even grille slat openings. The boxier design trends of the mid-eighties had their way with the new Wrangler, and made them the butt of jokes from a generation or two of die-hard CJ buffs. But the jokes began to fade as a classic breed of off-roaders began to turn these YJ's into increasingly commendable trail rigs.
The YJ was released with two available engines; one being the AMC 2.5L, four-cylinder with 105 hp. This was AMC's newly designed and released engine, whereas they had used the GM 151 Iron Duke four-cylinder in previous Jeeps. This improved MPI four-cylinder persisted and increased slightly in power through the 1995 model year.
The AMC 258 I6 was carried over from the CJ line, and still in carbureted form. It's ever increasing entanglement of emissions control complications were no help. This engine persisted through 1990 and in 1991, an upgrade to the 4.0L I6 made its way under the hood. No doubt an improvement, the 4.0L was a welcome change but hardly anything to write home about. This 4.0 had made it into the Wrangler late enough to get the Mopar engine management system, bypassing the Renix system as found in the XJ from 1987-1990. Power was up and fuel economy nudged up a bit from the 258, and the addition of this engine boosted the YJ powertrain into a somewhat more respectable realm. Claimed fuel economy for the best rendition of the YJ 4.0L I6 was 15 city/18 highway MPG, though people consistently report less than this.
The stock manual transmissions in the six-cylinder versions of these Jeeps included firstly the Peugeot BA10/5 five-speed, from 1987 through mid-1988. This transmission was the unfortunate result AMC specifying a gearbox made by a company arguably out of touch with the torque demands of a truck and off-road vehicle. It is nearly famous in Jeep circles for its weaknesses. Adapting any decent engine to this transmission is futile and we offer no adapter to do so.
As a middle model year change in 1988, the six-cylinder YJ received the AX15 five-speed transmission. This transmission was a clear improvement over the BA10/5 and as such, remained as the standard shift transmission in the six-cylinder Wrangler through 1999.
The AX5 five-speed manual transmission was standard with the 2.5L four-cylinder engine throughout the span of the YJ's production. This transmission is light-duty. They are known to fail even behind the anemic 2.5 I4. We neither recommend nor make any conversion to retain this transmission.
The automatic transmission available with the 2.5L through 1991 was the Torqueflite TF904. This transmission has a better history than the AX5, but we still recommend replacing it when upgrading to any motor that is significantly stronger. The 30RH automatic came with the four-cylinder from 1992-1995. All of these gearboxes that were available with the 2.5L are rated and proven as light-duty.
Automatics for the six-cylinder YJ were primarily the TF999, followed by its variant, the 32RH. These transmissions are adequate, but nothing to get too excited about.
Jeep has usually excelled in its transfer case offerings. This remains true with both models of transfer case offered in the Jeep Wrangler. With the intro of the YJ, we saw the first chain-driven transfer case in the Universal lineup. The aluminum cased, driver's-drop gearbox was there to stay. The 1987-mid 1988 Jeep YJ featured the part-time four-wheel-drive NP207 transfer case, as made by New Process Gear.
In mid-1988, the YJ was upgraded to the New Process NP231J (also called the NP-231 or the New Venture Gear NVG 231) part-time transfer case. This transfer case was the de facto reliable transfer case with all four and six-cylinder YJ's through the remainder of their production span.
Both transfer cases appear to be similar. If you own a 1988 YJ, you can easily identify which model you have by reading the red and silver tag on the rear half of the case. We encourage your additional reading about your transfer case, by following the above links.
It is crucial to discuss transmissions early on. They are sometimes more central to the conversion than the engine.
In the entire production run of the YJ Jeep, all transmissions except one should be ruled out when performing a GM engine swap. These include the AX5, Peugeot and 904 / 30RH transmissions, which were hardly durable behind the lackluster factory engines. Ford power can spell their demise within days to weeks. The AX15 manual transmission, however, can be successfully retained in a Ford engine conversion. Details, below.
Though some of these following transmissions do not offer overdrive, many Wranglers with larger tire sizes and proper axle ratios will still allow for a respectable freeway cruising RPM. An individual is best to perform some gearing calculations as part of this stage of the planning.
Auto trans options for Fords in Jeeps are just not great. The C6 is too long, the AOD is alright but year to year changes stifle adapter developments and requests for C4 swaps into these Jeeps are rare.
The predominant portion of YJ's were equipped with manual transmissions with the remainder featuring automatics. If converting from automatic to manual in conjunction with your engine swap, note that the installation of the OEM clutch pedal, master cylinder and related components is not difficult as the provisions to do so are already in place.
Many Jeeps are destined for more hybrid or even hard trail use and some individuals will be choosing manual shift, heavy-duty truck four speeds to place behind their Ford powerplants.
Ford T18: A choice, heavy duty, four-speed transmission for the Ford & Jeep enthusiasts alike.
• The NP207 & NP231 transfer cases are adaptable to the T18 by using our #181 series adapter kits.
Ford NP435: Also held in high regard for Ford conversions is the New Process 435.
• The NP207 & NP231 transfer cases are adaptable to the NP435 by using our #431 series adapter kits.
AX15: If your Jeep happens to have the AX15 five-speed transmission, you may choose to retain with your Ford engine conversion. Though perhaps not suited for wild V8 power or punishing off-roading, mild V8's and V6's and all around trail use make the AX15 good match. Adaptability is not difficult, and is accommodated by our #FMAX series adapter assemblies with the use of your existing Ford "Butterfly" style bellhousing. This transmission's overdrive feature can be useful for Jeeps with moderate tires and general hybrid usage.
Options outside of these mentioned are usually not practical, useful, affordable or any combination of the three.
The NP231 transfer case is strong, versatile and your YJ likely already has one.
Most of the stock transfer cases found in these Wranglers are durable and quite appropriate for V8 power. The NP207 has its fans and detractors. Many of our customers choose to replace it with the Jeep NP231.
This is where the planning gets most interesting and the decisions most subjective. The very first decision to be made here involves this: what kind of power do you need to do what you want with your YJ? From 289 up through 351 and from simple carburetor and ignition systems up through a full OBD-II compatible 5.7L; the choice is yours based on your comfort level.
A Ford 302 / 5.0L rear sump oil pan, available affordably from Ford Racing Parts (#M-6675-A50).
A Ford 351 / 5.7L rear sump oil pan, available affordably from Ford Racing Parts (#M-6675-A58).
The oil pan sump location should be considered when choosing any of these Ford V8 engines. Most of them have front sumps that cause front differential clearance problems. The 289 and 302 engines can be fitted with a rear sump oil pan and pump pickup from a Bronco or ‘83-‘93 Mustang 5.0 engine. We've also heard from our customers that the oil pan off later model Explorers with the 5.0 has the correct pan configuration.
There are two completely different block bolt patterns used on the Ford small block V8s. The first small blocks were the 260 cubic inch engines in 1962-64 and the 289 c.i. in 1963-65. These engines are usually referred to as "5-bolt" engines because they had five bolts attaching the bellhousing to the block. 5-bolt engines have a transmission bolt pattern that measures about 6-1/4" wide by 7-1/2" tall and have a 4.687" bore in the bellhousing.
Some 1965 and all 1966 and later 289, 302, and 351 Ford V8s are referred to as "6-bolt" engines because of the six bellhousing to block attaching bolts. These 6-bolt engines have a transmission bolt pattern that measures about 8-1/2" wide by 6-5/16" tall with a bore diameter of 4.850".
The modern incarnations of these motors are very good. Fuel injection versions through 1995 are good to work with and readily available. OBDII versions (post-'95) promise to be more difficult to work with due to computer and electrical issues.
This question has been at the forefront of the conversion world for a while now. There is something great about a simple, clean, unencumbered carburetor and simple ignition system. However, there is something excellent about a modern, self-adjusting, efficient, operate-at-any-camber fuel and spark delivery system.
No doubt that many individuals are in their comfort zone with the earlier hardware, but distill it down to the basics and it is the same essential thing that was going on in 1903; getting fuel and spark into the cylinders with the right mix and timing. There is no way around the conclusion that fuel injection systems do this better and in a broader range of conditions. Old iron is really cool, but this author has lived squarely during both carbureted and injected eras, an I see fewer breakdowns than ever, and have been in the bays and at the wheels of enough injected vehicles to know that they use less fuel to generate more power and in a cleaner, more reliable manner than their predecessors.
We get an occasional call from customers that have found a great V8 and ask if they can put a "simpler" carburetor on it. This has every distinct disadvantage that we can think of: increased parts cost, decreased efficiency, driveability and reliability. Don't even think about it. Fuel injection is generally much easier to work with than too many people think.
That being said, choose what you want. Unless, of course, you have emissions restrictions...
Not just for Californians anymore, vehicle emissions considerations play a big role for most swaps. However, we feel that the fear of emissions by swappers is very overblown. It simply is not the challenge that many perceive.
Back to Californians; if you can pass California emissions standards, you can pass almost* any state or county regulations. As such, we will focus on the way the California Air Resources Board does it.
We’ve read that California law does exempt 1973 and earlier vehicles from emissions regulations. The CARB web site, however, mentions that vehicles since 1967 are not exempted. Again, do your research. Of course, based on the target of this manual, most conversions in question will be in later model Jeeps.
Engine conversions, according to California regulations, are to meet the following standards:
“Engine changes are legal as long as the following requirements are met to ensure that the change does not increase pollution from the vehicle:
After an engine change, vehicles must first be inspected by a state referee station. The vehicle will be inspected to ensure that all the equipment required is in place, and the vehicle will be emissions tested subject to the specifications of the installed engine.
Note that there are two emission systems to consider: Exhaust and Evaporative. The former consists of burning (and reburning) the fuel and air to the cleanest state possible, and then reburning yet again through the catalytic converter in the exhaust circuit. Evaporative emissions consist of how the unburned fuel is stored and transferred in the vehicle. The principal piece of hardware used here is a charcoal canister that absorbs fuel fumes as they slowly evaporate from the tank and lines. Upon starting the engine, the canister is purged of these fumes through engine vacuum and the temporary opening of a purge valve. Usually, one should retain the Jeep's existing canister as it already fits, and evaporative emissions management are no different for the engines involved.
Your Jeep is considered to be a “Light Truck” by most jurisdictions. As such, you can usually source your engine from a Ford truck or SUV without failing your emissions certification. However, this again is according to local laws and your research is encouraged. Car engines do burn cleaner and may be more affordable as well.
There is simple and specific strategy to pulling an engine or engine/transmission combo from the salvage donor vehicle for the best results for your Jeep conversion.
You need four or five key things:
This is usually how the engine is shipped by the pros and it is salvage industry standard to include the above, with the exception of the accessories in some situations.
One of the most interesting questions we've gotten over our company's 37 years is this one: "Will you (or your instructions) tell me exactly where to put my engine into my Jeep?"
Our answer to this, in a word, is, "no." You're probably intelligent enough to own a Jeep, surely clever enough to find and read this article, possibly brave enough to plan and perform the conversion... trust us when we tell you that you will know where your new engine needs to be placed within your engine bay. Placement is not hard, and it is actually a very satisfying part of the project - to decide the optimal location of the powerplant.
The placement process works by top-down engineering. This consists of loading the engine with all of its accessories, including the exhaust manifolds. Lower this assembly into the engine bay and start nudging it around. You are looking for:
Our experience shows that the Ford engine will come ahead about 2" from the stock I6 location in most situations.
Removal of the stock frame brackets is required to make way for the new engine. We recommend our #MMX-NF1 mounts for Ford Small Block V8 engines. They make for a clean, strong installation, and their versatile adjustability makes them ideal for a variety of conversion options. They are typically welded on to the Jeep frame for the best results. The Ford motor mounts manufactured by Novak (shown) are installed on the engine to replace the original Ford cushions. These brackets completely replace the original Ford mounts. The gusseted frame brackets weld to the inside faces of the frame rails and support the weight of the engine through the neoprene insulator. The other insulator fits under the frame bracket to effectively dampen engine vibrations without being too soft. Refer to our instructions supplied with motor mounts for more information.
It will be little news to most readers that the factory radiator will not work with a conversion engine both in terms of cooling capacity and outlet location. Novak started swapping V8 engines into YJ Jeeps several years ago and setting up a cooling system was a challenge. Since then we now offer a bolt-in performance aluminum radiator with the outlets already configured for Ford power. See our Cooling Components section to view the line-up.
As engine choices vary, you will need to choose your hoses from amongst those on hand at your local parts source, whose length and curves are based off wire bent templates you can fashion.
Using a Novak RadLock radiator, a Novak customer documented the use of Gates hose #21941 for the upper inlet, trimmed some at each end for length and diameter. For the lower, a Gates #20957 was trimmed at one end for the length.
We are unaware of any OEM radiators that will work without some extensive modifications. Additionally, the narrow grille of the Jeep calls for an aluminum radiator that dissipates heat faster than the copper / bronze versions.
This cable pass-through speed sensor (VSS), by Dakota Digital (#01-4160) will feed an appropriate speed signal to most Ford PCM's, for fully appropriate functioning and fuel delivery at all speeds. It will connect to your Dana 20 speedometer gear output.
Some view the electrical and wiring aspects of a conversion as the 800 lb. gorilla of the swap. In fact, it is seldom as difficult as perceived.
At the most fundamental level, whether you are working with a carbureted, throttle body injected or multi-point ("tuned port") injected engine, you will retain and connect the original Ford alternator in the same manner as was the Jeep alternator; the same for the distributor, etc.
From basic (TBI) to advanced (TPI) injection systems, the swaps are still largely the same.
For fuel injected swaps, you should know that the engine and its PCM are largely self-supporting. In other words, the very grand majority of the engine wiring harness goes to (sensor data) or comes from (systems control) the PCM, and most sensors are directly related to the engine itself. If uninstalled correctly, most of this harness will be intact and not needing any splicing. Like any electrical item, the computer needs power and ground, and a power distribution center (largely consisting of relays and bridges - you can keep the Jeep one!) to switch and of course, distribute power to the various systems.
The installer should keep one simple principle in mind: make the engine think it is running in its original Ford chassis. A simplistic but fair summary would state that a 1968 Ford 302 and a 1992 5.0L have the same basic wiring requirements; power to the starter when it is required, power to the distributor (or coils) when needed. The battery needs power from the alternator to keep it charged.
Installers will be pleased to hear that steering need change none or very little to perform the engine conversion. You will use a Ford power steering pump and its bracketry that is usually native to the engine being installed. Not all brackets place the pump in the most friendly position vis a vis the steering shaft, so be aware of factory or aftermarket alternatives that will better place the pump for your swap.
You will retain the factory Jeep power steering gear. You may need the assistance of a hydraulic shop to have the high pressure (feed) hose ends matched or adapted as per your pump and gear combo. Usually the low pressure (return) line can be cut from hose stock and secured with the use of hose clamps.
Customer Tom Uhl shows a sanitary install of a Ford 5.0 V8 into his CJ. The reader may notice that the front accessory package is hardly short, but there is still the room needed for a clean swap, requiring no more room than the I6 and with much better power and reliability.
You'll be replacing one of three factory engines. Their nominal estimated, accessory loaded weights are:
Engines you may replace these with may include:
Factory springs are usually great for most Small Block V8 engines. We have replaced four-cylinder Jeep engines with V8's and noticed no sag or overly soft ride in the front axle. Aftermarket springs usually make no distinction and are rated well for most engines this side of Big Blocks.
Lift is not required for the Jeep to perform the engine swap, but may be done for reasons external to the swap.
Fuel pumps have evolved from low pressure (4-12 PSI) mechanical, engine mounted units for carburetors - good at pulling fuel over a distance - to medium pressure (13-18 PSI), electric in-tank pumps for throttle body engines, to high pressure, electric, in-tank pumps. These latter pumps are designed to push fuel, not pull it, and at pressures ranging from 38-50 PSI for multi-point injections systems.
Additionally, with the higher temperatures that these high-pressure pumps generate, their immersion into the cooler fuel is critical for the durability of it's electric motor. External pumps of the same ratings are available and are self-cooled by being built into heat dissipating aluminum housings.
Earlier Jeeps that have fuel tanks that were set up for carbureted engines may provide some problems, especially in off-road environments. Fuel injected engines require an uninterrupted supply of fuel, and baffles built into an injected style tank keeps the fuel from sloshing out of the intake of the pump. Carbureted setups don’t have this concern due to the built-in fuel reservoir the carburetor that provides for any gaps or air-pockets in the flow.
If you are working on a pre-injection Jeep, consider buying an aftermarket fuel cell, or having an inline reservoir made to buffer any interruptions in the fuel flow to your injectors. Or, install an external fuel pump and mini-reservoir at the closest point to the fuel tank that is available.
Some engines will require more pressure and will therefore need a new pump, either in-tank or auxiliary. Some engines will require less pressure, and an in-line restrictor may be your key. Various fuel pump and restrictor systems are available on the performance parts aftermarket, and, as mentioned earlier, you may wish to have your fuel tank modified by a professional to accept a different pump. Aftermarket fuel cells also provide a flexible solution to some of these problems.
Narrow, blockhugging style headers make fitment much easier than with most factory manifolds, and allow the Ford V8 to breathe easier.
No doubt that getting exhaust air out of the engine is a more elaborate process than getting combustible air in.
The installer must run a header that is tight fitting. The shorty, block-hugging style is the best bet. You can find these headers, here.
Garner the services of a local exhaust shop to help you put together a clean, safe, easy flowing exhaust system and one in accordance with your local regulations. If you are running a TBI, TPI or Gen. III+ engine, you will also need to have O2 (oxygen) sensor bungs - typically one per bank - welded into the down pipes below the headers. California installations will need to utilize a header that is CARB certified.
While the YJ has a relatively narrow window in which to run pipes, and a transfer case to dodge as well, you can run dual exhaust. However, we suggest running the driver's side exhaust circuit under the rear wall of the oil pan and in front of the transmission / bellhousing face, into a Y-pipe joining it with the passenger side circuit. You can also run this Y behind the transfer case (give yourself some room to service the transfer case later) and then into the exit circuit. From there, run rearward to the catalytic converter and then the muffler, following which, you will arc the last section of pipe up over the rear axle and then straight out the back with the tailpipe. 2-1/2" diameter pipe is usually very adequate and will flow as much as you need. 3" is an option.
This is one way to run the exhaust circuit. You may also run the cross-circuit under the bellhousing. Work closely with your exhaust specialist in coming up with a system that will not detract from the serviceability of other parts under your Jeep, and maintain heat, ground and other working clearances
Leave the factory heat shielding in its location and position your catalytic converter and muffler under it.
Muffler choice is up to you, and possibly your passengers, neighbors and local noise ordinances.
Another inordinate concern too many people have is about driveshafts. This is not a significant challenge, especially if you are using our compact adapter assemblies with the transmissions suggested above.
Most factory transmission and adapter combinations to the 207 / 231 transfer cases vary. As such, it is often that driveshaft lengths will need to be changed to accommodate the swap. Also, consider that there multiple ways to install a conversion engine and the following will be of note:
It is seldom a good idea to allow the driveshafts to make the decisions as to where the powertrain will be placed. Some of our customers, fearful at the perceived expense of new or modified driveshafts, attempt to let the existing driveshafts dictate engine, transmission and transfer case location, sometimes to the detriment of the project. Driveshaft modifications are usually inexpensive when performed by driveline, RV or tractor implement specialists. New driveshafts are an option but seldom a requirement in regards to the actual successful conversion. Jeeps that require extensive travel or specialty-built driveshafts have this option available through several fabricators across the nation.
This popular rear mount is strong and easy to set up with any Jeep swap. See our lineup of rear mounts, here.
There are only three major places a powertrain needs support and mounting. Two at the engine, and one under the rear of the transmission (some transfer cases have the provision for a side mount to help control torque kick-back). Nearly all Novak adapters have cast-in or modular mounting bases that are configured for use with an industry standard urethane rear mount.
There is no need whatsoever, in terms of the engine & transmission swap, to use a different crossmember than the factory versions. They are typically low profile and can easily be predrilled for a new transmission mount unit. Unless you are retaining a AX15, getting rid of the factory urethane mount and any ancillary bracketry with it is the largest favor you will do for yourself in this area. Go with a clean, simple, industry standard mount like the Novak #RMU. You may need some simple spacers. Box steel or aluminum pucks are useful here. Anything needing to be fabricated needn't be elaborate.
Many people mistakenly think that a more powerful engine demands stronger-than-stock axles. This is not necessarily the case. The factory Dana 35 and Dana 44 rear axles (the latter usually being found on towing package option Jeeps) can withstand very ambitious engines. Such is the case for the front Dana 30 as well. Whether your converted Jeep needs stronger axles is more a question of how you use them, and usually in terms of off-road considerations more than on-road use.
Axles are generally out of the scope of our work here at Novak, but there are plenty of companies that deal with them to be of assistance if you feel you must upgrade them as part of your conversion.
A very clean way to ease the linkage installation process in terms of the transfer case is to use Novak's innovative #SK2X assembly. Read about it here.
This topic generally covers throttle, clutch release and transmission & transfer case shifter systems. As with many aspects of a swap, this can be a simple as the installer would like it to be.
Nearly all modern Jeeps and Ford engines use sheathed cable for throttle control. You can use the Jeep throttle cable against the Ford carburetor or throttle body.
Transmission and transfer case shifters are discussed in instructive detail in the Novak instruction packages that will come with your gearbox adapter assembly, and specifically to your particular drivetrain choice for your Jeep.
A stronger engine means faster acceleration and sometimes the ability to tow, as the YJ's chassis is rated to tow up to 2,500 lbs. However, the ability of the Jeep's brakes to bring things to a safe halt may be below what it should be.
As a general rule, if the brakes were good before the swap, they will probably adequate after the swap. However, many YJ's, especially those prior to 1990, had weak brakes from the factory. It is up to the individual doing the conversion to ascertain whether or not to upgrade the braking system. Brake systems are out of Novak's scope, but there are companies and shops that deal with brake upgrades, usually involving larger discs & drums, four-wheel discs, occasional master cylinder upgrades, etc.
This article is meant to be introductory and to give the reader an idea of the scope of a conversion project. No two swap combinations are ever exactly the same, but an understanding of the principles and parts involved will take any thoughtful installer a long ways. As discussed in this guide, further and more deeply detailed information comes with Novak adapter assemblies, engine mounts, radiators and other components. Additionally, our customers can speak with our Techs about the conversion being performed.
All in all, there is no change to your Jeep that is more exciting or beneficial than a powertrain conversion. Individuals have been swapping Ford power into Jeeps for decades and they still occur with frequency and great success.