The Full Size Jeeps (FSJ's) are among the most noble and impressive the the Jeep vehicles, and they have become some of the most sought after and treasured Jeeps of all.
The following article is the culmination of the summary of knowledge that Novak and its customers have gained over decades of successful swaps. Included is the information needed to plan for a great and most affordable process. However, 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 FSJ is among the simplest and most accommodating Jeep platforms for a powertrain conversion. As the reader is probably aware, the Wagoneers and J Trucks (aka, Gladiators) changed very little in form and structure from their lifespan of 1962 - 1991, and as such, we've written this article to cover conversions and their particulars for this entire span.
One of the primary goals here is that individuals have the information to choose smart, sanitary solutions that require a very minimum of invasive, unattractive or unreliable conversion work.
We recommend the following engines as top choices:
GM engine conversions into these Jeeps are fantastic. These swaps are exciting, enjoyable, beneficial and well-documented as with these Jeeps. Individuals are swapping for reasons as varied as the uses of the Jeeps themselves, and the results are invariably among the greatest of improvements owners will make. The move to a cleaner, stronger, reliable, efficient, serviceable GM engine is one that makes its own good case.
The Jeep FSJ's featured the very widest variety of transmissions:
Jeep has usually excelled in its transfer cases. The Dana Spicer Model 20 was the most common transfer case in all of these models of Jeep from 1962-1979.
The FSJ Jeeps were the first to use the Borg-Warner Quadratrac transfer case in 1973. It was used through 1979.
In 1980, the Jeeps were reconfigured and moved entirely to New Process transfer cases, including the NP208, NP219 and NP229.
More on transfer cases in a minute...
It is crucial to discuss transmissions early on. They are sometimes more central to the conversion than the engine.
Though some of these following transmissions do not offer overdrive, many Jeeps 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.
Every transmission we recommend on our website is available to the FSJ Jeeps. Length is not an issue here.
No adapters are generally needed to marry the following GM automatic transmissions to their usually matching Chevrolet or BOPC engines.
TH350: Swappers may consider the GM TH350 automatic. The Turbo 350 is strong, compact, widely available and affordable to buy, service and build.
TH400: In the no-holds-barred strength category, the TH400 may be the obvious automatic of choice. The Turbo 400 can be a good option.
For the AMC TH400 during these years does not have a case which is compatible with the GM engines. If you're wanting an automatic, changing to a different version is recommended.
700R4: This famous GM automatic overdrive is an option with Chevrolet engines and probably the most popular transmission swap for the FSJ.
4L60-E: The modern and most refined version of the 700R4 is the 4L60E, and is a great candidate as well, especially when installed with a Gen. III+ GM engine and PCM (Powertrain Control Module).
This shows the freshly painted engine bay on a Novak FSJ conversion where all the unnecessary holes were filled with epoxy or fiberglass. The transmission is in place and the mounts are welded in, enameled and ready for the engine.
It is possible to adapt the factory, AMC style TH400 (1974-1979) and the factory, AMC style TF727 transmission to Chevrolet Gen. I-II and GM Gen. III+ engines using Novak's #374 series adapter assemblies. These block style plate adapters come with a flexplate as appropriate for your engine and the associated hardware.
In our experience, these conversions can retain their automatic transmissions and transfer cases in the factory location, and the factory shifter linkages can remain the same.
The following factory and retrofit transmissions are possible options to consider:
T90: If your Jeep has the T90, it can be adapted to a GM powerplant. It is a fairly strong transmission, but be cognisant that these trucks are heavier and increased V8 power can strain the T90, depending on your usage.
• Adaptability is acheived with our #C Series adapter assembly
If your Jeep is going to require more strength and deeper gearing, consider the truck four-speeds below.
T15: If your Jeep has the T15 three-speed, it is a good, strong option.
Jeep T98 : If your Jeep has the T98 four-speed, it is a great option. It is suited for all engines and all service levels.
Jeep T18 : If your Jeep has the T18 four-speed, it is a great option. It is suited for all engines and all service levels.
Many FSJ's 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 GM powerplants.
SM420: For the old-school, ultra low geared crowd, the SM420 four-speed manual transmission is a great choice. Surprisingly well behaved on-road and absolutely burley off-road, the SM420 is a cool box of gears. If you think a transmission designed in the 1940's is an anachronism, you are right, and a very neat one at that.
SM465: Newer and a bit more refined than the SM420 is the SM465, for an only slightly less low geared transmission. They are easy to find and work with.
AX15: This reasonably strong five-speed transmission may be worth installing into your FSJ. Adaptability of the AX15 to your GM engine is very good, and is accommodated by our #GMAX series adapter assembly.
Options outside of these mentioned are usually not practical, useful, affordable or any combination of the three.
The Dana 20 is among the greatest transfer cases of all time
The stock Dana 20 transfer case found in these Jeeps is very appropriate for V6 and V8 power, and is adaptable to all of the best transmissions, as listed above. Its strength, quiet operation, compactness and longevity are a few of its virtues. The Dana 20 spanned from 1962-1979.
The next transfer case to be used in the FSJ Jeeps was the groundbreaking Borg-Warner QuadraTrac, from 1973-1979. This chain-driven, planetary reduction style gearbox was tough, but required attention to its quirks. Many individuals upgrading their powertrains use the Jeep Dana 18 as a strong, gear-driven replacement to the QuadraTrac, as it features the same front and rear axle offsets as found in these QT equipped Jeeps. The Dana 18 is adaptable to all the great gearboxes and further research is encouraged if you think this may be a good solution.
The last era of the FSJ Jeeps featured the New Process 208, 219 and 229 transfer cases. Generally, these are tough gearboxes and many retain them when doing a conversion.
Many opt to replace their OE New Process transfer cases with the later and more refined NP231 (with HD output shaft) or NP242 transfer cases, providing quiet, efficient operation and better servicability.
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 Jeep?
Now, a precursor to the rest of this section: If you got past the title of this article and are hell-bent on a non-GM engine, know that conversions this important are not walks in the park and GM engine swaps are almost invariably easier, more productive and more affordable than Dodge, Ford and other conversions. These companies make some great engines, but you have to pick your battles when doing a swap and going with a well supported, well documented, easily acquired and broadly familiar powertrain is a key to success and satisfaction.
Novak's Gen III+ engine mounts, bolted on using the factory in-frame tube spacers. The mounts feature a tab on the top that we recommend welding to the top of the frame rail for maximum strength.
Well. The sky is the limit with the FSJ Jeeps. However, economy and sensibility may be considerations here. Just be aware that nearly any of the great GM engines fit well into these Jeeps. The Vortec V6 is an option, especially the later versions whose torque and horsepower numbers put a few V8's to shame. However, do consider that these are heaver trucks and need a bit of motive power.
Our favorite considerations for this Jeep include:
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 beautiful Vortec 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 (especially GM fuel injection) is much easier to work with than too many people think.
That being said, choose what you want. Unless, of course, you have emissions restrictions...
Most of these Jeeps in most jurisdictions will fall out of emissions considerations. However, the following is listed if pertinent to your situation.
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.
Your Jeep is considered to be a “Light Truck” by most jurisdictions. As such, you can usually source your engine from a GM truck, SUV or car without failing your emissions certification. However, this again is according to local laws and your research is encouraged. Car engines may 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.
A Novak customer's Vortec V6 engine cleanly extracted and ready for installation. The wiring harness is complete and ready to plug into the computer.
One of the most interesting questions we've gotten over our company's 40 years is this one: "Will you (or your instructions) tell me exactly where to put my engine into my Jeep?"
If you are installing a GM Generation III+ V8 in a 1971-1991 FSJ, then yes: our bolt-in mountswill determine your engine location.
If you are installing a Generation I-II Chevy engine, 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:
Power steering (discussed more below) is literally as easy as connecting the GM-native hydraulic pump on your motor into your Jeep's Saginaw power steering box. Hydraulic hoses may need to be customized at your local source.
Novak's KryoFlow radiator for FSJ Jeeps and GM Gen. III+ engines is ideal. If you are using a classic Chevy V8, we use this same radiator in conjunction with a swivel-neck thermostat housing. These radiators are for later FSJ Jeeps. Gladiator style FSJ's require a slightly customized radiator, in which event we recommend you contact us for guidance and provisioning.
We recommend strongly that the reader take a few minutes and read the principles of cooling a Jeep
GM engines, especially the Gen. III+ versions run efficiently and therefore don't have excessive cooling requirements. But, to be safe, Novak's offers our KryoFlow cross-flow, double-pass radiator in an FSJ Jeep, complete with vented shroud and an aggressive but relatively quiet cooling fan. The generous cooling area provided by Jeep for these models is terrific for these high-powered engines.
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, especially when working with GM power.
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 GM alternator in the same manner as was the Jeep alternator; the same for the distributor, etc.
From basic (TBI) to advanced (TPI & Gen. III) 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 GM chassis. A simplistic but fair summary would state that a 1955 Chevy 283 and a 2004 LS1 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.
An installer's analysis of the Jeep's particular wiring diagram and the engine's wiring diagram will quickly reveal the wires that can be merged, connected and (in many cases) simplified or even eliminated.
This, our #2PRS, is a speed signal generator that connects to the Dana 20, QuadraTrac and New Process transfer cases. This VSS allows for pass-through of the speedometer cable to operate the conventional speedometer. This VSS gives the engine critical speed data for proper operation.
You can keep your Jeep's speedometer gauge as it is driven by the speedometer output of your Dana, QT and NP transfer cases. You can also keep your fuel gauge and AMP / volt gauge as factory. Your oil pressure gauge and water temp gauges can use the original Jeep sensors, as adapted into the ports on the engine assembly.
All aftermarket gauges can also be used. You can feed new, electronic Engine Temp, Oil Pressure, Tach and Speed gauges from the PCM if doing a Gen. III+ swap.
Factory steering in these Jeeps is usually adequate and there are no interference issues with any of the recommended engines.
If using Saginaw power steering, 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.
You will use the native power steering pump as native to your conversion engine.
All factory steering components are retained, including the power steering gear, drag link and tie rod. We recommend the use of the Vortec truck pans if installing a GM Gen III+, or otherwise a rear sump pan for other GM conversions. 1980's era FSJ Jeeps may require the removal of their panhard bar for clearance, which, in FSJ circles is often considered an improvement in any situation, since these leaf-sprung Jeeps have great lateral rigidity in their axles if the spring bushings and other factors are in good repair.
Novak engine mounts represent a tradition of innovation, strength, ease of installation and superior clearances for steering and exhaust systems.
This is essentially a non-issue with these FSJ Jeeps. Modern conversion engines often weigh less than the factory engines. The compression rate of factory springs is usually adequate, if sagging has not occured. Even the Big Block and Diesel engines should not affect the front springs much differently than factory engines.
A 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.
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 fairly tight fitting. The shorty, block-hugging style is the best bet.
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.
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.
You can run single or dual exhaust.
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.
Driveshaft angles do not present 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 Dana 20 (or other 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 redrilled for a new transmission mount unit. 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 44 and AMC 20 rear axles can withstand very ambitious engines. Such is the case for the front axles 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.
Hydraulic clutch release with a Chevrolet or Buick bellhousing is easy. See Novak's #HCR Series Clutch Slave Cylinder retrofit kit.
An in-depth discussion on this topic is covered separately, here. However, there are a couple of quick specifics that apply to these Jeeps:
This topic generally covers throttle, 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. As nearly all modern Jeeps and GM engines use sheathed cable for throttle control. More Generation III engines use a throttle-by-wire, in which case you will use the GM pedal, and connect the wiring as per OEM.
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.
We used the factory automatic column-shift anchor bracket and used simple rod-end bearings with a threaded rod, in which we placed a jog. The sector shift arm is fully adjustable.
Engine swaps aside, factory brakes may or may not be adequate. As a general rule, if the brakes were good before the swap, they will probably be sufficient after the swap.
It is up to the individual doing the conversion to ascertain whether or not to upgrade the braking system depending on how the Jeep is to be used. Brake systems are out of Novak's scope, but there are companies and shops that deal with brake upgrades if the installer deems it.
For engine clearance purposes on the FSJ Jeeps, we will note that ~1983 and later models used a larger diameter, double diaphram, vacuum brake booster. To clear some engines, it may be necessary to use a powerful and more compact hydro-boost system. It is not desirable to use the earlier, smaller diameter brake boosters as there would be a certain loss of braking effectiveness.
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 GM power into Jeeps for decades and these conversions are being done with greater frequency and success than ever.