GM engine conversions into these CJ Jeeps are simply great. These swaps are exciting, enjoyable, beneficial and well-documented as with these CJ 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.
Engine upgrades and transmission conversions began into these Universals since they rolled off the warships, but most successfully so since Chevrolet introduced is hallmark Small Block V8 in 1955.
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 scope of engines covered by this article include:
The rest of the pertinent history is largely mechanical, as discussed below. A "little" history is a difficult thing when discussing any Jeep CJ, but essentially, the CJ's of the 1976-1979 era were very similar to the CJ's of the 1972-1975 era. AMC hit their stride a bit in standardization and had fully converted over to their way of doing things by this time period. However, these CJ's were still based heavily still on the Bantam/Willys/Ford military Universal, in that they feature a compact design; narrow track and short wheelbase for weaving up, through and around obstacles.
The rest of the pertinent history is largely mechanical, as discussed below.
The AMC V8 was still available in these CJ's, though they were being increasingly detuned and complicated with emissions controls, and these things took their toll, and without much benefiting efficiency or economy.
The AMC 258 I6 was the most common engine in these Jeeps. AMC had left the 232 behind in the CJ by 1976. The 258 was always a pretty good motor, though never wholly exciting due to core design constraints. Carburation and tuning challenges are among the challenges that push owners over the edge into the world of conversion upgrades.
Jeep settled in on three transmissions in 1976, as below:
The above transmissions are appropriate to retain with a GM engine conversion. They are both plenty strong (the T18 especially so) and if the owner is happy with their gearing, marrying them to the new engine is a good option.
Jeep had two transfer cases available during this era. They continued on with the very successful Dana Model 20 with the T150, T18 and TH400. This strong gearbox is usually always retained in a conversion due to its durability and compact size.
The second transfer case avaialable was the Borg Warner 1305 & 1339 QuadraTrac. This transfer case was only available with the TH400 automatic.
We'll return to this topic in more detail, below.
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 CJ 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.
Many CJ swaps are likely destined to have automatic transmissions. As discussed above, 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.
No adapters are generally needed to marry the following GM automatic transmissions to their usually matching Chevrolet or BOPC engines.
TH350: Swappers should surely consider the GM TH350 automatic. The Turbo 350 is strong, compact, widely available and affordable to buy, service and build.
• The Dana 20 is adaptable to the TH350 with our#103 series adapter kits.
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, but only for CJ7 and longer Jeeps.
• The Dana 20 transfer case is adaptable to the TH400 by using our #124 series adapter kits.
700R4: This famous GM automatic overdrive is an option, but because of its length only for the CJ7.
• The Dana 20 transfer case is adaptable to the TH700R by using our #107 series adapter kits.
The following four and five speed transmissions are recommended for you to consider in your planning.
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. We will recommend the use of our #HCR Hydraulic Slave Cylinder Retrofit assembly on a Chevrolet & Buick bellhousings, as it is fully compatible with Chevy engines and the transmissions discussed below.
T150: If your Jeep has the T150 three-speed, it is an option. Though not suited for wild V8 power or punishing off-roading, mild V8's and V6's and all around trail use make the T150 a good match.
• Adaptability is not difficult, and is accommodated by our#G150 adapter assembly
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.
• Adaptability is straightforward, and is accommodated by our #1879 adapter assembly
Many CJ'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.
• The Dana 20 is adaptable to the SM420 by using our#422 series adapter kits.
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.
• The Dana 20 transfer case is adaptable to the SM465 by using our #462 series adapter kits.
Ford T18: Yes, the Ford T18 may also be an option for GM swaps. Adapting this transmission to a GM bellhousing is not difficult.
• The Dana 20 transfer case is adaptable to the T18 by using our #188 series adapter kits.
A good five-speed transmission with overdrive will fit the bill for some Jeep builders.
AX15: This reasonably strong five-speed transmission may be worth installing into your CJ7 (the CJ5 is usually too short). Adaptability of the AX15 to your GM engine is very good, and is accommodated by our #GMAX series adapter assembly.
The AX15 is easily adapted to the Jeep Dana 20 transfer case using our #152 series adapter kit.
NV3550: The NV3550 is a pretty tough transmission and can be married to GM power. Adaptability is achieved by our #GMAX series adapter assembly. Best for the CJ7. The CJ5 is probably too short.
The NV3550 is easily adapted to the Jeep Dana 20 transfer case using our #152 series adapter kit.
Options outside of these mentioned are usually not practical, useful, affordable or any combination of the three.
The stock Dana 20 transfer case found in these CJ 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.
Because of the rarity of requests we get to adapt the QuadraTrac to various transmissions, we do not many any adapter assemblies to retain this transfer case. However, if you'd like a gear driven transfer case instead, and would like to keep your axles, we recommend the Jeep Dana Spicer 18 as a replacement. It will fit very well into any of these CJ's and provide the proper offset to match an offset CJ7 axle as found behind the QuadraTrac. The Model 18 has the same adaptability options as the Dana 20 and the above transmission links will take you to the appropriate kits.
Some individuals ask us occasionally about trying to install Chevy style transfer cases like the 205 and others. They do not fit well into a CJ by virtue of their length, width and long adapter assemblies as designed for full-size trucks. Additionally, their gearing and other features do not lend them well towards the goals most are seeking with their Jeeps.
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 CJ?
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.
You're surely not doing the swap to go with a pansy powerplant, but do you need a V8? We'll help you rule out two extremes. Don't swap an engine in with any fewer than 3.8L and don't swap one in with any more than 400 c.i. Big Block engines are seldom appropriate. They do not fit as well and they could generate more power than the Jeep may be able to contain.
Now that these are ruled out, what engines in the middle do you like; are you familiar with; will pass your local emissions; will land within your budget; etc? Our favorite considerations for this Jeep include:
Ford motors are also a popular possibility, and these are discussed here.
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...
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.
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?"
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:
- Firewall clearance; a general rule is to leave yourself enough room that you can service the points at the rear of the engine without the removal of the engine from the Jeep. This includes any distributor, plugs, manifolds or other sub-systems. Note here that Jeeps have an indentation just off of center in the firewall for clearance with the factory I4 & I6 engine heads and valve covers. This is a very handy place to tuck a Chevy HEI V6/V8 distributor. Denting and especially cutting of the firewall looks quite terrible and will take away from the great look of your new engine.
- Frame rail clearance; it is usually exhaust manifolds that dictate location here. Most installations will require the engine to be offset 1" to 1-1/4" towards the driver side.
- Steering shaft clearance; Actually, more of a driving reason for the offset as listed above.
- Radiator clearance; your choice of water pump and fan (mechanical or electric) will establish your envelope here. Shorter water pumps and electric fans offer the greatest clearance.
- Hood clearance; will the hood close without any (remember that engines twist under torque) interference? Choice of air cleaner and air induction tubing is also an issue here. The high-hood Jeeps actually have a generous engine bay height envelope but you should still avoid mounting the engine too high for the sake of tunnel-to-transmission clearance and overall center of gravity.
- Front axle clearance; will your your axle, at maximum compression, threaten your oil pan? Most GM engines have rear sump pans so this should not be difficult.
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 CJ Jeeps decades ago and setting up a cooling system was a stifling challenge. Since then we now offer a bolt-in performance aluminum radiator with the outlets already configured for GM 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.
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.
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.
You can keep your Jeep CJ speedometer gauge as it is driven by the speedometer output of your Dana 20 transfer case. 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.
Installers will be pleased to hear that steering need change none or very little to perform the engine conversion. You will use a GM 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. If in doubt, the Camaro style brackets usually fit the best in these and many other Jeeps.
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.
You will use the native power steering pump as native to your conversion engine.
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 V6 and 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.
A lift is not required for the Jeep CJ 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. Fenderwell exit headers are not desirable for a variety of reasons.
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 CJ 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.
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 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.
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 AMC 20 and Dana 44 rear axles 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.
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.
Factory CJ brakes are usually adequate for nearly all engine conversions. 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.
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.