Engine upgrades and transmission conversions began in 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.
This article applies to the following "Early" Universal Jeeps:
These were built on a CJ6 frame but have somewhat different drivetrain components than the CJ5/CJ6.
Though these Jeeps were similar to the CJ Universals of the same era, they were supplied with the Dana 20 transfer case.
The early versions had a Spicer Model 30 rear axle and a Model 21 front axle. The Model 30 rear end was prone to failure. Later models solved this problem by using a Spicer 44 rear end. The front axle was upgraded to the Model 27.
The C104 was also built on a CJ6 frame. The C104 received a new front end, ostensibly to accomodate the longer AMC I6 and V8 engines. The distinctive Jeep look was set aside for a new grille, hood and fender design.
For this particular model, the tread width increased, GM Saginaw steering (manual and power option), bigger brakes and many other changes were introduced in 1972.
Because these 1972-75 Jeeps had an I6 or V8 option, they are simple to convert to GM V8 power.
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.
No straight-six this side of the industrialized world will ever fit right. A Big Block engine in one of these small Jeeps would probably be inappropriate to the point of being funny.
We recommend the following engines as top choices:
GM engine conversions into these Jeeps are simply great. 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.
These early Universals were less far removed from the "Blitz Buggy" type thinking that spawned the MA, MB and GPW militaries. These Jeeps were compact, light and agile like mountain goats. Jeeps today seem to get larger with every generation.
These Jeeps do have a few conversion challenges due to their compact size, but these are easily overcome.
The Willys 134 L & F head inline-four engine was the basic motor from 1966-1971. It was a good little engine. The Buick V6 came on the scene in 1966, itself spawned by aftermarket swaps that were occuring with increasing frequency.
The Jeep Universals had only manual transmissions available during this era. They include:
Jeep has usually excelled in its transfer cases. The Dana Spicer Model 20 was the transfer case in all of these models of Jeep.
The most successful conversions retain the gear-driven Dana 20 due to its strength, compact design, gearing and servicability. More on this 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.
The world of automatics open right up for the Jeepsters, as they have longer wheelbases than their short CJ counterparts.
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.
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.
• 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 with Chevrolet engines.
• 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 1980-1990 CJ or YJ master cylinders and related components is not difficult. Rivoting a layer of stainless steel to stiffen the firewall for a master cylinder is a good idea. 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.
T90: If your Jeep has the T90, it can be adapted to a GM powerplant. It is a fairly strong transmission and many individuals retain it against their new motors.
• 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.
T14: If your Jeep has the T14 three-speed, it is an option. Though not suited for wild V8 power or punishing off-roading, mild V6's and easy trail use make the T14 a good match.
• If your T14's factory Buick style adapter is not present, adaptability is acheived with our #1415 adapter assembly
T15: If your Jeep has the T15 three-speed, it is a good, strong option.
• Adaptability is acheived with our #1415 adapter assembly
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.
• Adaptability is possible. However, because of the variations in the T98's that Jeep produced, contact us and well get some data from you before recommending an 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.
• 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.
• The Dana 20 transfer case is adaptable to the T18 by using our #188 series adapter kits.
• The Dana 20 transfer case is adaptable to the T18 by using our #432 series adapter kits.
AX15: This reasonably strong five-speed transmission may be worth installing into your Commando. 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.
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 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.
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 Jeepster 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 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.
You're surely not doing the swap to go with a pansy powerplant, but do you need a V8? Maybe. V6's do fit better and offer good power.
Injected vs. Carbureted
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.
C104's do not have this concern.
In the C101, individuals installing Small Block V8's should optimize the length of their engines by using a compact HEI distributor so the engine can sit as close to the firewall as reasonable. The installer should also use the short style water pumps and pulleys for maximum radiator clearance and crossmember clearance.
Generation III engines that do not have a distributor in the back are ideal here.
The C101 and C104 formed style crossmembers need no modification for a V6, and they need no modification for V8 engines if the engine length optimizations above are performed.
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:
There are too many ways and too many different grille designs and engine installation methodologies for the aftermarket to zero in on some kind of standardized radiator installation. The installer should plan on installing a compact radiator in the neighborhood of 18" tall by 22" wide.
C101 with the Buick engine had a flanged, pre-shroud style radiator intake. These are very easy to work with. Other Jeeps will take a bit more effort and fabrication.
We recommend strongly that the reader take a few minutes and read the principles of cooling a Jeep.
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's 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 if doing a Gen. III+ swap.
Engine conversions aside, steering really is a potential problem is these C101 Jeeps. The Ross steering linkage system can be loose and high maintenance, and from the standpoint of the conversion, it can get in the way of things. If you are going to keep factory steering, we recommend a remote oil filter adapter kit (commonly available from speed shops), for the Small Block engines as it will otherwise interfere. Additionally, it is necessary to grind a small flat on the edge of the block above the oil filter to gain clearance for the pitman arm.
Buick V6's do not have this requirement.
If the steering wheel is turned to the extreme left the pitman arm will hit the bellhousing. This is cured by removing the pitman arm and indexing it one spline tooth forward away from the bellhousing. The steering wheel is then put back on the "high spot" of the worm by shortening the steering connecting rod. Do this by increasing the two bends in this component or by cutting and welding. An alternate to this method is to leave the aforementioned parts intact and grind a notch in the bellhousing to regain the lost pitman arm travel, however, it is simpler to reposition the pitman arm.
If converting to 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.
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 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 Universal 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 Dana 44 rear axles can withstand very ambitious engines. Such is the case for the front Dana 25 & 27 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.
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.
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.