The Novak Guide to
Installing Chevrolet & GM Engines
into the
Jeep Universals, 1946-1971
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.
Because of the similarity in the 1946 through 1971 Universal type Jeeps, this article will cover the principles of GM conversions within these many models, with the exceptions as listed for each Jeep.
This article applies to the following "Early" Universal Jeeps:
CJ2A, 1946-1949
The CJ2A was preceeded by the CJ2, which were essentially a civilian MB that was sold in 1946. There were 1,453 of these sold before Willys could get tooled up on the actual civilian Jeep. These Jeeps should probably be left to the collectors. If you feel the need to do a conversion, consider another model.
The CJ2A was the first mainstream Universal Jeep, and have been benifitting from powertrain upgrades for decades. Their engine bays are somewhat compact, primarily in height and length.
As this is a "Low-Hood" Jeep, pay attention to the discussion, below, about engine choice and height.
The CJ2A featured the T90 transmission.
CJ3A Universal, '49-'53
As this is a "Low-Hood" Jeep, pay attention to the discussion, below, about engine choice and height.
The CJ3A featured the T90 transmission.
M38 Universal, '50-'51
The M38 was essentially a CJ3A in military configuration. They featured a 24 volt electrical system. Conversions on these rare and fantastic machines are discouraged on nice, original models.
The M38 featured the T90 transmission.
CJ3B Universal, '53-'64
The advent of the "High-Hood" Jeep was spurred by the upgrade to the taller Willys F-head engine. This opens up the taller Chevy V6 and Vortec motors for use.
Note that some of these 3B's had 6-volt electrical systems, which will need to be converted to 12-volt.
The CJ3B featured the T90 transmission.
M38A1 Universal, '51-'68
This military Jeep was the predecessor to the CJ5. featuring a high hood and the grille style that would stick with Jeep for the next 35 years.
The M38A1 had a larger, military spec steering gear, which will have a great tendency to interfere with a conversion engine. A change to Saginaw steering (discussed below) may be indicated.
These Jeeps have inset headlight housings, which want to interfere with the radiator. A custom radiator is probably the best answer here, as cutting up the headlights looks crude.
The M38A1 featured the T90 three-speed transmission and the T98 four-speed transmission.
CJ5 Universal, '55-'71
The most proliferate of the Jeeps of this era, the CJ5 is still a popular conversion candidate. Essentially all principles of this will apply to these Jeeps. All engines recommended in this article are fair game.
Tuxedo Park and other collectors quality CJ's are not probably not appropriate for conversions.
For transmissions, The CJ5 featured:
- The T90 three-speed transmission
- 1955 - 1971 with the 134 engine
- The T98 four-speed transmission (rare)
- 1955 - 1971 with the 134 engine
- The T86 three-speed transmission
- 1966 - 1967-1/2 with the Buick V6 engine
- The T14 three-speed transmission
- 1967-1/2 - 1971 with the Buick V6 engine
CJ6 Universal, '55-'71
The CJ6 will be essentially identical to the CJ5 as listed above, with one interesting exception: the longer automatic and manual transmissions that we discourage in all other early Universals, are fair game, including the:
DJ Dispatcher, '55-'64
The Jeep DJ was essentially a low-hood CJ with 2wd. Refer to the CJ3A, above.
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:
- Buick "90 Degree" V6
- Chevrolet Small Bock V6
- Chevrolet Small Block V8
- GM Generation III+ V8
- Ford 2000cc I4 (link to a separate article)
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.
A Little History
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 can be overcome.
Factory Engines
The Willys 134 L & F head inline-four engine was the most common of them all, spanning from 1941-1971. It was a good little engine. The Buick V6 came on the scene in 1966, itself spawned by aftermarket swaps.
Factory Transmissions
The Jeep Universals had only manual transmissions available during this era. They include:
- The T90 three-speed, as typically married to the 134 engines
- The T98 four-speed, as optionally married to the 134 engines
- The T86 three-speed, married to the Buick 225 engine
- The T14 three-speed, married to the Buick 225 engine
Transfer Cases
Jeep has usually excelled in its transfer cases. The Dana Spicer Model 18 was the transfer case in all of these models of Jeep.
The most successful conversions retain the gear-driven Dana 18 due to its strength, compact design, gearing and servicability. More on this in a minute...
Planning the Powertrain Conversion
Transmission Choice
It is crucial to discuss transmissions early on. They are sometimes more central to the conversion than the engine.
Though 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.
Automatic Transmission Options
Automatics are a tricky thing for these short Jeeps. However, the GM TH350 is a great option for any GM engine recommended in this article. The CJ6 has a couple more options, as noted in its section, above.
No adapters are generally needed to marry the following GM automatic transmissions to their matching Chevrolet or Buick engines.
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TH350: Swappers should consider the GM TH350 automatic. The Turbo 350 is strong, compact, widely available and affordable to buy, service and build. •The Dana 18 is adaptable to the TH350 with our#103 series adapter kits. |
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Manual Transmission Options
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.
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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. |
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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 |
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Jeep T98 : 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 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. |
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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.
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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 18 is adaptable to the SM420 by using our#422 series adapter kits. |
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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 18 transfer case is adaptable to the SM465 by using our #462 series adapter kits. |
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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 18 transfer case is adaptable to the T18 by using our #188 series adapter kits. |
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NP435: And, yes.the Ford NP435 may also be an option for GM swaps if your transmission has the extra front ears, as discussed here: adapting this transmission to a GM bellhousing. • The Dana 18 transfer case is adaptable to the T18 by using our #432 series adapter kits. |
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Options outside of these mentioned are usually not practical, useful, affordable or any combination of the three.
Transfer Case Choice
The Dana 18 is among the greatest transfer cases of all time
The stock Dana 18 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, compactness, gearing 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 these Jeeps 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.
Engine Choice
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.
Engine Size
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.
Our favorite considerations for this Jeep include:
- Chevrolet 4.3 V6 (high-hood Jeeps, unless doing a 3/4" - 1" body lift)
- Buick 3.8L or 4.1L "90 deg." V6
- Chevrolet Gen. I-II V8
- GM Gen. III+ V8
Installers considering the GM Gen. III V8 should note that low-hood Jeeps will not accept the taller Vortec intake assembly. For these Jeeps, this assembly should be swapped for a LS style, low-profile intake assembly.
If installed correctly, a 4.3L - though a tall engine - can fit into a low-hood Jeep. Images courtesy of customer G. Turberville.
This install features an 1-1/4" engine offset to the driver's side and the body was lifted at least 3/4" over stock.
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...
Emissions
Read our section on Emissions for a more in-depth writeup.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.
What to Pull From a Salvage Powertrain
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:
- The engine (don't let the obvious escape you).
- The accessory package and its brackets. The latter is especially important in that you don't want to waste valuable time and money chasing down the bracketry. The three major GM accessories that are native to the engine that you will install into your Jeep are the alternator, power steering pump and perhaps the air conditioner pump.
- The computer PCM or ECM that controls the motor (and possibly the automatic transmission) combo)
- The powertrain wiring harness. This is where individuals get unnecessarily uptight. This harness is quite obvious and surprisingly well self-contained. you will want all circuits to the engine's sensors and controllers, and you may opt to include the GM Power Distribution Center, also known as the relay center.
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.
The Jeep's Front Crossmember
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 are generally shorter at 25-5/8" and that do not have a distributor in the back of the engine - they are ideal motors.
Jeeps including the CJ3B and earlier models used a tubular front crossmember. The CJ5 & CJ6 featured a die-formed crossmember.
Tubular style crossmembers will have to be modified or, better, replaced when doing a Chevy Small Block V8 or GM Gen. III+ V8 installation. The installer may already be performing this operation for radiator, steering or strength purposes. V6 and shortened V8 installations do not require this step for the sake of the engine, but the conversion radiator will probably require the removal of the crossmember. The use of box steel tubing, welded into the frame channels, makes for the cleanest and easiest upgrade. It is also possible to make it such that the steering shaft (on Saginaw steering converted Jeeps) pass through a drilled hole in this crossmember.
More on this topic in Cooling, below.
Engine Placement
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?"
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.
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. If your GM pump pulley size is too large to clear your steering shaft, you can use a smaller pulley with no ill effects.
- 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 passenger 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.
Cooling
Sit tight here... We'll get through this with you:
There two major grille designs as concerns the radiator mounting interface on all these Early CJ Jeeps, the L134 / F134 style and the Buick V6 style (1966-1971). Though both grilles are different from each other, they are essentially a a flanged, pre-shroud style radiator intake. These are very easy to retain and work with when installing a GM V6 (Buick 90 Degree or Chevy 4.3) engine and usingNovak's KryoFlow #K-ECJ11S radiator.
GM V8 engines, such as the Chevy Small Block and GM Gen. III+ engines will require that the pre-shroud be removed and that the radiator be specially mounted against the grille. This has been the traditional method for many years. However, it may be possible, with the use of shortened water pumps (or even electric water pumps), shortened harmonic balancers and the use of a compact electric fan, to keep the original pre-shroud intact.
We recommend strongly that the reader take a few minutes and read the principles of cooling a Jeep.
Electrical
Powertrain Control ModulesThe PCM is an enclosed industrial-grade computer that, like most computers, has a processor, memory and IO connections. Newer PCM’s use an EEPROM chip; they are Electrically Erasable. This is also called flash ROM, and some users will equate this to the BIOS chip on their PC computer motherboard.
The computer works on if/then data tables and mathematical formulas in the ROM to interpret data streaming in from engine and vehicle sensors, including speed, temperature, exhaust O2, intake air flow, throttle position, crankshaft/cam position, brake, etc. The culmination of these data is processed to provide optimum fuel/spark delivery and in many cases, automatic transmission shifting points. Speed and rev limiters are also incorporated into some units. Once called an Engine Control Module (ECM), these computers have been appearing in vehicles since the early to mid-eighties. Their initial functions leaned more towards carburetor control primarily to keep up with tightening emissions standards. This was a bit of a dark time in automotive systems engineering as these early systems are now mistrusted to a degree by owner and mechanic alike.
Modern PCM's have evolved to be highly reliable, very functional and it is not difficult to integrate them into the Jeep engine bay with your new motor.
Some installations require PCM reprogramming. This is a service that is much more available for GM computers than any other, often through GM dealers, or local and national tuning shops.
A DLC connector in a Jeep, for an easy connection to your GM computer.
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.
Gauges
This, our #2PRS, is a speed signal generator that connects to the Dana 20. 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 CJ speedometer gauge as it is driven by the speedometer output of your Dana 18 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.
Steering
Engine conversions aside, steering really is a potential problem is these early 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.
Suspension & Engine Weight
you'll be replacing the following factory engine, whose weight is:
- Willys 134 CID I4, 470 lbs.
Engines you may replace it with may include:
- Chevy 4.3L V6, 425 lbs.
- Chevy Small Block V8 (Gen. I & II), 550 lbs.
- GM Gen. III+ V8 (iron blocks), 470 lbs.
- GM Gen. III+ V8 (aluminum blocks), 407 lbs.
- Buick 90 degree V6, 375 lbs.
Novak engine mounts represent a tradition of innovation, strength, adjustability, ease of installation and superior clearances for steering and exhaust systems.
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 Delivery
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.
Exhaust
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.
Driveshafts
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.
Crossmember & Rear Mount
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.
Axles
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.
Clutch
Hydraulic clutch release with a Chevrolet or Buick bellhousing may be worthwile. 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:
- If keeping the factory bellcrank clutch linkage system with your GM motor, you will use our #RAV6 clutch release arm to obtain the proper ratio.
- If you are making the move to a hydraulic release system, consider our popular #HCR Series retrofit kitsfor Chevrolet & Buick bellhousings. It is suggested that you use a later CJ or YJ master cylinder / pedal assembly, and that you laminate your firewall with painted or stainless steel in the master cylinder area for increased rigidity - as these earlier Jeeps used a thinner wall, not anticipating this usage.
Linkages
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. 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.
Brakes
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.
Summary
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.