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The Novak Guide to
Installing Chevrolet & GM Engines
into the
Full Size Jeeps,
Trucks, Wagoneers & Cherokees

Upgrade your EngineThe 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 accomodating 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.

Factory Engines

Factory Transmissions
The Jeep FSJ's featured the very widest variety of transmissions:

Transfer Cases
Dana 20Jeep has usually excelled in its transfer cases. The Dana Spicer Model 20 was the most commonn 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...

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 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.

Automatic Transmission Options
Every transmission we recommend on our website is avaiable 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.

The TH-350

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 TH-400

700R4: This famous GM automatic overdrive is an option with Chevrolet engines and probably the most popular transmission swap for the FSJ.

The 700R4

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).

4L60-E

 

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.

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.

The T90 Transmission

T14: If your Jeep has the T14 three-speed, it is an option. Like the T90 above, the T14 should not be used with milder motors and duty requirements.

The T14 Transmission

T15: If your Jeep has the T15 three-speed, it is a good, strong option.

The T15 Transmission

 


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.

The T98 Transmission

 

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.

SM-420

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.

SM-465

Ford T18: Yes, the Ford T18 may also be an option for GM swaps. Adapting this transmission to a GM bellhousing is not difficult.

T-18

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.

NP-435

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.

AX-15

NV3550: The NV3550 is a pretty tough transmission and can be married to GM power. Adaptability is achieved by our #GMAX series adapter assembly.

NV3550

 

Options outside of these mentioned are usually not practical, useful, affordable or any combination of the three.

Dana 20
The Dana 20 is among the greatest transfer cases of all time

Transfer Case Choice
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.

It is possible to install the Chevy 205 transfer case in some applications, though it is not ideal. Later FSJ Jeeps can use the Jeep NP231, NP241OR or GM NP241 (in some cases).

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
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.

Powertrain tilt measurement

Our favorite considerations for this Jeep include:

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

Emissions
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.

LS1 & Vortec V8 EngineYou need four or five key things:

  1. The engine (don't let the obvious escape you).
  2. 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.
  3. The computer PCM or ECM that controls the motor (and possibly the automatic transmission) combo)
  4. 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.

Vortec V6

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.

Engine Placement
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, then yes. Our bolt-in mounts will 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:

• 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
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.

• 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
RadiatorThere is ample room for good radiators in these Jeeps. One can have some factory radiators modified to match. Customers may also source cross-flow aluminum conversion radiators from Novak, on a request basis. As these Jeeps vary some through the years, contact us for application and pricing.

We recommend strongly that the reader take a few minutes and read the principles of cooling a Jeep.

A General Motors PCM or ECM computer

Powertrain Control Modules
The 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.

OBD II Compliant Jeep
A DLC connector in a Jeep, for an easy connection to your GM computer.

Electrical
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
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.

Jeep VSS
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.

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
Factory steering in these Jeeps is usually adequate and there are no interference issues with any of the recommende 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.

Suspension & Engine Weight
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.

Shown are the GM Gen III+ Engine Mounts

Novak engine mounts represent a tradition of innovation, strength, ease of installation and superior clearances for steering and exhaust systems.

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.

Tight fitting headers are a must

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.

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.

One way to run a Chevy to YJ exhaust

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.

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.

Driveshafts
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.

Transmission Crossmember Mount
This popular rear mount is strong and easy to set up with any Jeep swap. See our lineup of rear mounts, here.

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 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.

Clutch
An in-depth discussion on this topic is covered separately, here. However, there are a couple of quick specifics that apply to these Jeeps:

Hydraulic Clutch Retrofit Kits
Hydraulic clutch release with a Chevrolet or Buick bellhousing is easy. See Novak's #HCR Series Clutch Slave Cylinder retrofit kit.

Linkages
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.

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.

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.

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.