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CHAPTER 2

ENGINE

Engine performance modifications in the Jeep community are rather different from most other forms of automotive enthusiast engine modifications. A Jeep engine is most often modified to provide increased low-end torque rather than increased high-end horsepower because the needs of the trail are different from those of the dragstrip. Jeep engines tend to run at slow speeds and slow vehicle movement on the trail, which puts extra stress on the cooling system. High-compression, high-horsepower engines usually do not tolerate the kind of driving conditions Jeep owners might expose their Jeeps to.

This 1977 CJ-7 was a factory V-8 equipped Jeep with a TH400 automatic and Quadra-Trac transfer case. Of all the modifications, upgrades, and enhancements, the V-8 has remained stable with just enough performance modifications to perform well on- and off-road.

Even though the CJ series was discontinued years ago, it is possible that local and federal emissions laws are still applicable. Research into emissions laws should be done before digging into modifying your Jeep’s engine to avoid violating laws and rules, which could result in the inability to pass a smog test. Many aftermarket parts are smog legal and many do not alter emissions systems at all. Typically, swapping an engine of a newer model year is permissible by emissions laws, as long as comparable emissions equipment is retained. With the advanced age of the AMC-era CJ, it’s hard to imagine swapping an older model year engine into the Jeep.

Factory Engines

Factory Jeep engines were briefly discussed in Chapter 1, so here I dig more into “actually useable” Jeep engines, including the advantages and disadvantages of each. Two 4-cylinder engines were offered in the CJ during the AMC era. Although both were functional engines, their lack of power and torque make them poor choices in a modified CJ, so they should be avoided and/or swapped. In the following few paragraphs, I discuss the I-6 and V-8.

AMC I-6

The 232 and 258 I-6 engines are similar in design and use many of the same components. The 258 was a far more popular engine in the AMC-era CJ than the 232. The engine is well known as reliable and provided a significant amount of torque for its size, thanks to its long compression stroke. The 258 has proven itself as a workhorse engine in a CJ and can provide years of reliable service to its owner. The low-end torque of this engine and the low gears of a CJ is a near-perfect combination. However, there are some gotchas with this engine, and perhaps the biggest one deals with the horrific carburetor system found on 1981 and later CJs.

The AMC In-line 6-cylinder powered the CJ and so many other Jeep vehicles reliably and effectively for more than 30 years. This Jeep’s 258 is showing its age and use from all the years of mud, grime, and dirt present on it. These engines were true workhorses that were capable of 250,000 miles from brand new to totally abused.

AMC V-8

The AMC 304 V-8 is a fun engine for a CJ and even in totally stock form can provide plenty of power and torque to throw a CJ around on the street and trail. Although the 1970s smog-laden V-8s weren’t known for their performance, with a little help they can come alive. AMC V-8 engines were popular in the AMC muscle cars they came in, such as the Javelin and AMX. Thanks to those cars, a space was created in the performance aftermarket for the AMC V-8, and many upgrades and modifications are available. V-8–powered CJs running fenderwell headers and glasspack mufflers are an icon of the late 1970s.

The AMC Tall Deck V-8 engines were often accused of being copies of other manufacturers’ engines when in reality the engine was its own creation. The thing that separates the Jeep from other types of automotive enthusiast crowds is that a dirty, muddy engine is considered more attractive than shiny parts. Evidence that the Jeep is used the way it is intended only makes onlookers more interested.

Modify, Rebuild or Swap?

Before modifying your factory Jeep engine, consider its condition. Is it worth modifying, is it too far gone and not worth rebuilding, or even further swapping? Some inspection and a few tests should be performed on your Jeep’s engine before making this decision. A good-condition engine that is ready to modify should stand up to the added performance from the modifications. A rebuild candidate may be a fair-running engine but due to maintenance neglect or excess wear, this engine would benefit from a rebuild, along with modifications. A freshly rebuilt engine can be as good as new and can revitalize a Jeep. In the case that the engine may cost too much to rebuild or is beyond rebuildable condition, a replacement or swap should be considered.

Inspection and Testing

An engine in running condition is a good start, but how well it runs and how well it was maintained are just a couple of items that need further examination. Starting on the outside, inspect the cleanliness of the engine. Excess grease and gunk on the outside of the engine can mean there were unfixed leaks from old gaskets or worse, cracks. This grime hides problems and can cause the engine to run hot or possibly even catch fire. This book doesn’t focus on the specifics of rebuilding engines; consult an appropriate guide specific to your engine for more detail.

Finding grime like this inside your engine may mean a rebuild is in order. Grime in the rocker arm area usually means it’s everywhere. Changing oil and filter according the manufacturer’s specifications prevents this, even on an old engine. Complete disassembly and professional cleaning is the only real way of removing the contamination.

Compression

Compression testing can indicate the condition of the valves, valveseats, and piston rings. This simple test is performed using a compression tester that threads into the spark plug hole, cranking the engine (without it starting), and noting the pressure measured. Pressure numbers vary across engine types and years. In reality, the actual pressure number isn’t as important as the consistency (10-percent variance) of pressure among cylinders. If each cylinder measures a similar pressure, the engine’s valves, valveseats, and piston rings could be considered in sound condition.

Test an engine’s compression with the ignition system disconnected and all spark plugs removed. Thread in the compression tester and crank the engine using a remote starter switch or with the aid of another person on the key. Be sure the transmission is in park or neutral. Take note of each cylinder’s pressure and compare after the test is complete. Similar pressures in all cylinders indicate good balance and even wear, desirable if the compression is within specification, which is around 120 to 140 psi for both the I-6 and V-8.

AMC I-6 and V-8 engines in good condition generate pressures greater than 100 psi with 120 to 140 psi being within spec. A consistent low reading across all cylinders could be normal but may indicate a flat, worn-out engine. If a cylinder measures low, adding a teaspoon of oil to the low cylinder and repeating the test will indicate if bad rings or valvetrain cause the low pressure. No change in pressure from the oil test can indicate a holed piston or blown head gasket. Low pressures might warrant a full inspection and rebuild.

Engine Oil

Draining and inspecting the oil can give an idea of the conditions inside. Most people know that the engine oil provides lubrication to the close tolerances of the engine’s bearings but it can also suspend contaminants within. New oil is a nice, clear amber color and quickly turns to a blackish color from contaminants. Inspecting the oil for its texture and smell can indicate a problem; gritty oil can be a sign that the oil is very old, along with an old filter.

If other fluids come out with the oil, such as coolant, this indicates the likelihood that there is a gasket leak or crack in the block. Frothy or milky oil can contain coolant or water. If the Jeep was driven in deep water, it’s possible that water has entered the engine through the vents.

Coolant

Draining the coolant from the engine and inspecting it for rust or corrosion can indicate the condition of the cooling system within the engine and radiator. The presence of rust can indicate the water-to-coolant ratio was too weak and the water was causing the cast iron to rust. In addition to rust, a weak coolant ratio can result in corrosion to copper components. Periodic testing of the coolant ratio is simply done using an inexpensive coolant tester.

Interior

Interior inspection of the engine is definitely more involved and requires some disassembly of the engine. Starting with the valvecover(s), remove the cover and inspect the rocker/valve area and components. If this area of the engine is covered with grime and old, thick, sticky oil (known as sludge), this is a good indication of very old oil, overheating, and/or poor-quality oil. If the condition of this area is very poor, it’s likely the rest of the inside of the engine looks the same.

Inspection of the interior of an engine is a good indication of the extent of a rebuild. The removal of the oil pan or intake manifold on a V-8 (requires draining antifreeze) gives a view of the condition of the interior of the engine. The smell or presence of non-oil fluids such as water, antifreeze, or gasoline can indicate trouble.

A few products can be purchased to help remove sludge; many (if not most) aren’t very effective and can result in engine damage by releasing stuck sludge into the engine, clogging bearings and passages. Proper sludge removal is generally best done by full disassembly and cleaning of the engine.

Summing It Up

An engine that passes the inspection and tests could be considered worthy of modification. A minor rebuild during modification, such as new gaskets and seals, should be considered, as well as replacement of certain components that are typically a hassle to replace when the engine is fully assembled, such as the thermostat, hoses, belts, and water pump.

Rebuilding

If, after inspection, a rebuild is in order, it is best to pull the engine and further inspect crankshaft and connecting rod clearances to determine if machine work is needed. Consult an engine rebuild guide for your particular engine to determine inspection specs.

If the engine checks out, a rebuild can be far less expensive than a new engine and can be performed by a do-it-yourselfer to save some expense. Certain things such as engine cleaning should be performed by a professional to ensure all contaminants are removed from even the hard-to-reach places in an environmentally sound and efficient manner.

In addition, consider a professional valve job while the engine is out and apart, again another overlooked job so easily done at this time. If rebuilding an engine is not in your bag of tricks, a good engine shop should be able to perform the rebuild, including checking proper clearances and machining if needed.

Bent pushrods from a past broken timing chain combined with age, dirt, and grime made this engine run poorly, and after years of neglect a rebuild was needed. Bored .020 over, cleaned, and new bearings made this engine like new again. During assembly, a new performance cam, intake, and a fresh coat of factory color paint made this engine ready to go back into place.

Replacement or Swap

If the existing engine is beyond repair, a decision to replace the factory engine with a same type or swap to another type needs to be made. Typically, replacing the engine with the same type is the least expensive option because the expense of a swap and the costly items such as adapters, radiators, mounts, exhaust, etc., that go with it will not be incurred.

If the choice is replacing the engine with a similar type, consider factors such as engine size; perhaps an AMC 304 would be best replaced with a 360 that bolts right in.

Finally, deciding to install a used replacement engine in good shape is considerably less expensive than a crate engine.

Performance Parts and Modification

Increasing the performance of your Jeep’s engine can be achieved with a variety of additions and modifications. Because the goal is to build a Jeep that performs well on- and off-road, the modifications are not to build a 1,000-hp race engine but rather a good-torque and good-power engine. The beauty of off-roading a Jeep is that horsepower is not always as important as it may be in other automotive circles.

A rebuilt AMC 401 in this Scrambler provides enough horsepower to easily propel this Jeep in the passing lane. The nature of the 401 and thoughtful performance additions keep the engine producing plenty of high horsepower for some fun while maintaining the low-torque “tame” for those slow, controlled trail maneuvers.

Much of the day on the trail is spent moving at slow speeds and excess horsepower usually results in poor drivability, overheating, and broken parts. This fact allows a Jeep owner to invest a reasonable amount of the Jeep funds into performance parts that actually make a difference without going overboard. The saved funds can be put into things that matter more on the trail, such as traction systems, gearing, suspension systems, and everything else.

Here, I generalize on performance parts and focus on common modifications that enhance performance.

Factory Engine Modifications

Because most Jeep owners find themselves with a factory engine, much can be done to both the AMC V-8 and I-6 to enhance their performance. It is fortunate that both of these engines (for the most part) can serve the Jeep well with no modifications, but really, why would you want this? Because the engines are so usable out of the box, this suggests that anything that is done only serves to make the engine better.

AMC I-6

The most common I-6 in a CJ is the 258-ci (4.2L), which is a good engine with excellent low-end torque. The biggest drawback to this engine is the Computerized Engine Control (CEC) system found on the 1980s-era 258. The performance of these systems was barely adequate when the Jeep was brand new; the last CJ rolled off the assembly line more than 30 years ago so it’s safe to assume performance will be considerably worse.

Clifford Performance has a long-standing excellent reputation for combining proven components to improve the Jeep’s I-6; this shop is a good starting point for ideas and solutions.

The 1980s CJ I-6 brought with it the dreaded CEC system. Seemingly miles of vacuum lines and incomprehensible carburetor system made this engine a poor performer even at its best. Swapping the CEC for a better system can free up much space.

Stroker Engines and Kits

Perhaps the ultimate in AMC I-6 performance comes from a stroked 4.2L. Stroked engines use larger bore pistons and a longer stroke crankshaft to increase the engine displacement up to 4.7L. Stroker I-6 engines can make up to 300 hp and 350 ft-lbs of torque. Hesco, Clegg, and Golen produce crate stroker engines and stroker kits that provide significant power and efficiency gains. The options available from these companies range from direct drop-in replacement crate stroker engines to turnkey multi-port electronic fuel injection (EFI) engines to full-on supercharged engines.

I-6 Induction System

Replacing the whole CEC is the best start for a 258, and best results come from either installing an aftermarket intake with a performance carburetor/throttle body fuel injection or installation of an electronic fuel-injection conversion from a 4.0L HO engine.

A few aftermarket performance parts companies, such as Offenhauser, make aluminum intake manifolds for the AMC I-6, and perhaps most notably, Clifford Performance with its extensive line of AMC I-6 performance products. These manifolds allow installation of performance carburetors or throttle body fuel-injection systems.

Typically, the manifolds are designed to use 4-barrel carburetors but can be adapted for other carburetor types. Unless the I-6 is capable of handling a large 4-barrel, that is, the engine was stroked and/or is running performance heads and a performance cam, a small 4-barrel carburetor should be the limit.

This CJ-7 runs a perfect example of a performance I-6 that is well paired with the Jeep’s transmission and drivetrain. A CEC-less, rebuilt 258 running a Clifford intake, Howell TBI, header, and TFI ignition lead the swapped T176 transmission and TeraLow-equipped Dana 300 transfer case.

The Howell TBI system is specially tuned for the I-6 in the CJ and provides computer-controlled efficiency to make the engine run at its best. TBI systems provide for quick starts and smooth trail running, especially in situations that flood most carburetors. The Howell kit includes all sensors, fuel pump, and components to easily swap out a troublesome carbureted system.

For a more stock engine, many Jeep owners have used the Weber 38/38 2-barrel carburetor with excellent performance results. The more adventurous Jeep owners convert the I-6 to a Howell EFI throttle body injection (TBI) system. This complete system brings the CJ a bit more modern. The TBI system performance is excellent off-road and improves starting in both hot and cold weather.

Mopar makes an EFI system for the 258 that is essentially a fully contained induction conversion for the Jeep I-6. This system replaces the entire induction system with a modern fuel-injection system nearly identical to the one found on the 4.0L HO engine that Wranglers, Cherokees, and Grand Cherokees ran until 2006. This system requires a fair amount of wiring and sensor installation but is installable by most DIY-type Jeep owners.

4.0L Head Conversion

The 4.0L engine used in Jeeps from 1987 until 2006 used an improved head design that is compatible with the 4.2L engine, with a minor modification to seal off the small, triangular cooling passages on the intake/exhaust side of the head with epoxy. A common practice is to lightly stuff the ports with packing peanuts (which dissolve), seal with epoxy, and smooth the epoxy when dry. With this swap, use of a 4.0L exhaust manifold or header is required; the stock intake may be retained if desired.

This swap, when combined with a performance carburetor, TBI, or MPI setup from a 4.0L, wakes up a tired 4.2L and increases engine efficiency and off-road performance. The longer stroke of the 4.2L combined with the head improvements can yield an I-6 with more than 200 hp.

I-6 Camshafts

A few high-performance camshafts can be found for the I-6 from companies such as Clifford, Comp Cams, and Crower. Cams that improve the low-end torque (in the 208 duration and .448 lift range) are the best choice for a Jeep that sees the trail and street. Clifford performance makes a complete cam kit for the Jeep 258 that includes all the components such as springs, pushrods, and lifters. This kit increases the I-6 torque curve to produce a flat torque curve off idle to 4,500 rpm, especially useful off-road at slow speeds.

I-6 Exhaust

Headers versus manifolds is a debate that will last as long as engines still have them. The I-6 was known to crack factory exhaust manifolds, but on the flip side headers are known to blow gaskets and leak exhaust. Proper headers increase flow, resulting in better horsepower and torque. Clifford, Hedman, PaceSetter, and Borla make quality headers for the I-6 in various constructions and configurations.

Stainless and ceramic coatings provide long life and good looks. Some I-6 headers use a 3-into-1 tube design to provide a dual exhaust; the traditional 6-into-1 remains most common. Performance differences between the two can be negligible and insignificant to the dual-exhaust routing headaches that occur.

A good muffler can also help with performance and make the Jeep sound a little better. A loud exhaust gets old very quickly on a trail Jeep; consider a muffler that sounds good but is quiet enough to not annoy. Flowmaster mufflers combine good flow with good sound and solid construction that can handle the punishment of off-road use.

A Clifford header provides smoother exhaust flow from the I-6 with some added tone to give the Jeep’s sound some personality. Headers can increase torque and power 30 percent, depending on configuration and engine specs. Dual- and single-outlet headers are available for the I-6.

I-6 Ignition

The Jeep I-6 used a points system until 1976 and the Motorcraft electronic ignition system until 1986. The Motorcraft system worked well but was prone to sudden failure without warning. Many Jeep owners made it a regular habit to carry a spare ignition module in case of a failure.

The high-energy ignition (HEI) system is considered the most reliable classic ignition system and only requires a single wire for power. A GM HEI-style distributor can be adapted to work in the I-6 with only a gear modification. These conversion distributors can be found ready to go and are easy to install. Davis Unified Ignition makes a top-of-the-line HEI-style distributor for the Jeep I-6 that provides the ultimate in ignition performance.

An alternative to a complete HEI swap is adapting a Ford TFI ignition to a Duraspark distributor.

AMC V-8

Like the Jeep I-6, the factory 304 V-8 is a good starting point in a CJ, even in its stock form. The messy emissions controls and equipment of the 1970s stifled the small V-8, but with a little help this engine can provide plenty of low-end torque and some extra horsepower to make the Jeep feel like a muscle car. Swapping an AMC 360 or 401 is a bolt-in job and can provide a larger boost to the Jeep than might be possible with the 304. The AMC V-8 has a fair amount of aftermarket performance parts available, and finding a proven combination is not a difficult task.

The Generation 3 or Tall Deck AMC V-8 was used from 1970 until 1991 and was available in 304-, 360-, 390-, and 401-ci configurations. These engines share most components such as cylinder heads, intake manifolds, camshafts, etc. A 304 or 360 are probably the most common and easiest to find. Both provide a good start to a Jeep engine build.

A few varieties of the high-output electronic ignition systems are available for I-6, including a less common but effective Ford TFI conversion. This system uses a more modern ignition system with a similar function and performance to the GM HEI system. The TFI conversion uses some of the stock components while most importantly replacing the Ford Duraspark module.

Even stock, the AMC 304 has plenty of torque for the Jeep. This restored 1978 Golden Eagle CJ-7 is still powered by the stock engine attached to the factory TH400 and Quadra-Trac. A set of fenderwell headers is about the only performance addition.

V-8 Stroker

Unlike the I-6, the AMC V-8 engine has few stroker options available, built mostly of homegrown combinations using mixed parts and special crankshaft grinds. The cost and compromise may make it not worth it for a Jeep used on the street and trail. Power and torque gains found in the I-6 stroker make the work make more sense. In contrast, the AMC V-8 running in its factory sizes serves the Jeep easily, even with light modifications. I suggest you skip this option; it’s just not worth the effort to stroke an AMC V-8 for a CJ.

V-8 Induction System

The stock AMC V-8 used a Motorcraft 2-barrel carburetor that was surprisingly well suited for both on- and off-road use. These carburetors were well known for reliability and maintenance-free use. A variety of intake manifolds were used on the CJ V-8; design differences were often to accommodate emissions systems such as exhaust gas recirculation (EGR).

A shiny new Edelbrock Performer intake manifold provides the perfect performance enhancement for a V-8 in a Jeep. This AMC version is destined for Bryan Sterner’s 1980 CJ-7 that is running the stock 304. A proper-size 4-barrel carburetor and matching Edelbrock Performer camshaft completes the package.

Companies such as Edelbrock, Offenhauser, and Weiand make performance manifolds for the AMC V-8; most are made to work with 4-barrel carburetors and can be adapted to work with modern throttle body fuel-injection systems. The Edelbrock Performer series intake with its matching camshaft make an excellent combination to make some extra torque and horsepower from the engine that is nearly perfect for an on- and off-road Jeep. Most aftermarket manifolds can be purchased with or without emissions capabilities.

A small (470 to 670 cfm) 4-barrel carburetor or throttle-body fuel-injection system added to a V-8 running an aftermarket intake and cam provides better throttle response and starting. Two excellent carburetors for use in a Jeep are the Edelbrock Performer and the Holley Truck Avenger. When either is combined with the combination above, optimum performance on- and off-road can be achieved.

Holley carburetors have always been known for their exceptional performance, except when used off-road. The front and rear fuel bowl combined with the bowl venting location often caused fuel to dump into the throttle body when ascending or descending hills, resulting in flooding and stalling. Holley answered the call of off-roaders with a specially designed off-road carburetor called the Truck Avenger, featuring special metering blocks and off-road crossover vent tube.

The Edelbrock Performer Series carburetors are based on the Carter AFB and come in a variety of flow capacities. The integrated side-bowl design of the carburetor makes its off-road performance excellent compared to most other performance carburetors. The pre-tuned bolt-in design makes this a popular aftermarket carburetor.

The Edelbrock carburetor is based on the Carter 4-barrel but is specially tuned for the Performer Series products. The integrated main body side bowls and simple design make this very effective in a Jeep, especially off-road.

The Holley Truck Avenger is based upon the Holley 4160 with several modifications to make it perform in off-road conditions. Most notable is the crossover vent tube to prevent flooding on ascent and descent and spring-loaded needle and seat to control fuel flow. The Holley Truck Avenger is available in three CFM sizes. A 470-cfm suits the 304 and a 670-cfm suits the 360 and 401. Avoiding the tendency to over-carburete an engine; using the 770-cfm pays off in the form of performance and no tearing eyes from fumes.

Holley, Howell, and MSD produce electronic throttle body fuel-injection systems that replace the carburetor and can provide a high level of all-around performance, most notably in off-road conditions and starting in both cold and hot environments. These systems can operate with full, minimal, or no tuning; often through the use of the many sensors, the system tunes itself constantly while operating. A small drawback of these systems is the complexity of installation and the added potential points of failure.

Throttle body injection (TBI) systems offer a modern replacement to a traditional carburetor. The Holley Pro-Jection TBI was a popular system in the off-road community. Its simple design, easy starting, and steady engine performance at any angle were just a few of the positive features. This Holley Pro-Jection system has been running on this 350 Chevy-equipped 1985 CJ-7 for more than 20 years. Holley replaced the Pro-Jection system with the updated Holley Avenger electronic fuel injection (EFI) system.

In general these systems operate confidently, with most failures occurring with the fuel pumps. You can solve this by always carrying a spare on the trail. These systems can be expensive and the benefits may not outweigh their complexity and price.

V-8 Camshafts

A variety of camshafts are available for the AMC V-8. Many are made for strip or other racing applications, but a few exist that are perfect for the Jeep. As I mentioned before, the Edelbrock Performer Series components are nicely matched to each other. The Performer camshaft for the V-8 provides a nice power curve that increases low-end torque and mid-range horsepower. This mild build camshaft does not alter the low-end idle of the Jeep as a high-duration camshaft does, which is important when driving off-road slowly.

The small lobes and short duration on the stock camshaft in most engines made for smooth, fuel-efficient engines but at a cost to performance. Replacing a camshaft is an involved project that produces noticeable results compared to many other performance modifications. Choose a cam matched to the intake system for the best performance results. High-lift and long-duration cams sound nice but are difficult to drive off-road, as they sacrifice low-end torque for high-RPM horsepower.

Other camshafts in the 204/214 duration and 448/472 lift ranges provide added low-end torque. In addition to upgrading a camshaft, upgrading the engine’s timing chain to a dual roller completes the package.

V-8 Exhaust

The 1970–1991 AMC V-8 used a dogleg exhaust port that provided 20 percent better flow than prior-generation AMC heads. The factory V-8 used cast-iron exhaust manifolds that used a combining Y-pipe to exit the rear driver’s side of the Jeep. The factory exhaust manifolds flow well for the purpose of a street- and trail-used Jeep; they can be retained and when combined with an upgraded exhaust, increase flow and torque.

The dogleg port seen on this dirty AMC cylinder head is a unique feature of the AMC tall deck engines introduced in 1970. The extra port provided increased flow compared to the prior design.

Typically, a single exhaust is most common on trail-used Jeeps. The low-end torque on both the I-6 and especially the V-8 is better with a single exhaust system.

Although exhaust manifolds perform best on a street- and trail-used Jeep, a Jeep with headers, especially fenderwell headers, adds a cool factor that is hard to deny. Fenderwell headers exit the Jeep’s engine compartment just behind the front wheels. A small muffler or cherry bomb muffler is typically used to quiet the exhaust. Almost all fenderwell header Jeeps are loud, so you need to be able to tolerate the noise that comes with the classic look.

Headers improve exhaust flow slightly over the factory manifolds, and the use of matched tube-length headers provides balance to exhaust output. Fenderwell headers are troublesome when used off-road because they may become damaged on obstacles and interfere with the often-used side rocker protection rails. In-frame headers allow for the exhaust to be run within the frame rails, but space is tight on the passenger’s side due to the transfer case drop.

Fenderwell headers hold both a performance enhancement and a visual appeal. Many 1970s-era V-8 CJs can be seen running these type of headers with small mufflers or glass-packs. With these headers comes a fairly loud exhaust sound, which is sure to wake the neighbors.

Speaking anecdotally, many Jeep owners who have outfitted their Jeeps with headers of either kind have removed them to revert back to the factory manifolds. The reasons given for this are often constant exhaust leaks, excess underhood heat, and noise.

High-Performance Single Exhaust

An effective single exhaust using the factory manifolds must be fabricated by a professional shop or using sections of pipe and mandrel bends. Using 2-inch leader pipes running through a performance Y-pipe with a 3-inch outlet starts the system. Some run the leader pipe on the passenger’s side forward and under the oil pan. An alternative is squeezing the passenger-side leader pipe over the front driveshaft and through the gap between the oil pan sump and transmission. To fit properly in the latter method, a lift kit is often essential and the pipe may need to be flattened slightly over the driveshaft. From the performance Y-pipe, the system exits the rear after passing through a performance 3-inch muffler and catalytic converter (if needed).

Flowmaster makes many varieties of mufflers that can fit a Jeep. Their durable construction and performance makes an excellent choice off-road. This free-flowing system can provide more low-end torque than a dual system. A single 3-inch pipe flows more than dual 2-inch pipes. ■

The 3-inch outlet leads into a performance Flowmaster muffler with 3-inch inlet and outlet. The 3-inch pipe continues from the muffler to the rear of the Jeep. Low-end torque from the single exhaust was an improvement over the old dual 2-inch exhaust system. The Flowmaster Y-pipe and muffler maintains the deep, throaty tone of the V-8, even though exhaust is only through a single pipe.

To allow clearance for the front driveshaft and prevent the crossover pipe from being too low, the passengerside pipe routes forward, looping around the oil pan sump. After completing the curve, it joins the driver-side pipe at a smooth transition Y.

The performance Y-pipe setup keeps the crossover pipe up and out of the way of trail obstacles. This setup in a 1978 CJ-5 squeezes the pipe over the top of the front driveshaft for extra clearance and it passes in front of the T-18 leading to the Y-pipe collector. It was necessary to flatten the pipe at the driveshaft for proper clearance during suspension compression. The Flowmaster performance Y-pipe shown provides a maximized and smooth transition similar to a header collector from the 2-inch leader pipes to the 3-inch outlet.

V-8 Ignition

Early Jeep V-8s, including the I-6, used a points system until 1976 and the Motorcraft electronic ignition system until 1986. The Motorcraft system worked well but was prone to sudden failure without warning. Many Jeep owners made it a regular habit to carry a spare ignition module in case of a failure. The HEI system is considered the most reliable classic ignition system and only requires a single wire for power. As was discussed in the I-6 section, a GM HEI-style distributor can be adapted to work in the V-8 with only a gear modification. These conversion distributors can be found ready to go and are easy to install.

Davis Unified Ignition (DUI) makes a top-of-the-line HEI-style distributor for the Jeep V-8 that provides the ultimate in ignition performance.

Along with the performance distributor, a matched set of spark plugs and a performance set of spark plug wires from a company such as DUI, LiveWires, or Accel complete the ignition system upgrades. Spark plug gap should be set according to the distributor manufacturer. Popular performance spark plug manufacturers are E3, NGK, and Champion.

Converting to a GM-style HEI distributor increases spark performance and reliability. Davis Unified Ignition makes a ready-to-install premium version of the HEI conversion distributors.

LiveWires spark plug wires offer excellent HEI performance along with a mesh shield surrounding the wire to aid in protecting the wires from heat, wear, and objects. LiveWires are available in pre-made lengths for an HEI conversion on both the I-6 and V-8.

AMC V-8 HEI Installation

Installation of an HEI distributor is not a difficult job and can be done in an hour or two.

Begin by noting the No. 1 plug wire on the distributor then remove the stock plug wires and distributor cap, and pull the vacuum advance hose.

Locate the engine at top dead center (TDC) by removing the No. 1 spark plug and cover the hole with a finger. Rotate the engine in short starter bursts and feel for pressure on the finger from the compression stroke. Observe the distributor; the rotor should be at the location noted for the No. 1 plug wire. Look for the timing mark on the engine balancer, and rotate the engine to line up the mark with the timing-gauge “0” mark. This is TDC.

1 From 1973 until 1980, the AMC V-8 was equipped with the Duraspark electronic ignition system. This system used a separate coil and electronic control module. The Duraspark modules were famous for sudden failures and could render a Jeep dead in the water. Most Jeep owners carried a spare module.

2 After getting the engine positioned at TDC, find a location to make a mark to note the position of the rotor. This aids in installation of the new distributor and hitting the proper location. A piece of tape with a mark on the coolant bypass hose is an excellent location.

3 The distributor hold-down is located below the distributor at the top of the timing chain/water pump housing. Loosen the bolt and remove the hold-down.

4 After the distributor wiring plugs are disconnected, remove the distributor by pulling it up from the engine. The rotor rotates slightly with the gear splines. Be careful not to allow dirt or items to fall into the distributor hole.

5 A side-by-side comparison of HEI and Duraspark distributors. The HEI (left) uses a much larger cap that integrates the ignition coil for less loss.

6 The old Duraspark module and its wiring can be removed and no longer used. The original wiring harness has a positive lead (usually a larger red or yellow wire) that should be marked and set aside for reuse with the new distributor.

7 Like the module, the original coil and its wiring may be removed if no longer needed. The HEI coil is capable of higher output, allowing for increased spark plug gaps, resulting in a hotter ignition and larger spark area.

8 The oil pump shaft is driven by the end of the distributor and can be seen deep within the distributor’s mount hole. It may be necessary to rotate the shaft slightly with a screwdriver to line it up with the new distributor.

9 Install the distributor in the engine, aligning the rotor in the same position as the old one that was removed. In most engines, including the AMC V-8, this aligns the key at the bottom of the distributor gear with the oil pump drive rod, allowing the distributor to drop fully in. Rotating the engine with the distributor partially installed also allows it to drop in place. In this case, place the engine back at TDC before continuing. Replace the hold-down and lightly tighten.

10 Install the HEI cap, tighten the clamps, and connect the distributor wiring harness to the cap. The HEI cap requires new spark plug wires. LiveWires spark plug wires are available for the HEI system in an AMC V-8. These wires are available in several colors and feature a protective outer mesh cover. Install the wires starting from the No. 1 position and following the 1-8-4-3-6-5-7-2 firing order.

11 With the distributor installed and lightly clamped in place, move on to getting power to the HEI. The beauty of the HEI is its integrated design, requiring only switched battery power to operate. No harness, no ignition coil wire, no mess. One of the two harness connectors that were unplugged from the old factory ignition module has a large red or yellow wire, which is the switched power source. Connect this wire to the BAT terminal in the cap of the new HEI distributor.

12 Although (technically) the distributor just needs one switched power battery wire on many AMC-era CJs, the wire from the Duraspark harness makes for hard starting due to its power being momentarily cut off during engine cranking. The Jeep’s wiring causes certain circuits to cut off during cranking to allow full power to the starter. The fix for this is using the existing starter solenoid’s bypass circuit, which is engaged during cranking, providing full power to the distributor. Splice a lead from the terminal labeled “I” into the switched power wire to the distributor.

13 The HEI delivers a higher energy spark to the spark plugs, and increasing plug gap increases ignition speed and efficiency. Most HEI systems recommend setting the plug gap at .035 to .055 inch. Using a plug gap gauge sets the gap correctly. Installing new plugs is probably a good idea but not needed unless the original plugs are old and worn.

14 Adjusting the timing is becoming a lost art form, and timing lights are becoming a thing of the past. After installing new plug wires and reconnecting the battery, attach the timing light and, with the vacuum advance hose to the distributor disconnected and plugged, start the engine. Use the timing light to observe the location of the timing mark on the harmonic balancer. Rotate the distributor to adjust to 5 degrees; when proper timing is achieved, tighten the distributor bracket.

Fine Tuning the Timing

After initial timing is set and everything is in its place, drive the Jeep, running the engine normally then make several hard acceleration runs, from both a stop and a passing style. Note the engine performance and adjust the timing if the engine seems sluggish, pings, or is hard to start. Without a timing tape on the balancer to read the exact timing, a little experimentation will find the proper timing.

Sluggish, poor performance is often a case of the timing not being advanced enough. Rotating the distributor clockwise to advance will improve performance. Do this in small intervals, followed by a driving test. If the engine shows signs of pre-ignition (pinging) or is difficult to start, the timing is likely advanced too far. Rotating backward followed by a driving test will help you to find the optimum spot.

Additional Performance Parts and Modifications

Some general performance modifications and parts are nearly universal across many engine types.

Air Filters

Reusable air filters such as ones made by K&N, AFE, and Airaid provide better filtering while increasing airflow. Driving a Jeep in off-road conditions exposes the air filter to dirtier conditions than street driving alone. Cleaning these filters more frequently ensures peak performance and longevity. For extra protection, installing a K&N pre-cleaner wrap around the air cleaner keeps larger debris off the filter element.

K&N set the standard for non-paper air filters. These filters use a gauze type material coated with a special oil to remove contaminants from air entering the engine while improving airflow. These reusable filters come in many sizes and styles.

Snorkels

Some Jeep owners install a snorkel system to prevent water from entering the engine. No direct bolt-in snorkel systems are currently available for the CJ and most are fabricated using a matching air intake plenum combined with some creative plumbing to either move the air cleaner to the outside of the Jeep at a high location, such as the windshield, or plumbing into the inside area of the Jeep’s cowl.

The interior helps keep water out when fording streams, but driving through deep water may still submerge the filter. Hydrolock is a condition experienced when water enters the engine. Because water does not compress, the engine stops rotation until the water is drained, usually from the spark plug holes.

A snorkel alone is only half the equation for crossing deep water. The exhaust system should be routed to allow the engine to push out exhaust when underwater. Relying on the exhaust pressure when crossing deep water can cause excess pressure in the engine, resulting in stalling. A sudden change in pressure can cause the water to back up into the exhaust and end up within the engine’s cylinders.

Cooling

A Jeep’s cooling system is subjected to harsh conditions off-road. Slow speeds drive up underhood temperatures, and trail debris such as dirt, rocks, and mud can end up in the radiator fins, potentially causing overheating. A factory Jeep radiator can be upgraded to a more modern aluminum radiator for increased cooling efficiency.

Novak Conversions makes a direct fit aluminum radiator for the CJ. In addition, a large factory-style engine-driven fan or electric fans running with a proper shroud are needed to pull enough air through the radiator.

The traditional style but increased capacity four-core radiator combined with a factory fan shroud and large engine-driven fan keeps my AMC 360 cool even on the hottest days on the trail. Good airflow and high-capacity systems are put to the test in Jeeps used off-road.

Flex-a-Lite makes a direct-fit, shrouded dual-fan system for the CJ. Note that these fans draw 19.5 amps, which can put a heavy load on a stock electrical system. A higher output alternator may be needed. Small flex-style performance engine-driven fans are typically insufficient for off-road use and should be avoided.

An old-school Jeep trick to help with underhood temperatures is the installation of 1/2- to 1-inch-thick blocks under the cowl side of the Jeep’s hood hinges. This props the rear of the hood up, creating a nearly full-width vent that can drastically remove engine heat. The functional look created by this is rather unique and can be a conversation piece to the novice.

Some companies such as Royal Purple and Lucas make coolant additive to help increase cooling efficiency. There has been mixed reviews on the effectiveness of these products. If cooling problems are experienced, it may be worth a try.

An old trail trick to keep the underhood temperatures down was to stick a block of wood or steel under the cowl side of the hood hinges. The 1/2-inch or so opened a gap that ran fully across that allowed underhood heat to escape. Slow trail driving drastically raises underhood temperatures; even placing your hand there allows you to feel the heat moving.

Finally, using a quality water pump with a proper pulley configuration is another important component to cooling in a Jeep. Spending some extra money in the area of cooling only lowers the likelihood of trail-related cooling issues.

PCV, Idle Mixture and Timing

The positive crankcase ventilation, or PCV, valve is designed to remove vapors from the inside of the engine. Most PCV valves draw engine vapors into the induction system to be burned with the fuel mixture. An old or defective PCV valve can hinder engine performance and cause excess vapor buildup within the engine.

Some carburetors and injection systems do not have provisions for adjusting idle mixtures but, if possible, adjust the idle mixture to proper specifications. A vacuum gauge is often the best device for adjusting the mix. Improper mixture, especially off-road, potentially causes the engine to run hot or have an excess fuel smell. An over-rich condition fouls spark plugs and leaves soot deposits in the exhaust system.

Proper engine timing affects many variables, including engine longevity, fuel economy, and engine power. Setting timing is a simple process using a timing light with the engine running. Rotating the distributor advances or retards the timing as needed.

Oil and Fuel Additives and Ethanol

Old Jeep engines have been left behind in the modern world. Most gasoline is unleaded and contains a mixture of ethanol. The early AMC era used engines designed to use the lead in gasoline to lubricate valveguides and piston rings. The removal of lead and the addition of ethanol can sometimes cause issues. Lead substitutes can be added to the fuel to slow wear.

In recent years, zinc dialkyl dithiophosphate (ZDDP), a zinc-based additive found in engine oil, has disappeared from most brands. This oil component provided protection against wear for older engines, especially in a flat-tappet camshaft. Most newer engines use roller camshafts and other modern components that do not require ZDDP. It is claimed that adding a ZDDP additive such as Lucas Break In Additive replaces the missing ZDDP and prevents wear in old engines run without ZDDP.

Determining the effect of ethanol mixed into gasoline used in an old engine can make your head spin from the possibilities. Some older engines run normally; others experience performance and fuel-efficiency issues. Finding non-ethanol gasoline is becoming more difficult and there are other ways of making your Jeep’s engine more tolerant of the mixed gas.

Most aftermarket carburetors perform well with mixed fuel and can be adjusted using mixture screws and jet changes. Both stock and aftermarket TBI and EFI injection systems typically perform well with mixed fuel, especially more advanced systems that run oxygen and MAP sensors.

Pretty, Shiny Stuff

Why not finish off your Jeep’s underhood with some items to show off your hard work? A set of aluminum or chrome valvecovers and a matching air cleaner dress up the engine a bit. Degreasing the engine helps keep the engine cool and prevents the possibility of the gunk smoking or catching fire from the heat. Once the engine is clean, a fresh coat of engine paint can finish the package.

Putting It All Together

Starting with the engine, I put together a recipe for a Jeep suited for maximum performance on- and off-road. As stated earlier, the factory engines provide for the Jeep in this capacity quite well. Retaining the factory engine, if possible, saves money and allows for upgrades to increase performance.

Based on that premise, this factory I-6 Jeep engine is equipped with the following.

• Aftermarket intake with a Weber carburetor or TBI

• Set of 3-into-1 dual-exit headers

• Performance Y-pipe running through a 2½-inch exhaust and a performance muffler

• HEI-style distributor, preferably a brand name or a conversion

• Set of performance spark plug wires and spark plugs

• Reusable air filter

• Factory-style engine-driven fan with a proper shroud

Based on that premise, this factory V-8 Jeep engine would be equipped with the following.

• Matched aftermarket intake and camshaft combination

• Off-road-friendly carburetor

• Set of factory exhaust manifolds feeding into a performance Y-pipe

• 3-inch single exhaust with a performance muffler

• HEI-style distributor, preferably a brand name or conversion

• Set of performance spark plug wires and spark plugs

• Reusable air filter

• Factory-style engine-driven fan with a proper shroud or a proper-size electric fan setup

Many of these elements would work well with a swapped engine, with the exception of a modern fuel-injected engine. Modern engines would likely not need any modifications because their out-of-the-box performance specifications are well suited for the Jeep.

Adding some pretty stuff to an engine, such as a nice set of aluminum valvecovers and an attractive air cleaner, cleans up the underhood look. Of course, a trail-used Jeep’s engine does not stay clean for long unless it’s cleaned regularly. This restored Jeep has an engine bay that you could eat off. It’s nice to look at but isn’t practical for the trails.

This modified I-6 provides loads of low-end torque perfect for both on- and off-road driving. The simple setup is easy to maintain and repair, if needed. Specs for the engine include a 258-ci I-6, Clifford manifold and header, Howell TBI, TFI ignition conversion, and Omix-ADA valvecover.

An AMC V-8 has no problem powering a CJ and performance modifications always add to the package. This factory-304-equipped CJ-7 runs that Edelbrock Performer Series combination that works so well. The Holley carb, intake, and cam combination result in extra-low-end torque and mid-range horsepower, which are well suited for an on- and off-road Jeep. The in-frame Hedman headers, dual exhaust, and HEI distributor finish the engine.