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