Jim Smart
October 14, 2005

In the beginning, the 4.6 SOHC was equipped with a plastic intake manifold with an aluminum throttle body. With its long runners, this manifold helped the SOHC make good low- to mid-range torque. But it didn't set the world on fire in terms of real world power. For made this intake manifold out of plastic to keep the intake charge cooler. This manifold coincides with the early round-port heads used from 1991-'98. The '99-and-up PI heads use a different intake manifold designed for the PI ports.

One solid option for SOHC builders is the Ford Racing Performance Parts intake manifold that was introduced in 1998. This cast-aluminum manifold has long intake runners for a good combination of mid- and high-rpm torque. Instead of the single throttle body we see with most SOHC engines, the FRPP manifold has a twin-bore throttle body for increased air-flow. In 2001, Ford introduced a similar intake manifold for the Bullitt Mustang GT. Where it differs is its compatibility with the '99-and-up PI head. The earlier FRPP manifold will not work with the '99-and-up PI head.

Aftermarket cast-aluminum manifolds are available for the SOHC engines now. The downside to the stock plastic manifold is the inability to modify it in any way for improved performance, and its penchant for cracking with age or boosted environments.

The DOHC induction system is a two-port design where we operate on one primary intake port in normal driving, and open a series of secondary ports when the throttle is wide open. This is performed with an Intake Manifold Runner Control system (IMRC) that opens when the pedal hits the metal.

The '93-'98 Lincoln Mark VIII induction system had a twin-port design, where the primary intake port was different than the secondary intake port. This is likely the worst intake manifold you can use on top of a 4.6 DOHC engine because the intake runners are too small for high-rpm use.

If you have the early DOHC heads, you may opt for the '96-'98 Mustang Cobra intake manifold, a cast-aluminum affair with larger intake runners for improved breathing. It comes on stronger at high rpm. Not only are the runners larger, they are longer for improved low-end torque. When you mix in the improved IMRC, which is designed to come on at 3,200 rpm, this improves performance to some degree. There were actually two types of Cobra manifolds in 1998: plastic and aluminum. Opt for the cast manifold.

For those of you using the '99-and-up Tumble Port head, you need to use the appropriate intake manifold, also different from '99-and-up. If you happen to be running the super-rare '00 Cobra R head, you will need the Cobra R manifold as well.

Ignition System
The Modular V-8s have always had distributorless, computer-controlled ignition systems. From 1991-'98, they employed two coils packs--one located on each bank. The computer fires the spark plugs in pairs, with two spark plugs fired at the same time, but not igniting a fuel/air mix at the same time. This is known as a waste-spark system, where the computer's four channels fire two plugs at a time: one on compression-ignition stroke and the other on exhaust stroke. In 1999, Ford went to an eight-channel "coil-on-plug" ignition system, with each spark plug having its own ignition coil. This completely eliminates the ignition harness. With twin coil-pack ignition systems, each coil has four terminals to fire four spark plugs, with two of the terminals fired at a time in the four-channel systems.

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