2003 Ford Mustang Cobra Increases Power - Mods For Mods Part 1

In four previous issues of MM&FF (June-August 2004), we took a hard look at the performance modifications available for the two-valve 4.6 GT motors. Heck, we covered everything from simple throttle bodies and elbows (both NA and supercharged) to nitrous and blowers. Along the way we managed to sneak in ported cylinder heads, a variety of different cam profiles and even the effect of changes in compression ratio.

All in all, we'd say the "Mods for Mods" series offered pretty extensive performance coverage for the two-valve Modular V-8. Having nearly exhausted the available bolt-ons and buildups for the two-valve GT motors, it was only logical that we turn our attention to the more performance-oriented four-valve Cobra motors. As luck would have it (it is amazing what the right amount of begging and pleading can do), we managed to secure the mother of all four-valve 4.6 test motors--an '03 Cobra crate motor assembly. Talk about the ultimate four-valve test mule!

The beauty of the Cobra engine is that in addition to every nut and bolt being brand-spanking new, it is factory equipped with a number of desirable features, not the least of which is a hefty chunk of forced induction in the form of an Eaton (positive displacement) supercharger. While the presence of the supercharger is cause enough for celebration, the real key to the success of the '03 Cobra plant from Ford Racing is that it was configured from the factory to accept the rigors of supercharging. This means desirable (for forced induction) low-compression, free-flowing four-valve heads and even an efficient air-to-water intercooler to help lower the inlet charge temperature to suppress detonation. Having seen blown '03-04 Cobras already exceed 700-wheel hp, naturally we were anxious to get started with the modifications. In future "Mods for 4V Mods," look for testing on cams, ported cylinder heads and even a four-way forced induction shootout, but for part one, we will stick with some basic bolt-ons, including tuning the air/fuel and timing curves, inlet and exhaust modifications and the always popular increase in boost pressure via changes to the drive ratio.

The first order of business was to get the 4.6 installed on the engine dyno. While '03-04 Cobras have been run extensively on the chassis dyno, not many supercharged four-valve motors have found their way onto the engine dyno. The assembly from Ford Racing was shipped complete, including the serpentine drive assemblies (both blower and accessory). Since we planned on running the F.A.S.T. stand-alone engine management system, we removed a number of factory components that were unnecessary: the clutch and pressure plate to facilitate mounting the motor, plumbed water to and from the air-to-water intercooler and capped the necessary coolant and vacuum lines.

Just as with the two-valve 4.6s, the F.A.S.T. engine management system allowed us to delete the factory mass-air meter and attending inlet tubing. All that was necessary was the stock throttle body and inlet into the blower, something we would be upgrading later during testing. Though the Ford Racing Cobra mill was originally equipped with a coil-on-plug ignition system, we replaced the factory ignition with the coil-pack system used previously on the 4.6 GT motor. This in no way changed the power potential; it simply allowed us to use an existing management system on the four-valve V-8.

After hooking up the F.A.S.T. system, we dialed in the factory air/fuel and timing curves, which were supplied by Kenne Bell. With all its chip expertise, it knew not only what the factory timing curve (at WOT) should look like, but what the force-fed Ford would tolerate on the 91-octane California pump swill we planned on running. The idea was to run with the factory timing values (using the F.A.S.T.) then tune for additional power. Initially, we planned on running the Ford Racing crate motor with the supplied serpentine belt driving all of the accessories. With no power steering reservoir or lines to hook up a simple loop system (to lubricate the pump while in operation), we eventually decided to forgo the accessories and install a Meziere electric water pump. This allowed us to eliminate all of the accessories (with the exception of the alternator) while retaining the drive system for the blower.

The Cobra crate motor was shipped with the factory (cast iron) exhaust manifolds. We planned on replacing these with a set of headers, but to test the power gains offered by the Hooker (Flow Tech) long-tube headers, we needed to hook up a free-flowing exhaust system. The dyno exhaust consisted of a pair of 2.5-inch tubes run with no mufflers. We did not want to restrict the exhaust system with cats or mufflers.

After replacing the stock Cobra injectors with a set of 65-pounders (the rating was fine for our intended power level, but the F.A.S.T. harness was configured to accept the early style injectors) we were ready to rock. On hand for testing on the '03 Cobra motor was an Accufab throttle body and inlet, a set of Flow Tech headers, the tuning from the F.A.S.T. system and an array of blower and crank pulleys from South Florida Pulley Headquarters to increase the boost pressure supplied by the Eaton supercharger.