Richard Holdener
December 1, 2008

Step By Step

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Mmfp_0812_07_z Psi_boost 2003_cobra_20_psi
KB SC '03 Cobra-20 PSIGiven its humble beginnings of something near 360 rwhp, it's amazing to see this Terminator motor thumping out nearly twice that power level all from a simple blower upgrade. Terminator owners should give thanks for Ford's decision to go the forced-induction route rather than increasing displacement. Running 20 psi of boost, the Kenne Bell supercharged 4.6L Cobra motor thumped out 702 rwhp and 578 lb-ft of torque. In true positive-displacement form, torque production from the supercharged motor exceeded 500 lb-ft from as low as 2,400 rpm all the way to our self-imposed rev limit of 6,700 rpm. The power curve was still headed up at 6,700 rpm, so we know there was more power to be had from this combination.
Mmfp_0812_08_z Psi_boost Kenne_bell_supercharger
All three motors were equipped with the new Kenne Bell 2.8L H-series twin-screw supercharger. Capable of supporting well over 1,000 hp, the H-series 2.8L blower was the perfect candidate for this high-boost test.
Mmfp_0812_09_z Psi_boost Discharge_port
The secret to the elevated efficiency of the H-series blower is the discharge port. The port timing (how the air exits the blower) helps determine the charge temperature and overall flow. Kenne Bell did a ton of research and development to come up with the new H-series (high-boost) blower designs.

Naturally, all three kits featured air-to-water intercooling, so the idea was to run the same blower, intake manifold (into the blower), and free-fl owing induction system to eliminate any inlet restrictions. All three applications were also treated to the necessary fuel-system upgrades to provide the requisite fuel for the given power level. To level the playing field, naturally each combination was tuned to provide the same air/fuel and timing values. It should be noted that all three were also equipped with Bassani after-cat exhaust systems. With everything in place, all we had to do was crank up the boost and compare the results.

'03-'04 4.6L Terminator
702 HP at 6,700 RPM
578 LB-FT of Torque at 4,900 RPM
Pulley Combination 7.5 Crank/3.25 Blower (2.30 Drive Ratio)
When first introduced in 1996, the Four-Valve Cobra was welcomed with open arms by Mustang enthusiasts, who saw the DOHC motor as the weapon of choice to do battle with the 5.7L Camaros of the world. As is usually the case, the performance world marched on and quickly left the 300hp Cobra motor in its wake. Ford soldiered on with other normally aspirated Four-Valve motors, which received a power upgrade in 1999, but it wasn't enough to combat the larger and more powerful LS1 motors offered by the General.

What Ford needed was a serious power player; unfortunately, the modular-motor configuration suffered from narrow bore spacing that limited the eventual bore diameter, which in turn, limited the displacement. It was possible to improve the displacement via an increase in stroke length, but even with the additional stroke, 5.0 liters seemed to be the absolute usable limit for a production Four-Valve Cobra motor. Even if Ford decided back then to offer a 5.0 mod motor, would it have been enough to do battle with a 400hp 6.0L LS2?

We now know that Ford never increased the displacement of the Cobra motor (though look for just such a change in 2010); instead it went the forced-induction route. This decision forever changed the lives of many Cobra owners, as the choice of boost over displacement not only increased the factory power output well beyond anything that was possible in normally aspirated trim, but it also offered up a license to produce unlimited street/track horsepower.

Introduced in 2003, the now-legendary Terminator motor offered an exceptional peak power output (underrated at 390 hp), but more importantly, something that was sorely missing in any previous modular motor application, something we like to call torque. Not surprisingly, the normally aspirated Four-Valve motors were somewhat peaky, offering plenty of high-rpm power (especially in modified form), but they lacked the torque production to compete with the larger 5.7L and 6.0L motors over at the Chevy camp. The presence of boost pressure literally transformed the mod motor. The instantaneous boost and attending torque production felt like someone stuffed a 460 underhood. In this case, boost was the perfect replacement for displacement.

The Terminator motors installed in the '03-'04 Cobras were, and continue to be, impressive performers. Compared at 3,000 rpm, a stock supercharged Cobra motor might offer as much as an extra 150 lb-ft of torque over the N/A motor. It's this abundance of torque that pushed the Cobra into a real-world competition with the Corvette. Even more importantly for enthusiasts, Ford built the '03-'04 Cobra motors to withstand plenty of abuse. As good as the Terminator motors are in stock trim, it's the way they respond to modifications that really sets them apart from lesser combinations. Adding 50 hp, 75 hp, or even 100 hp or more to an '03-'04 Cobra motor is as easy as adding an air intake, blower pulley, and performance tune.