The Eaton
Testing opened with the totally stock Mustang--meaning the standard 31/2-inch blower pulley and nominal 8 pounds of boost, along with a totally stock air path from air filter to tailpipes. As the Cobra warmed up on the dyno, we once again marveled at how smooth the engine was. Clearly Ford has sent its newest engines to finishing school.
The rear-wheel horsepower came out at 375 hp. This is notably higher than expected from Ford's 390 flywheel horsepower rating, but it wasn't surprising given how fast '03 Cobras have been running at the drag strip. Obviously Ford has been underrating the Cobra engine.
Next we tried the smaller 3-inch "Lightning" supercharger pulley, which has already proven a popular '03 Cobra upgrade. This is the pulley used on the 5.4 Lightning pickup, which also uses this same Eaton blower, but mated to somewhat slower engine rpm.
Changing the Eaton pulley is difficult. It can either be done by swapping entire blower drive ("nose") sections, or using a special puller to drag the pulley off the input shaft. The pulley is lightly built, and it uses only a taper fit on the blower input shaft for grip. There is no keyway or other locking device, therefore the force involved in this pressed-on pulley is rather high. Kenne Bell has found most puller attempts resulted in damaged pulleys and broken power steering pump pullers, so they prefer to change entire blower nose sections. However, we had a Performance & Diesel Innovations puller, so that was used along with PDI's 3-inch pulley.
Boost jumped to 13 pounds and power to 417 hp. Remember, this is through the stock air filter and exhaust, so even with a simple pulley change, there is good power to be had. Also, the spark and fuel were well within limits with just the pulley change, so no electronic changes were required at this level. However, as the 3-inch pulley takes the Eaton blower to high speeds (it was at 16,250 rotor rpm at 6,500 engine rpm on the Cobra), and its efficiency was clearly waning, no more boost increases via smaller pulleys were attempted.