Dale Amy
January 1, 2009
With the rotor package removed from the GT500's Eaton blower, PHP's Karl Roekle smoothes and subtly reshapes the inlet area. This is one of the more labor-intensive aspects of the $1,499 Paul's High Performance Stage 3 Shelby upgrade package.

Horse Sense: The Stage 3 name suggests there might be other stages as well. Stage 1 ($775) consists of the PHP tune on the SCT flash tool, along with the cold-air kit. PHP's Stage 2 kit ($975) adds a 2.6-inch blower pulley (and compensating idler) and a 160-degree thermostat to the Stage 1's inclusions.

Few would argue that the Shelby GT500 is a performance animal right off the showroom floor, as you might well expect from the most powerful-and most expensive-Mustang ever factory assembled. But as we've seen time and time again, the S197 Snake's factory-rated 500 flywheel horsepower is really just the starting point of this thing's venomous potential. Highly effective (but not inexpensive) mods include swapping on a larger, more efficient blower from Ford Racing, Kenne Bell, or Whipple, but not everyone may be inclined to toss out their perfectly good OEM, hybrid-Roots Eaton supercharger just yet. If you find yourself in this latter group, we suggest the Stage 3 performance upgrade package from Paul's High Performance.

Mightily effective, as our dyno results show, the Stage 3 upgrade starts with some careful hand-grinding on the air-inlet side. You can either ship your Shelby's throttle body, blower inlet elbow, and the supercharger itself to PHP to have them internally reshaped, smoothed, and returned to you, or simply swap those components on an exchange basis for ones that have already received the porting treatment.

But the Stage 3 kit doesn't stop there. It also includes a smaller blower pulley installation for increased boost, along with a revised idler pulley so the factory serpentine belt can be retained. A 160-degree thermostat, PHP cold-air kit, and razor-sharp PHP custom tune loaded on an SCT X3 PowerFlash handheld programming tool round out the package.