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.

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As noted, the only performance modification to Jeff Schmell's '08 GT500 at the time of baseline testing was a manifold-back, 3-inch, off-road exhaust system (yes, it's going be a drag car.) This likely skewed both the before and after numbers upwards slightly, but the difference between the two-the delta-should still be representative. On that basis, PHP's Stage 3 upgrade certainly shows its worth. Note that torque is up after the upgrade by three digits from a just-off-idle 1,100 rpm, while the horsepower delta is more linear, peaking at a whopping 195 rwhp higher at 6,300 revs. A good bang for the buck, we say.

For the Shelby, 3-inch exhaust systems have become common-and fairly logical. PHP offers such systems from no less than three or four manufacturers. While the main advantage is the power gained from reduced restriction (roughly 12 rwhp and similar torque for a after-cat system), a secondary benefit is a significant reduction in exhaust system heat, according to PHP boss Paul Svinicki. But be realistic: A 3-inch system is undoubtedly loud, maybe overly so to some ears. We can say without hesitation that the cat-free, 3-inch system on Jeff Schmell's car is not one we'd want to listen to on a cross-country-or even cross-county-tour.

Help may be on the way, however. As we write this, PHP has just received a set of 3-inch mufflers from Bassani that are said to be notably quieter than most on the market. Paul has yet to strap them on for testing, but you may want to consider them to keep the decibels down inside your GT500's cockpit.