2006 Roush Stage 3 Mustang

We've reached a crossroads. Factory-offered performance packages, such as the GT500 and Z06, are becoming so good they meet (or exceed) the performance levels of many tuner cars.

So it's no surprise that Roush, a name long associated with racing and performance, offers a variety of tuner packages for the Ford Mustang, F-150, and even its micro Focus. The new 5.4-liter GT500 offers a trove of performance hardware, but it's a limited-production vehicle most Mustang fans will never own. If you have a 4.6-liter Mustang GT, Roush's performance upgrades deliver GT500-like results-despite remaining nearly one liter smaller in displacement than the GT500.

We tested Roush's midlevel power package known as the Stage 3 ($21,000), the heart of which is a "ROUSHcharged" Roots-type supercharger that inflates the cylinders with 5psi worth of atmosphere. An air-to-water intercooler setup helps the supercharger keep its cool so it can deliver consistent performance. A high-flow air filter lets cool air in, while Roush's mandrel-bent 2.25-inch dual exhaust system lets hot air out. A specially programmed computer enables the Stage 3 engine to crank 415 horses (115 over stock) on normal pump fuel.

Around town the Stage 3 engine is docile. Crack open the throttle, and the supercharger comes alive, the exhaust roars, and the rear tires spin as if slathered in Crisco. Smoking the skinny factory 235/55ZR17 all-season treads is easy, but Roush does the deed wearing huge 275/40ZR18 BFGoodrich g-Force T/A KD tires that pair with Roush's massive 18x10-inch forged-aluminum, chrome-plated five-spoke wheels.

To help the tires remain connected to tarmac, the Stage 3 uses special front struts, one-inch-lower/35-percent-stiffer springs, larger front/rear anti-roll bars, upgraded bushings, and Roush's custom rear Panhard rod. In handling tests, the setup delivered a noticeable improvement in cornering and max lateral acceleration. However, get too greedy with the throttle in a corner, and the 415 horses will zip the rearend out. To help keep speed in check, Roush fits the Stage 3 with custom four-piston brake calipers that clamp big 14-inch-diameter vented rotors to stop the Stage 3 14 feet shorter than a stock GT.

Roush further ponies up with its seven-piece Aerobody Kit, lower valence foglights, racing stripes, and Roush emblems. The interior features embroidered sport leather seats, a special white-face gauge cluster, Roush pedals, and Roush-embossed floormats. While the interior is comfortable for all, the driver seat remains the best seat in the house.