2008 Ford Shelby GT500 Exhaust Test - Now We're Kookin'

Here's a comparative look at the Kooks header (top) and the factory's restrictive cast-iron exhaust manifold. The 304-grade, stainless-steel headers feature primaries measuring 1 3/4x3-inch and Kooks' patented Velocity Spike merge collector. Kooks also offers the headers with 1 7/8x3-inch primaries, for Shelbys that make more than 700 hp.

Note the difference between the OEM exhaust gasket (top) and the gasket that's provided with Kooks' header system. While the stock gaskets have a two-piece design, Kooks uses a longer, one-piece seal for mating header flanges to the cylinder heads. It's important to make sure the cylinder heads exhaust-port surfaces are thoroughly scraped clean before installing the new gaskets or reusing the OEM seals.

Saul fits the passenger-side header in place first, followed by the driver-side tubes. As long as there's sufficient clearance, laying the headers up is the easy part and can be done in either order...

...Securing the fasteners is a whole other story. Ford uses studs to install Shelby manifolds. The Kooks headers are fastened with 13mm bolts, which must be treated with a dab of antiseize before tightening them in the heads.

It's actually too bad that this exhaust system sits below a Mustang and out of sight. Kooks' mandrel-bent, stainless tubes look great and are designed for clean fitment on a Shelby. The system we installed includes the aforementioned headers (PN 6027; $997.36), along with a 3-inch catted X-shaped crossover (PN 6028-CX; $566.61) and a pair of 2 1/2-inch stainless mufflers and mid-tubes (PN 6030; $750), which are also applicable on Three-Valve Mustang GTs.

From up top, the stainless headers fit without any conflict with steering equipment, engine mounts, or the chassis on either side, and they look much better than the unfinished, plain cast-iron pieces that come with new Mustangs.

This is a look inside the Kooks' metallic substrate cats that are part of the long-tube system we installed. The element inside the smaller (diameter and length) Kooks cats is a lot less restrictive than OEM converters, which is important for supercharged applications.

There's literally nothing inside Kooks' stainless-steel, 2 1/2-inch mufflers to challenge or obstruct exiting exhaust gasses.

Here it is, from front-to-back-Kooks' Shelby GT500 long-tube header system.

Once all of the pieces are in place, Sean's ride is lowered back to Earth and affixed to the chassis dyno...

...where we'll see what type of difference long-tubes make on a big-boosted Shelby.