When offered the chance to start up Project 997 TT, I jumped all over it. No, it's not my car and yes, I'm still enjoying my soon-to-be-slow-by-comparison Project M3. So let's get right to it.

One of the most popular Turbo upgrades is a new exhaust system. These flat-six motors have a unique tone, so who could blame owners for wanting to exploit that? And on a turbo-charged car, substantial horsepower gains can be had. To prove it, we contacted Fabspeed for its turbo-back exhaust system.Fabspeed's exhaust system for the 997 twin turbo is T304 stainless steel, complies (reportedly) with the original Porsche factory warranty, and is 50-state legal. It's offered in three different sound levels. We chose the quietest. With a change to high-flow catalytic converters and freer-flowing canisters (the 30-plus pound loss in weight is nice too), we expect significant gains. At $3,700, plus the optional $850 tips, there ought to be.

To plot accurate horsepower improvements, we must baseline the car first. Enter Imagine Auto of Lenexa, Kansas, the tuning and dyno facility we will use for our Project 997 TT testing, and official installer for this project. Its Mustang 500 SE dynamometer tests all driveline configurations and has a feature to simulate real-world engine loads for proper tuning. The company also specializes in Porsches. You may remember we recently featured two of IA's supercharged Boxsters and the owner's monster 996 Twin Turbo (ec, February and March '07).

Even though we could disconnect the front drive axles and test in rear-wheel-drive mode, all our testing will be done in all-wheel-drive mode for all-wheel horsepower (AWHP). IA usually reports a consistent five percent extra loss to the wheels when testing in all-wheel-drive mode, compared to testing for rear-wheel horsepower. Additionally, we'll be testing the car in overboost mode, a factory option that adds an extra 3 psi boost for up to 10 seconds at a time, but only up to 5500 rpm-thus affecting peak torque but not peak horsepower.

On the dyno, Project 997 TT shows a phenomenal powerband. Thanks to the new variable turbine geometry (VTG) technology, the turbos push the 3.6-liter engine's output to 300 lb-ft of torque at an astonishingly low 2800 rpm, which increases to a 440 lb-ft peak at 4000 rpm, never dropping below 350 all the way to redline. That adds up to 350 AWHP by just 4200 rpm and 429 peak AWHP at 6100 rpm. Such is the beauty of larger-displacement turbo engines-there's power everywhere. This is going to be fun.

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