Richard Holdener
April 24, 2007

The twin-turbo system from HP offered only slightly more boost pressure at 2,500 rpm than the centrifugal (3.7 vs 1.9 psi), but was well down on the 12.3 psi supplied by the Eaton. That difference in boost pressure translated into a torque deficiency of 160 lb-ft. The turbo lagged behind the Roots blower until 3,900 rpm at which point it took off with a vengeance. Running a maximum boost pressure of 13.6 psi, the HP turbo system eventually produced an amazing 830 hp and 756 lb-ft of torque. Imagine, the turbo system bested the peak torque production of the twin-screw and the peak horsepower production of the centrifugal by a country mile. Anytime you can produce an extra 100 hp and 150 lb-ft of torque at a similar boost reading, you know you've down something right.

Of course, all that extra efficiency comes with a penalty of low-speed torque (at least compared to the positive displacement blowers). Were we running the turbos at just 11 or 14 psi, we probably would have selected the smaller 46mm units (or better yet, an electronic waste gate controller) to further improve turbo response and the attending low-speed torque production. Of course, if you are looking to top 900 hp (something we did at just 17 psi with the HP system), these 57mm turbos are the hot setup.

This cast-aluminum discharge tube assembly was designed to connect the T-Trim Vortech to the throttle body. Note the compressor bypass valve designed to eliminate pressure surges in the intake during cruise and lift-throttle conditions.

There you have it, the ultimate boost bash. Now all you have to do is look over the attending graphs and choose the system that best meets your needs. For some, the factory Eaton will forever power their four-valve Cobra. It's hard to argue with the immediate boost (and torque) response of the Roots design. With plenty of aftermarket support for the '03-04 Cobras, extra power is just a phone call and Visa number away. Of course, there is a limit to the power available with the Eaton and once you reach it, it's time to start thinking about a blower upgrade.

In terms of bolt-ons, the Kenne Bell twin-screw is tough to beat. Offering a considerable chunk of additional boost and power potential combined with the immediate boost response you've come to love, the twin-screw can easily push your Cobra into the 10s. The Vortech centrifugal supercharger will easily produce more peak power than the Eaton (by a solid 200 hp or more), but that explosive top end charge is going to come with a penalty in low speed torque.

Fans of the centrifugal will love the never ending power surge, but whether Cobra owners will be willing to give up all that glorious torque remains to be seen. The turbo system easily offered the best horsepower and torque values, but like the centrifugal, the cost was low-speed torque production. At least in the case of the turbos, the explosion will come at just 3,900 rpm and not past 5,500 rpm like the centrifugal. In the end, what works best is all up to the individual Cobra owner.