Kenne Bell Supercharger Install and Test - Ring My Bell

The first step was to install the Kenne Bell intercooled blower. We installed it along with the 61-pound Siemens Deka injectors (used in the car). The blower was set up with a 9.5-inch DUB crank pulley and a 4-inch blower pulley. Initial runs were made with the compressor bypass valve open to reduce the total boost pressure. Running a peak boost pressure of 9.2 psi, it produced 570 hp and 488 lb-ft of torque.

After dialing in the air/fuel and timing curves at the lower boost level, we closed the bypass valve and allowed every bit of the boost supplied by the blower to enter the motor. Running a peak boost pressure of 17.6 psi, the 4.6 produced 746 hp and 664 lb-ft of torque. Stepping down in blower pulley size from the 4.0-inch pulley to a smaller 3.75-inch pulley (using the same 9.5-inch crank pulley) resulted in a jump in boost pressure to 19.9 psi. The result of the pulley change was an increase in power from 746 hp to 767 hp. The peak torque was up from 664 lb-ft to 698.

Obviously, increasing the blower speed improved the power, but we knew there was a limit to the gains we could expect from more boost. You simply can't keep cranking up the boost. Looking elsewhere for additional power, we turned our attention to the intake and exhaust of the supercharged combination. First up was the intake. Since we were running without any MAF or attending air intake assembly, we looked at the throttle body and intake manifold between the throttle body and blower. Since the blower manifold was already equipped with an Accufab single-blade oval throttle body, Mihovetz decided to try a modified version of the blower manifold.

The revised intake featured cutting, welding, and porting, but obviously the power gains indicated the effort was worthwhile. The new intake upped the power output of the super-charged combination from 767 hp to an even 800 hp. As expected, the majority of the power gains were near the top of the rev range. This is indicated by a jump in peak torque of only 6 lb-ft (from 698 lb- ft to 704). Out near 6,500 rpm, the power gains offered by the revised intake exceeded 40 hp.

With the intake improved, we turned our attention to the exhaust. In the "Mods for Four-Valve Mods" series, we tested a set of 151/48-inch headers against a set of 131/44-inch headers on a Kenne Bell supercharged engine producing near 650 hp. At that power level, the smaller 151/48-inch headers offered the best overall power curve. With this combo exceeding that power level by some 150 hp, Mihovetz was sure the larger headers would be worth some additional power. As luck would have it, he had a set of headers from his old supercharged race car. The headers featured 171/48- to 211/48-inch step primaries and large 4-inch collectors. These race headers represented a significant step up from the 151/48-inch headers (with 2.5-inch collectors) we had been running previously.

The headers offered a significant step up in power, bringing the peak power numbers to 852 hp and 740 lb-ft of torque. Obviously, the 151/48-inch street headers represented a restriction on this high-horsepower supercharged combination. Before all you Cobra owners rush out to buy huge headers for your street cars, know that these headers will probably not fit in the chassis, and that most street applications (at least below 650 hp) will run better with the smaller primary tubes.

With the beginning and end of the airflow taken care of, we took a look at the middle portion, namely the intercooler. Suspecting the factory intercooler core was a restriction, Mihovetz modified the intermediate plate to change the angle of the air entering the core. He also modified the system to allow the use of the larger air-to-water core from the supercharged 5.4 Ford GT.

The drop in pulley size from the 3.75-inch used in all the previous testing to a 3.39-inch pulley combined with the intercooler upgrades resulted in an extra 50 hp, from 852 hp to 902 hp at 6,800 rpm. Torque production now exceeded 800 lb-ft, with a peak of 813 lb-ft at 5,000 rpm.

The final step was to replace the ambient dyno water run through the intercooler core with ice water (something that should be employed at the dragstrip at this elevated boost level). With discharge temps coming out of the blower exceeding 335 degrees (before the intercooler), the ice water offered a much-needed drop in inlet temps. The ice water proved to be a worthwhile modification, as the peak power jumped to 920 hp and 841 lb-ft of torque. Interestingly enough, use of the ice water dropped the boost pressure nearly 2 psi (from 24 psi to 22 psi). Given that this engine originally produced 720 wheel horsepower at 28 psi and was now producing 920 flywheel horsepower at just 22 psi, we'd say the exercise was a success.