Richard Holdener
December 1, 2004
Eaton vs. Kenne Bell vs. Vortech vs. HP Perf Boost Curves (11 psi)
To some extent, the power curves simply mirror the boost curves, but check out the differences in the boost curves offered by the four forms of forced induction. The positive-displacement blowers (Eaton and Kenne Bell) have similar boost curves, though notice how the boost curve supplied by the Kenne Bell rises after 5,000 rpm while the Eaton tapers off. The Vortech centrifugal blower produced a rising boost curve, producing peak boost pressure only at peak engine speed. The HP twin-turbo system offered only slightly more boost than the centrifugal at the lower engine speeds, but came on strong about 3,500 rpm. Real tech heads that compare the boost readings from this boost curve to the power readings on the power curves will realize that the turbo system started producing more power than the Roots blower well before the boost pressures became similar. The crossover point for the turbo and Eaton in terms of power was at 3,650 rpm. At this point, the Eaton was producing 11.5 psi while the turbo was only producing 8.5 psi. The turbo equaled the power output of the Roots at 3-psi less-boost-pressure. No wonder the turbos went on to make more power.

After a series of back-up runs, we removed the Eaton supercharger and swapped on the Kenne Bell Cobra upgrade kit. The upgrade kit included a 2.2L twin-screw supercharger designed to produce not only immediate boost response but also impressive ultimate power potential. Installing the Kenne Bell required removing the intercooler core from the bottom of Eaton supercharger. The 65-psi injectors were also swapped over and run in conjunction with an Aeromotive A1000 pump augmented with a Kenne Bell Boost-a-Pump to assure adequate fuel flow to our boosted combination. Kenne Bell also supplied a Boost-a-Spark to increase the supply voltage to our ignition. The Boost-a-Spark eliminated any misfires associated with insufficient ignition energy. The Kenne Bell was run with both a smaller crank (7.5 inches) and a larger (3.75 inch) blower pulley. The combination reduced the blower speed considerably (by roughly 2,000 rpm) compared to the Eaton, but that didn't stop the twin-screw from pumping out 629 hp and 525 lb-ft of torque at a maximum boost reading of 11.9 psi. This was as close as we could get to matching the peak boost pressures given the availability of pulley ratios.

After running the Kenne Bell, we installed the new Vortech blower upgrade. Like the twin-screw from Kenne Bell, the Vortech kit retained use of the factory air-to-water intercooler core used with the Eaton. It was necessary to fabricate an upper intake to facilitate use of both the factory intercooler and throttle body/inlet assembly. The fabricated Vortech intake positioned the throttle body in the stock location, as well as allowing use of the stock fuel rail. The downside to this fabricated upper intake is that it lacks any semblance of torque-enhancing runner length. Check out Part 2 for a test on the effectiveness of adding runner length, but for now know that the Vortech was being tested with the same intake used by the Eaton and Kenne Bell blowers. Equipped with the Vortech, the peak power numbers jumped to 667 hp and 532 lb-ft of torque. Judging by peak numbers alone, you'd think the Vortech was the way to go, but know that the added top-end power came with quite a cost. Given the linear boost curve supplied by the Vortech, the boost was off by as much as 8 psi and low-speed torque by 170 lb-ft compared to the Eaton. The beauty of the Vortech centrifugal supercharger is that you can easily crank up the boost pressure and power to levels not attainable by the Eaton, but at this relatively low (and equal) boost setting, all that extra torque produced by the Eaton looked tough to beat.

The twin-turbo system was run with a stock '01 Cobra intake manifold and twin-blade throttle body.

The final test involved the installation of the twin-turbo kit from HP Performance. Initially we were dreading the installation, thinking that the turbo kit must be much more difficult to install than either of the two superchargers. While this may be true to some extent in the car, on the engine dyno, hooking everything up was a breeze. We'd previously removed the pan to drill and weld a fitting for the oil drain-back used by the Vortech supercharger. Knowing we planned on testing the twin-turbo kit, we simply welded two fittings in place on the front of the oil pan. The Flowtech headers were replaced with the supplied (Jet-Hot-coated) tubular exhaust manifolds and hooked up to the pair of 57mm turbos, wastegates, and air-to-air intercooler. We relied on a fan and water mist to keep the core cool during our runs (the temps were monitored digitally). The inlet system on the HP kit from the intercooler to the stock throttle body was designed to be run with the mass air meter. Since we were running no MAF, we combined the Vortech inlet casting with the HP tubing to bypass the eliminated MAF. Using the Turbo XS manual boost controller, we upped the boost pressure until reaching our running pressure of 11 psi. Run at 11 psi, the turbo kit pumped out 750 hp and 679 lb-ft of torque, bettering all three of the superchargers.

Check out the supplied power and boost graphs for a complete rundown on how each system performed. As expected, the Eaton blower provided immediate boost response and despite the short-runner factory intake, produced impressive low-speed and mid-range torque numbers before falling off at higher engine speeds. The torque output of the supercharged four-valve motor exceeded 500 lb-ft from 3,100 rpm to 5,200 rpm. Spinning slower to keep the maximum boost pressure in check, the twin-screw lost out slightly at the lower engine speeds, but made up for the difference in blower speed with improved efficiency. Where the boost pressure fell off with the Eaton supercharger, the boost (and power) kept climbing with the Kenne Bell blower.

As expected, the Vortech out-powered the other superchargers at the top of the rev range, but lost out in terms of torque production big time compared to the positive-displacement blowers. Like the centrifugal supercharger, the turbos lost out at the lower engine speeds until the turbos came up on boost. Below 3,600 rpm, the Roots blower was the clear winner, but once the tach needle swung past 3,600 rpm, it was all turbo. How does an extra 178 hp and 154 lb-ft of torque sound? While the turbos were down by as much at 100 lb-ft at 2,500 rpm, they quickly made up for lost time by eclipsing the Eaton and producing the most impressive (post-4,000 rpm) power curves of the bunch. Check out the power and boost graphs and check back with us next issue when we crank up the test pressure on each system to 14 psi and bring you a test on the effect of runner length.