For part two of our Boost...
For part two of our Boost Bash, we once again called upon the Ford Racing '03 Cobra motor.
In the movie world, sequels are rarely as good as the original. There are a few noted exceptions, like The Empire Strikes Back, Aliens, and T2. While the high-boost shootout between the four forms of forced induction can hardly be compared to the high-budget Terminator films, much like California's esteemed governor, in part one we did promise we'd be back.
As promised, here we are with the results of the high-boost testing performed on our 4.6 four-valve Cobra crate motor. For those of you who missed the last issue or skipped right over this juicy test, we'll do a brief refresher course. The idea behind the testing was to illustrate the differences in the boost and power curves offered by the four most popular forms of forced induction (Roots, twin-screw, centrifugal and turbos). To illustrate the differences, we ran all four forms on the same test motor (an '03 Cobra mill from the Ford Racing catalog) at the same boost levels.
In part one, we took the Kenne Bell twin-screw supercharger, the Vortech centrifugal supercharger and a twin-turbo kit from HP Performance and compared them all to the factory Eaton M112 Roots supercharger at 11 psi. Now here we are to perform the same test at 14 psi, and we even decided to toss in an intake runner length test along the way.
If you are interested in the theory behind the various forms, check out last month's issue. Basically, the positive displacement superchargers offer immediate boost response with the twin-screw bettering the Roots blower in terms of efficiency and power potential. The centrifugal supercharger offers even more power per pound of boost than the positive displacement superchargers, but lacks the response rate of either. In life, there is always a trade off and the turbo is no exception. Despite besting all the forms of supercharging in terms of peak power and torque, the turbo lagged behind the Roots and twin-screw blowers at the lower engine speeds.
As we indicated in part one of our "Boost Bash," we were not trying to declare a winner, but simply to illustrate the differences so the reader can make an informed decision. In most cases, the decision will not be based solely on the maximum (or peak) power potential. There are obviously other issues that come into play when choosing a supercharger upgrade or to simply retain the existing Roots unit. These variables might include cost, complexity, ease of installation and reliability, to name just a few.
 The baseline tests were run...  The baseline tests were run with the factory Eaton M112 supercharger. Though overshadowed by the other force feeders in this test, the M112 seems capable of producing 600 hp on the right combination. |  To ensure adequate air delivery,...  To ensure adequate air delivery, we installed an Accufab throttle body to feed the Eaton supercharger. |  Upping the boost from 11 (in...  Upping the boost from 11 (in the previous test) to 14 psi required nothing more than a pulley change. The DUB pulley systems from South Florida Pulley Headquarters made pulley swaps a snap. |
 Running a peak of 14.2 psi,...  Running a peak of 14.2 psi, the Eaton-supercharged 4.6 pumped out 583 hp and 574 lb-ft of torque. |  Next up was the Kenne Bell...  Next up was the Kenne Bell twin-screw supercharger. Many Cobra (and Lightning) owners have discovered the benefits of the twin-screw upgrade. |  Like the Eaton, the Kenne...  Like the Eaton, the Kenne bell blower was treated to an Accufab throttle body to maximize the airflow potential. Positive displacement superchargers are especially sensitive to inlet restrictions. |