The new kid on the block was...
The new kid on the block was the Vortech centrifugal supercharger. The T-trim offered impressive peak power potential.
A more detailed inspection of the various forms is in order, naturally starting with our baseline blower, the Eaton M112 supercharger (against which all others were eventually judged). This baseline status stems primarily from the fact that the Eaton Roots blower was chosen by Ford SVT as original equipment. As ecstatic as we are to have a force-fed Ford in the lineup (we can't say enough good things about this supercharged 4.6 Ford, so please continue with boosted Cobras in the future), the Roots blower simply cannot compete against the aftermarket blowers and turbos in terms of maximum power potential. If you've snuck ahead to check out the graphs, you'll realize that from a peak power standpoint, the Eaton was no match for any of the three.
What it did do was excel at producing low-speed boost (and torque) response. The centrifugal supercharger was easily outgunned at the lower speeds, but given free rein, the Vortech eventually caught and passed the Eaton. From an efficiency (hp per pound of boost) standpoint, the Roots blower will not measure up to any of the other three forms. What it does do is allow the motor to reach a predetermined power goal (and do so reliably) at the lowest possible price.
While the Eaton M112 may not be the prom queen, that's not going to stop this second-from-the-left cheerleader from spiking the punch bowl. True enough, the Kenne Bell twin-screw, Vortech centrifugal, and HP twin-turbo setup all promise (and usually deliver) hoards of performance, there are a great many Cobra owners out there who will never give up the factory blower. Whether on principle, economics, or factory loyalty, the supercharged Cobra came from Ford with an Eaton supercharger and by God, that's the way it is going to stay.
A custom fabricated (prototype)...
A custom fabricated (prototype) intake was used to adapt the stock throttle body and inlet to the factory lower manifold. This custom intake allowed use of the factory air-to-water intercooler core and lower intake.
I seem to have gotten off track a bit there with all the cheerleader talk, but the Roots blower does have plenty to offer. In addition to the low cost (relative to the others), the Eaton provides immediate boost and therefore power response. Stick your foot in the throttle of an '03-04 Cobra and you are rewarded with something sorely missing on previous quad-cam Cobras, that something called torque. The immediate boost response provides impressive low-speed and mid-range torque. Too bad under-hood space constraints limited the runner length of the intake manifold or we would have even more of the glorious stuff present, but the current (ultra short-runner) configuration is somewhat masked by the rapid boost response offered by the Roots blower. Only the positive displacement twin-screw can match the immediate boost response of the Roots blower. This, combined with the improved efficiency (lower inlet charge temps and more hp per pound of boost) and additional power potential, is why Ford saw fit to select the twin-screw design for the wickedly fast and powerful GT supercar. The Eaton M112 Roots blower was simply not efficient or powerful enough to meet the needs of the 550hp Ford GT 5.4.
Next on the force-feeder list is the twin-screw design offered by Kenne Bell. Manufactured by Autorotor, the twin-screw design takes the positive displacement supercharger to the next level in terms of efficiency and performance potential. The Kenne Bell twin-screw combines the immediate boost response of the Roots with a reduced charge temperature and increased flow potential. To put this added potential into proper perspective, we ran a test on the Kenne Bell blower last month in "Mods for Four-Valve Mods, Part 2." Removing the Eaton M112 and installing the Kenne Bell 2.2L blower with the same pulley size upped the peak power output by an amazing 145 hp! Where the Eaton supercharger checked out near 540 hp, the Kenne Bell went on to exceed 680 hp.
For the '03-04 Cobra, the Kenne Bell twin-screw blower upgrade makes an attractive package since it requires neither exhaust system mods like the turbo setup nor punching a hole in the oil pan (both turbos and Vortech). While the Kenne Bell can't quite match the efficiency of the turbos or centrifugal superchargers for maximum power, we've seen these blowers pump out over 700 hp at the wheels on an internally stock '03 SVT. That power potential pretty much takes care of the 95 percent of the Cobra market. Combine the immediate boost response (and attending massive torque curve) with the ease of installation and prodigious power potential, and you have what makes for a pretty impressive blower upgrade.
Eaton Roots vs. Vortech Centrifugal...
Eaton Roots vs. Vortech Centrifugal (11 psi)
Here is a perfect example of why I hate to see tests run where only peak power numbers are supplied. On the surface, that the Vortech supercharger produced 667 and 532 lb-ft of torque seems like a sizable gain over the 572 hp produced by the Eaton, but these numbers are somewhat misleading as indicated by the graph. The linear boost response of the centrifugal design meant that the boost pressure started at just 1.7 psi at 2,500 rpm. This compares to the 10 psi supplied by the Eaton at the same engine speed. Naturally 10 psi is going to produce more power than 1.7 psi, regardless of the difference in efficiencies. Down at 2,600 rpm, the Eaton topped the Vortech by 170 lb-ft. Had we provided just peak numbers and not complete graphs, you'd never know about the loss of low-speed power.
The new kid on the four-valve block came from Vortech in the form of its Cobra upgrade kit. Naturally, the highlight of it is a centrifugal supercharger, in this case, a very potent V-2 T-trim. According to Vortech literature, the T-trim is plenty powerful and is capable of supporting 825 hp. Like the Kenne Bell blower upgrade, the T-Trim Vortech system can feed the needs of the vast majority of Cobra owners, even those looking to go into the 9s. Again like the Kenne Bell blower upgrade, the Vortech system retained the factory Cobra air-to-water intercooler and front-mounted heat exchanger. We've seen (actually data logged) this very efficient core knock 200 degrees out of the charge temperature at elevated boost levels-so feel free to crank up the boost.
Unlike the Kenne Bell blower, which directly replaced the like-positioned Eaton, installation of the Vortech required fabrication of an upper intake. The upper intake was designed to replace the missing Eaton supercharger and provide a mounting position for the stock (or aftermarket) throttle body and inlet assembly. The fabricated intake was designed to receive the factory air-to-water intercooler from the Eaton and positioned the throttle body in the stock location. Boosted air is fed from the front-mounted blower into a cast-aluminum discharge tube, through the throttle body and fabricated intake, and finally across the intercooler core. Tubing is also supplied with the kit to attach the factory mass air meter, but none of our blower kits utilized this since we programmed each using the F.A.S.T. engine management system.
 Installation of the Vortech...  Installation of the Vortech required removal of the factory idler mounting bracket. Vortech supplied a custom mounting bracket to locate the supercharger just under the two radiator inlet necks. |  Vortech also supplied a few...  Vortech also supplied a few six-rib blower pulleys to allow us to dial in the boost pressure. Unlike the Eaton and Kenne Bell, the Vortech was driven off the six-rib system used for the majority of the other accessories. |  On the dyno, the Vortech produced...  On the dyno, the Vortech produced 667 hp and 533 lb-ft of torque. |