Richard Holdener
April 24, 2007

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Eaton Supercharged 4.6 (14 psi)
Roots blowers are great for producing a ton of low-speed and mid-range torque and the M112 Eaton was no exception. This 4.6 thumped out over 550 lb-ft from 3,000 to 5,200 rpm. The downfall of the Roots blower was that the peak power gains were not as impressive after upping the boost pressure from 11.7 to 14.2 psi. That the M112 was nearing its maximum flow limit was evident by the fact that the peak power was only up by 11 hp (583 vs. 572 hp) compared to the runs made at 11 psi.

Eaton Roots Vs. Kenne Bell Twin-Screw (14 psi)
The Kenne Bell twin-screw supercharger out powered the less-efficient Eaton Roots design, this time to the tune of 121 hp. Despite being spun more than 4,000 rpm slower than the Eaton, the twin-screw blower produced 704 hp at 14.5 psi. In terms of peak torque, the twin-screw produced 595 lb-ft and bested the Eaton from 3,500 to 6,600 rpm. Note how the power curve on the Kenne Bell continued to climb with engine speed.

Eaton Roots vs. Vortech Centrifugal (14 psi)
We suspect that minor belt slippage hindered the Vortech from producing maximum peak power, but the 725 hp number at 14.0 psi was still nothing to sneeze at. From 5,300 to 6,600 rpm the Vortech easily showed heels to the Eaton, but things were a different story below that point. As with any centrifugal supercharger, the boost (and power) curve increased with engine speed. Offering slightly less than 2 psi at 2,500 rpm compared to 12.3 psi for the Eaton; is it any wonder the centrifugal was down over 200 lb-ft? Were we to rev this motor to 7,000 rpm or beyond, the power gains offered by the centrifugal would be even more impressive. In the end, you have to decide if a storming top end is worth the trade off in low-speed torque.

Eaton vs. HP Performance Twin Turbo (14 psi)
Given the fact that the major gains offered by increasing the boost pressure on the Eaton were realized at lower engine speeds and that increasing the boost pressure on the turbo system had no effect until the turbos were at full song, the power difference at 2,500 rpm actually increased when we upped the boost pressure from 11 to 14 psi. At 2,500 rpm, the Eaton realized a torque advantage of nearly 180 lb-ft and carried a torque advantage until 3,900 rpm. If you don't have last month's issue handy, know that the crossover point for the Eaton and HP turbo system occurred at just 3,600 rpm at 11 psi. As before, once the turbos came up, they pulled away from the Eaton with a vengeance. Running 13.6 psi, the turbocharged Cobra motor produced 830 hp and 756 lb-ft of torque. Despite a slight boost deficit, the turbos out-powered even the most powerful supercharger by more than 100 hp. The turbos produced an extra 150 lb-ft of torque despite being down by almost one full pound of boost to the blowers.