Eaton vs Autorotor (Max Boost...
Eaton vs Autorotor (Max Boost vs. Max Boost)
Testing on the Lightning took a number of days and several long nights. The result was a wealth of information. During the testing, we swapped blower and crank pulleys (provided by Johnny Lightning) and tested just about every conceivable pulley and boost combination for both blowers. The Eaton was run with a combination of two different supercharger pulleys and four different crank pulleys. After cranking up the boost to the max with the smallest blower pulley (2.75 inches) and the largest crank pulley (9.00 inches), we decided to further improve the power output of the motor equipped with the Eaton supercharger. We installed a prototype single-blade throttle body from Accufab and a cone filter on the 90mm MAF to eliminate some of the inlet restriction. So equipped, the Eaton blower could only muster 15 psi of boost and produced 415 horsepower at the wheels. There was actually very little power gain by installing the smaller 2.75-inch blower pulley in place of the 3.00-inch pulley. All signs indicated that the Eaton M112 blower was about done at this power level. Installing the Autorotor with an identical set up (both pulleys and air inlet) resulted in a dramatic increase in power. With the same pulley ratios (2.75x9.0), the peak power jumped to 511 hp. Imagine that--over 500 hp at the wheels, and not just at some peak number. Equipped with the Autorotor, the Lightning motor exceeded 500 wheel horsepower for a full 1200 rpm.
After we installed the 9-inch crank pulley, the boost increased to 13.4 psi and the peak power jumped to 396 horsepower. Increasing boost pressure by just over 4 psi resulted in a gain of roughly 50 horsepower over the baseline runs. We tried a smaller 2.75-inch supercharger pulley on the Eaton, but the results were a less than dramatic 2-hp gain.
One thing we noticed during the runs was a sizable amount of vacuum present in the inlet system. The vacuum was a good indication that the inlet represented a flow restriction to the supercharged motor. To reduce the restriction, we installed a prototype throttle body and cone filter on the 90mm MAF in place of the factory air box. The changes resulted in an increase in power from 398 hp to 415 hp at the wheels. The Lightning was now making 415 hp at 15 psi (we gained boost by reducing the inlet restriction) through the stock cats. Supercharged motors are so rewarding to work on.
Our dilemma was now twofold. We had reached the reasonable rpm limit of the Eaton supercharger along with the limit of our available drive pulleys. The snout used on the Eaton M112 would not allow a smaller drive pulley than the 2.75-inch pulley we currently employed. The crank pulley was maxxed out at 9 inches. This combination resulted in a maximum rotor speed of 17,672 rpm at an engine speed of 5400 rpm. This was a sizable increase over the 13,500 rpm of the stock set up and well above the maximum rpm recommended by Eaton or Ford. Besides, the motor showed very little gain in power when we switched down in blower pulley size from 3.0 inches to the 2.75 inches (both using the 9-inch crank pulley). The blower was done, the available pulleys were done and now we were done, at least with the Eaton.
During testing, our data logging indicated that the charge temperature exiting the supercharger was 278°. Though the temperature exiting the blower was some 208° hotter than the 70° ambient temperature during testing, the intercooler reduced the 278° outlet temp to just 101° going into the motor. The air-to-water intercooler reduced the charge temperature by 167° at 15 psi of boost. Believe me, your motor would much rather breathe 101° air than 278°.
Next up was the Kenne Bell upgrade kit featuring the Autorotor MX420. A brief word on sizing is necessary here. The M112 designation from Eaton refers to the displacement in cubic inches. A displacement of 112 cubic inches is equal to roughly 1.84 liters. The MX420 Autorotor displaced 2.0 liters or slightly more than the M112. Though slightly larger in displacement, the Autorotor was actually at a disadvantage due to the use of the factory Lightning inlet.
In order to use the factory inlet manifold (attaching the throttle body to the inlet of the blower), it was necessary to top-feed the Autorotor in the same manner as the Eaton (see photos). Unfortunately, the twin-screw was designed to be fed from the rear. The requirement of top feeding reduced the efficiency of the twin-screw design by as much as 10 percent according to tests run by Autorotor.
Boost Curves with 3-inch Blower...
Boost Curves with 3-inch Blower Pulley
If there is one thing you can say about the gang at Kenne Bell, they are thorough. This graph is an example of that attention to detail. Every possible parameter was data logged during the testing on the Lightning. Here is a comparison between boost curves generated by the Eaton (lower) and the Autorotor (upper). The test was run with the same stock crank and 3-inch blower pulleys. Note the difference in boost curves generated by the two superchargers. The curves are similar, but the Autorotor offered more overall boost pressure through the entire run. Not surprisingly, the motor produced more power with the Autorotor, even though the pulley ratios were identical. The results of the power runs can be seen in graph.
The two-lobe Roots style does not suffer from the same problem with top feeding. If the results of the test are to be believed (the Autorotor people are very serious about their testing), a reduction of 10 percent brings the 2.0 liter Autorotor right on par with the M112 Eaton. Regardless of the small discrepancy in sizing, what we are really interested in here are things like charge temperature and power production.
After removing the Eaton M112, the gang at Kenne Bell had the Autorotor in place in no time. Installing the Autorotor on the factory Lightning lower intake required an aluminum adapter plate. The blower was further modified to accept the stock upper inlet casting to eliminate a new casting as the source of possible power gains. We wanted the power to come from the Autorotor blower and nowhere else.
The blower upgrade was equipped with the stock 3.0-inch blower pulley and stock (7.5-inch) crank pulley to match the baseline runs with the Eaton. The factory air box, 90mm MAF and throttle body were all installed to duplicate the runs made with the Eaton. No changes were made to any programming and care was taken to run the motor with the same beginning ambient and intercooler air and water temps. So equipped, the Autorotor pumped out a peak number of 403 horsepower.
This represented a gain of 55 horsepower over the baseline runs with the Eaton (using the same drive pulley ratio). That the Autorotor had more to offer than the Eaton was evident by the fact that the boost level was higher with identical blower and crank pulleys.
The boost pressure topped 13 psi with the blower upgrade. Imagine that--swap out your Eaton blower and gain 55 horsepower. Things were starting to look good here for our Lightning.
Equipped with the 2.75-inch...
Equipped with the 2.75-inch blower pulley and the 9-inch crank pulley, the Eaton managed 14.1 psi and 396 hp at the wheels.
Installing a prototype throttle...
Installing a prototype throttle body from Accufab and a cone filter on the 90mm MAF increased the peak power to 415 horsepower.
Our vacuum gauges indicated...
Our vacuum gauges indicated that the stock inlet manifold was a source of restriction at the 400-hp level.
With the Eaton maxxed out,...
With the Eaton maxxed out, it was time for the MX420 Autorotor supercharger from Kenne Bell. Note the modified entry on the Autorotor used to adapt the stock inlet manifold used on the Eaton. When tested on the 4.6 Saleen, the twin-screw design offered some serious power over the Eaton M90. Would the larger blowers react the same way?
Space limitations required...
Space limitations required use of the factory inlet manifold. Top-feeding the twin-screw design reduced the efficiency and therefore the effective size by as much as 10 percent according to testing performed by Autorotor.
Mounting the Autorotor to...
Mounting the Autorotor to the factory lower manifold required a custom aluminum adapter plate. Note the difference in discharge designs between the two blowers.
Simply bolting on the Autorotor...
Simply bolting on the Autorotor in place of the Eaton (with the same pulley sizes and air intake), resulted in a jump in power from 348 hp to 403 hp. The more efficient Autorotor increased the boost pressure from 9.3 psi to 13.2 psi at the same blower speed.
Unlike the Eaton, swapping...
Unlike the Eaton, swapping blower pulleys on the Autorotor was a snap. It took all of 45 seconds to change a pulley as compared to an hour or so for the Eaton. This means changing pulleys for 20-psi track use will be quick and easy.
We wanted to compare the two...
We wanted to compare the two blowers boost for boost, so we installed a larger blower pulley to slow down the Autorotor relative to the engine. Even with both blowers making a hair over 9 psi, the Autorotor out-powered the Eaton by 16 horsepower.