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Supercharged 4.6L Two-Valve Motor - 2V Or Not 2V
Supercharging the 4.6L Two-Valve motor to keep up with the Joneses
The idea behind our first test was to install the Twin Screw blower with the standard 9-psi pulley system. Running 9 psi would show just how much power was available at the as-delivered boost level. Installing the Kenne Bell blower was straightforward. Initially, we installed 36-pound injectors, but were forced to replace these with 50-pounders from Holley once we started cranking up the boost. Next, we fabricated a direct drive for the blower from the crank pulley using a pair of idler/tensioners and a mounting plate supplied with the Kenne Bell kit. A used six-rib belt was sacrificed to measure the desired belt length. A trip to the local auto-parts store secured the proper belt and we were in business. The final chore was to run the intercooler (water) lines to and from the water source to air-to-water intercooler. Rather than run ice water, we relied on ambient temperature water from the dyno supply tank.
Westech’s Ernie Mena dialed in the fuel curve with the larger injectors. We decided on a conservative tune to maximize safety and ensure that the 4.6L was still in perfect running order after the blower test. The Kenne Bell was set up with the 75mm AccuFab throttle body to minimize inlet restrictions, but our system could surely benefit from the optional Kenne Bell Mammoth intake and single oval throttle body. The blower was equipped with a 278-inch drive pulley and run with the stock 6.5-inch (six-rib) damper.
The combination produced a blower speed of 14,243 rpm at a maximum engine speed of 6,300 rpm. The combination produced a peak boost pressure 9.3 psi at 3,700 rpm, but the boost dropped off slowly with engine speed down to a low of to 8.7 psi at 6,300 rpm.
Running 100-octane race fuel, the FAST XFI fuel injection was tuned to provide a safe 11.8:1 air/fuel raiot and 23 degrees of total timing. So equipped, the Kenne Bell blower upped the power numbers from 399 hp at 6,000 rpm to 602 hp at 6,300 rpm. The short-runner intake employed with the twin-screw blower allowed the motor to make peak power at a higher engine speed. The torque peak jumped significantly as well, from 390 lb-ft at 4,700 rpm to 538 lb-ft (produced plus/minus 2 lb-ft from 4,300 rpm to 5,400 rpm). That, my friends, is not only a ton of torque, but one flat torque curve.
While we were very happy that the modified ’97 motor was now making over 600 hp and (especially) 535 lb-ft of torque, like any good MM&FF enthusiast, we wanted more. Besides, we had yet to reach our goal of 700 hp! Knowing there was more left in the blower, we cranked up the boost by installing a smaller blower pulley. Stepping things up incrementally, we eventually doubled the boost pressure to just over 18 psi, where the supercharged Two-Valve produced peak numbers of 719 hp at 6,300 rpm and 697 lb-ft at 4,000 rpm.
The slightly falling boost curve was an indication that we either had an inlet restriction or that our 2.1L blower was getting near its maximum flow capacity. Having not logged the vacuum present between the throttle body and supercharger, we suspect both situations were present. If more power is desirable, then swapping over to the larger 2.6L blower and Mammoth intake might be a good idea, but just look at the power offered by this combination. If the question is 2V or not 2V, we’d say definitely 2Vwith boost!