Supercharged 4.6L Two-Valve Motor - 2V Or Not 2V

Though not technically a series, we recently ran a pair of articles on the 4.6L Two-Valve motor in the last few issues. The first article dealt with adding bolt-ons to a wrecking-yard motor. Replacing the non-PI heads, cams, and induction with a pair of ported heads from Total Engine Airflow, a set of Comp cams, and the PI induction system increased output from 260 hp and 341 lb-ft of torque to 390 hp and 384 lb-ft. Obviously, the 4.6L GT motors respond well to bolt-ons, as we were able to improve the output by 130 hp by simply replacing the heads, cams and induction.

Happy as we were with the results of both the bolt-ons and all-motor/ nitrous combinations, we couldn’t help but notice that our Two-Valve had yet to be subjected to boost. Knowing every motor deserves positive pressure, we decided our next move would be forced induction.

Before moving to our boost builder, we had a decision to make. Having built a pair of Two-Valve motors already, we had to choose one to supercharge. In one corner was the wrecking-yard short-block equipped with ported heads, cams, and PI induction; in the other was the high-compression 5.0L stroker. Unfortunately, neither was ideal for boost, as the stock internals on the 4.6L (bolt-on) motor would not withstand our intended power levels. The 5.0L stroker was sporting forged internals, but the high static compression (over 11.0:1) made it less than ideal for anything but an all-out race-fuel effort.

In the end, we decided to upgrade the short-block on the wrecking-yard motor with forged internals. We wouldn’t be using the very desirable heads and induction system from Trick Flow Specialties, but we liked the idea of having the 5.0L stoker ready to run.

Running 10.0:1 instead of 9.0:1 or even 8.5:1 will make the motor much more responsive off boost, to say nothing of improving both fuel mileage and overall power. The forged pistons were combined with forged (stock length) connecting rods and an eight-bolt, forged-steel Cobra crankshaft. Naturally the eight-bolt crank required a matching flywheel or flexplate, but we had that at our disposal for dyno use. After installing the forged rotating assembly into the freshly machined block (by L&R Engines), our short-block was officially boost-ready.

For maximum sealing, the TEA-ported heads were installed using Fel Pro MLS head gaskets and ARP head studs. The new modular combination was treated to a proper break-in cycle using Lucas oil, then run in anger in normally aspirated trim before adding boost.

Run normally aspirated, it produced 399 hp at 6,000 rpm and 390 lb-ft of torque at 4,700 rpm. Torque production exceeded 350 lb-ft from 3,800 rpm to 6,000 rpm. These were impressive numbers for a normally aspirated 4.6L Two-Valve, especially one equipped with the stock PI intake manifold.

Goal number two was to not only improve the peak power substantially, but rectify a design deficiency of the modular motor family. The narrow bore spacing limits bore size, and ultimately displacement. The lack of displacement limits torque production, as torque is definitely a function of engine size. Obviously boost would help offset the lack of torque, but all boost builders are not created equal.

Given the street/strip nature of this buildup, we appreciated the fact that the Kenne Bell supercharger kit also featured a dedicated air-to-water intercooler (just like all the factory Ford Lightning, Terminator Cobra and GT500 systems). Because of their superior heat transfer (water is denser than air), air-to-water intercoolers can be made significantly smaller than typical air-to-air intercoolers. Both systems offer specific merits for street applications, but for maximum heat rejection, nothing compares to the air-to-water (especially with ice water). The heated debate aside, it is more important to the average enthusiasts that the supercharger system incorporates an intercooler than which system is actually employed. Cooler air is better for both power and as a ward against harmful detonation.

Kenne Bell offered both the 2.1L and 2.6L superchargers for the Two-Valve, and though it may surprise some, we opted for the smaller unit. The larger 2.6L was certainly capable of supporting more power, but the 2.1L was more than adequate for our self-imposed maximum power output. Besides, the smaller blower offered improved boost (and power) response at any given maximum boost level, until such point as the small blower ran out of flow rate.

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.

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.

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!

Power Numbers: Kenne Bell Supercharged 4.6L 2V

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