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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
With our bottom-end ready, we reinstalled the ported PI heads from Total Engine Airflow. You will remember that the gang at TEA increased the flow rate from 177 cfm to 225 cfm, while the exhaust increased from 126 cfm to 208 cfm. Naturally there were gains registered throughout the lift range, from 0.050 lift through 0.600. The heads also received a valve-spring and retainer upgrade that allowed us to safely rev the motor to 7,000 rpm. The ported PI heads were combined with Comp XE274H cams, a stock PI intake and Accufab 75mm throttle body and elbow.
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.
We then turned our attention to forced induction. Knowing that boost is an effective replacement for displacement, we decided to set two distinct goals for our 2V or non-2V mod motor. The most obvious goal was to substantially increase the power output, but we needed to be realistic as well. This was not another one of those ludicrous 1,000hp build- ups, but rather a realistic evaluation of a boosted street combo. Having already reached the 600hp mark with our nitrous stroker, we decided that 700 hp had a nice ring to it. This was a realistic power number that would not tax the test motor. There was more power to be had from the combination at elevated boost levels, but 700 honest horsepower is enough to run 9s in the right chassis (quick by any measure of a street car).
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.
Looking to increases both horsepower and torque throughout the rev range, we selected a Kenne Bell supercharger. The positive displacement Twin Screw offered not only elevated efficiency levels to promote maximum power production, but immediate boost response. The immediate boost was responsible for the huge torque gains offered in the lower and middle rev ranges. Basically speaking, adding a twin-screw supercharger is akin to adding displacementthe result of which is more power everywhere.
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.