Muscle Mustangs & Fast Fords
Supercharged 4.6L Two-Valve Motor - 2V Or Not 2V
Supercharging the 4.6L Two-Valve motor to keep up with the Joneses
With the introduction of the new 5.0L, Four-Valve Coyote motor, the original Two-Valve has taken yet another step back in terms of popularity. The Three- and Four-Valve variants get all the publicity since they offer greater potential, but does that mean we should summarily dismiss the Two-Valve? Not hardly, as the Two-Valve remains popular due to its combination of availability and affordability.
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.
We followed this by building a dedicated 5.0L Two-Valve stroker using the only aftermarket heads in the industry. The 5.0L stroker combined additional displacement with wilder cams, elevated compression, and high-flow heads and intake from Trick Flow Specialties to create an impressive all-motor monster. So equipped, the 5.0L Two-Valve produced peak numbers of 463 hp and 430 lb-ft of torque. Adding a little shot of nitrous pushed the peak numbers to 604 hp and 588 lb-ft. Numbers like these bring serious respect on the street, as they thrust a Mustang into the 10s with sufficient traction.
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.
The ’97 4.6L Two-Valve (non-PI) motor was disassembled and sent out for machining and a new set of internals. We ditched the stock cast (six-bolt) crank, rods and pistons and installed a complete rotating assembly from Coast High Performance. On this application, we decided to stick with the stock displacement other than a 0.020-inch overbore. Coast High Performance supplied forged pistons from Probe Racing, each featuring a 10cc dish. When combined with the 45cc combustion chambers on the TEA-ported PI heads, the result was a static compression right near 10.0:1. Down slightly from either the previous PI/non-PI bolt-on motor or the 5.0L stroker, the 10.0:1 was a perfect compromise between the ultra low compression often run on forced-induction motors and the high-compression, all-motor combos.
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.
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.
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!
Power Numbers: Kenne Bell Supercharged 4.6L 2V
|N/A||9 psi||18 psi|
|NA||399 hp at 6,000 rpm, 386 lb-ft at 4,800 rpm|
|9 psi||602 hp at 6,300 rpm, 539 lb-ft at 4,400 rpm|
|18 psi||719 hp at 6,300 rpm, 697 lb-ft at 4,000 rpm|