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Two Valve Supercharger - Two-Valve Terror
How to keep up by making 700-plus horsepower with 281 inches, two valves per cylinder.
The question is a simple one--is the 4.6L Two-Valve still a player? As if Two-Valve owners don't have enough to worry about with the 300hp Three- and Four-Valve engines, Ford's new 5.0L Coyote upped the power ante by over 100 hp, pushing the Two-Valve even further down the performance totem pole. Now throw in the 400-plus-horsepower 6.2L and 6.4L engines from Chevy and Dodge, and you start to see the uphill battle faced by '96-'04 GT owners.
So, in a world of extra displacement, additional valves, and variable cam timing, can the original 4.6L Two-Valve still compete? The answer is yes, and while it would be difficult to build a naturally aspirated version to run with a new Camaro, Challenger, or Coyote, Two-Valve owners can go wild and wooly with boost.
Kenne Bell recently introduced a new Mammoth kit. The new system includes an oversized air filter, MAF, air intake tube, oval throttle body, Mammoth intake manifold, and your choice of a 2.6L or 2.8L supercharger. Even the lower intake that incorporated a dedicated air-to-water intercooler system was revised, meaning the blower and inlet system cannot be retrofitted to existing kits.
Given the fact that the 2.8L supercharger is capable of supporting over 1,000 hp on the right application, this new Mammoth system is capable of pushing power into the realm of the absurd. Kenne Bell has finally given Two-Valve owners the potential enjoyed by Four-Valve owners.
Big blowers are all well and good, but tremendous power comes from a combination of three things: the engine, the blower, and the induction system. Kenne Bell came through on its end, but a snafu on our end meant we didn't have quite enough engine to thoroughly test the new Mammoth system.
Our plan was to secure and/or assemble a suitable test engine capable of properly testing the merits of the new kit. Scheduling finally forced us to run what we had available, meaning a low-compression 4.6L short-block originally supplied by Sean Hyland Motorsports. The test mule was some six years old, had seen more than its fair share of abuse, and lacked a few components we desired for this test. First and foremost was the compression. We liked the fact that the short-block featured Scat rods and forged Wiseco pistons, but the dish design combined with the 44cc combustion chambers meant we were starting with a compression ratio below 9.0:1.
Our other concern was that the short-block was equipped with a cast (six-bolt) crank, which might become a problem on this high-boost application. Ideally we wanted a 5.0L stroker with a compression ratio over 10:1 to maximize naturally aspirated power before running the blower. In retrospect, wilder cam timing was also required--but enough whining. Let's bring on the boost!
We did have a great set of cylinder heads from Trick Flow Specialties. The Twisted Wedge Race 195 heads featured full porting and CNC chambers along with a 1.90/1.470 valve combination. These are by far the best heads available for the Two-Valve engine. The heads were teamed with a set of XE270AH cams from Comp Cams and run with both the stock PI intake and the Street Burner intake from Trick Flow Specialties prior to the installation of the new Kenne Bell Mammoth supercharger assembly.
After installation of the TFS heads and Comp cams, the naturally aspirated engine was run on the engine dyno using a Fast XFI/XIM management system, Kook's long-tube headers and a Meziere electric water pump. Equipped with the stock PI intake and Accufab throttle body, the low-compression 4.6L produced 348 hp and 349 lb-ft of torque. Stepping up to the TFS Street Burner intake and 75mm Accufab throttle body bumped output to 371 hp and 331 lb-ft of torque. The TFS intake offered as much as 45 hp at 6,500 rpm, but lost out to the long-runner PI intake below 5,300 rpm.
Satisfied with our baseline, it was time for boost. Off came the TFS intake and on went the dedicated lower manifold for the Kenne Bell Mammoth kit. Designed to accept a 2.6L or 2.8L supercharger, the intake offers exceptional flow and a dedicated air-to-water intercooler. The intercooler was important as we planned on running serious boost. Feeding the beast were billet fuel rails and Injector Dynamics 85-lb/hr injectors fed by an Aeromotive fuel system. We chose a 2.6L supercharger for this application, but the Mammoth system also features a revised intake manifold, massive single-blade throttle body, and 4.5-inch air-intake/MAF assembly. Airflow into the blower is critical, as inlet restrictions result in a drop in boost (and flow) out of the blower. Why restrict your 1,000hp supercharger with a 600hp inlet system? The Mammoth system was designed to maximize flow into and out of the Twin-Screw supercharger.
Installation of the Kenne Bell Mammoth blower required use of the front accessories. We installed the alternator (in its revised location), the A/C and power steering pump along with a Meziere electric water pump and idler pulley. Pulley swaps on the Kenne Bell were a snap, allowing us to start with a 4.25-inch pulley that provided over 10 psi, and finished the day with 22.6 psi using a 3.0-inch pulley. Belt slippage was eliminated with the use of the eight-rib upgrade from Kenne Bell. This required swapping out the stock six-rib pulleys on the alt, PS and A/C along with the installation of a 7.5-inch, eight-rib crank pulley. Running the 4.25-inch pulley increased the power output to 552 and 482 lb-ft of torque. The Mammoth offered a slightly rising boost curve, starting at 8 psi (at 3,000 rpm) and finishing at 10.7 psi at 6,700 rpm. In typical positive- displacement fashion, torque production was impressive, exceeding 450 lb-ft from 3,400 to 6,200 rpm.
After dialing in the supercharged combination, it was time to crank up the boost. We installed smaller and smaller pulleys on the 2.6L, stepping down in 0.25-inch increments. The 4.0-inch blower pulley brought 586 hp, while the 3.75-inch pulley stepped things up to 627 hp. Equipped with the 3.5-inch pulley, the 4.6L produced 670 hp at 17.5 psi. Stepping up to 20 psi with the 3.25-inch pulley brought 698 hp, but our final pulley swap to 3.0-inch pulley netted 742 hp. We tried a new radiused air entry designed by Kenne Bell on the oval throttle body that pushed the peak power output to 749 hp at 22.6 psi, but we stopped our testing there.
The blower will support considerably more power, but what we needed was more engine to start with. That would simultaneously increase power and decrease boost, making the blower even more efficient. Don't get us wrong, 750 hp is serious power from a supercharged Two-Valve, and we can't help but think there is even more power lurking in the Wooly Mammoth.