Those already sporting a built short-block can opt for the 2.8 blower. It's only $100 more than the 2.6 and puts out another 2 pounds of boost so it makes that extra horsepower you can't feel on the street but racers need. Physically the 2.6 and 2.8 blowers are identical, save that the 2.8 is 0.75 inches longer than the 2.6. All the rest is the same. The downside to the 2.8 is it makes two more pounds of boost than the 2.6, so instead of a lower limit of 10 pounds of boost like the 2.6, the 2.8 makes 12 pounds of boost, minimum. That's too much for pump gas and a stock short-block, according to Kenne Bell, hence the 2.6 option.
The other major part of the Two-Valve Mammoth blower kit is its namesake Mammoth inlet system. This is everything upstream of the supercharger, namely the air filter, mass air housing, inlet ducting and throttle body, all of which are truly huge in the Mammoth kit. That's because these items are on the naturally aspirated side of the blower, and pose tremendous restriction on airflow into the supercharger unless they are correctly sized, shaped, and placed in the engine compartment. It isn't as if the blower can power the air into itself; the stuff pushes in there the old fashioned way: the weight of the atmosphere drives it into the blower. If the blower inlet is restrictive then horsepower is lost and blower outlet temperatures rise, sometimes dramatically.
Kenne Bell has performed extensive flow-bench and dyno testing on blower inlets, and Jim Bell, the big rotor at KB, is evangelical about the need for low-restriction inlets breathing cooler air from outside the hot engine compartment. For the Two-Valve Mammoth application the solution was as easy as reaching for the Shelby GT500's Mammoth inlet. It's more than big enough for the Two-Valve 4.6.
Because the Mammoth Two-Valve kit is designed for a minimum of 15 pounds of boost, forged pistons, forged rods, and ported cylinder heads, Kenne Bell is offering it more as a tuner kit rather than a full kit. That means KB does not include any fuel system components, including fuel injectors, Boost-a-Pump, nor an electronic tune. Kenne Bell relies on the owners to upgrade those items, so there's no need to package them in a Mammoth kit. If the owner is stepping up from a stock or mild engine then they'll need to upgrade the fuel system and tune as the Mammoth Two-Valve kit can't be fed by a stock Two-Valve fuel system.
Setting a power figure to a tuner kit is an approximation, as the final number depends on injector size, the fuel system, boost, and tuning. However, out of the box (using the stock 5.0-inch crankshaft pulley, 2.750-inch blower pulley) for an entry-level 15 pounds of boost during an abbreviated 6,000 rpm test the Two-Valve Mammoth is good for 535 rwhp. That extrapolates to 580 rwhp at 6,500 rpm.
Set to pump 26 pounds of boost using a 6.50-inch crank pulley and 2.375-inch blower pulley the Two-Valve Mammoth put down an impressive 703 rwhp on Kenne Bell's Dynojet. There were no cats in the exhaust on that run. Set on kill, the Mammoth has put down an eye-watering 1,004 hp on an engine dyno (that's 218 hp/liter or 3.57 hp/ci, race fans) and 850 rwhp on heavily prepped Two-Valve race engines.
Real-world cost is also a moving target with a tuner kit. Kenne Bell offers the Two-Valve Mammoth kit starting at $6,199, but of course that doesn't include the necessary fuel system parts or tuning. Options are a polished supercharger (add $500) and an eight-rib pulley set (useful starting at just 15 pounds of boost; required at 20 pounds or more) for $699. You'll also need to choose among 5.0-, 6.5-. 7.5-, and 8.5-inch diameter crankshaft pulleys. There's more pricing information in the sidebar.
For once, we don't have to pass along a date for when the Two-Valve Mammoth kit will reach the market. It's been on sale since January 30, 2013, so you can have one right away. It seems like a powerful way to upgrade a hot-rodded Two-Valve Mustang, or as an alternative to an engine swap, or for a real surprise to unsuspecting Three- and Four-Valve drivers.
One concept that's apparent with comparing the standard and Mammoth Two-Valve kits is the importance of the inlet systems. We've touched on this idea before in this article and others, but it bears repeating: The inlet side of the supercharger is naturally aspirated and needs as careful attention to reduce restriction as any other naturally aspirated inlet system. Furthermore, the more boost and air volume the supercharger is processing the more important this phenomena is.
Kenne Bell has generous amounts of data showing the efficacy of large inlet systems breathing cool air on high-output supercharged engines; far more data, in fact, than we can show here. But to cut to the specifics of Mustang-based testing (on Coyote engines) KB's testing shows that in the 650 to 800hp range a 1 In Hg inlet restriction (about 0.5 psi) costs 32 hp, should you be engineering your own inlet.