We tried many ways to illustrate how huge a twin 75mm throttle body is, and this one seemed to work best. This immense billet monster is machined for Kenne Bell by a contractor to KB's specification, and it's essentially a mechnical version of the twin 75mm e-throttle KB uses on its GT 500 kit.
Since there was no way the stock twin 57mm throttle body could flow the required air volume, a giant Mammoth throttle body was developed. It's essentially a mechanical version of the throttle body Kenne Bell uses on its drive-by-wire S197 high-output kits and twin 75mm bores. For those of us who cut our teeth on "big" 70mm throttle bodies for 5.0 street cars 20 years ago, the twin 75 seems as though it's off a funny car or something.
Connecting the culvert-like 4.5-inch inlet tubing to the equally massive throttle body was done by pressing the stock rubber intake bellows off the Ford GT into Mustang duty. At its discharge end, the bellow clamps to the new aluminum intake, which bolts to the 2.8H supercharger.
Quantifying the new inlet system's airflow capabilities in cubic-feet-per-minute airflow shows just how impressive an improvement it is over the stock Cobra. Measured on KB's flow bench at 28 inches of water: Put another way, the Mammoth airflow path can flow nearly 2.5 times as much air as the stock Mustang Cobra intake. This illustrates both the huge power potential the Mammoth intake possesses (much more than 1,000 hp), as well as its low restriction on the naturally aspirated (suction) side of the supercharger.
While it may look as though the KB twin 75mm throttle body is closer to the camera than the stocker below it, they're both sitting on the same bench. KB uses a twin throttle plate because otherwise the throttle shaft bends when the throttle is snapped shut at high rpm. It takes a lot of air to bend a throttle shaft-and to make 700hp.
Bolting the supercharger onto the engine required a new mounting plate, because the slightly longer supercharger and much larger inlet casting required more firewall clearance. Ken used a two-piece mounting plate with Z-shaped registers for the job. This arrangement is considerably easier to install than the standard Terminator kit and is self-locating (registering), so it requires no more alignment than simply bolting on the lower plate, then sliding the top plate/supercharger assembly into position and installing the capscrews.
As for the name, during development of the immense intake, the word mammoth surprisingly came to mind and stuck. Thus was born the nickname and woolly mammoth caricature whittled into the identification plate recessed into the huge inlet.
System RequirementsChanges to the basic Cobra engine weren't needed to reach 704 rwhp, but at the elevated power levels for which this kit is optimized, a freer-flowing after-cat exhaust system proved necessary.
A quick glance under the prototype showed the cats and the first portion of the 3-inch Bassani after-cat system fitted during testing. The Bassani mufflers gainded 36 hp over the stockers at the mid 600hp level. Even better, it still amazes us a bolt-on Mustang can put 700hp to the tires.
The stock exhaust was run until the car reached 660 rwhp. At that point, the after-cat was unbolted and the test maximum of 704 rwhp was obtained. That's fine for track work, but obviously a good exhaust system is required on the street, so KB fitted a 3-inch Bassani aft-cat. Power was an amazing 696 rwhp, a mere 8hp drop from without mufflers or pipes.
Ignition breakdown is a typical problem at high boost, but KB achieved the 704-rwhp figure with nothing more than NGK TR6 sparkplugs gapped to 0.025 inch. This proved right at the limit for the stock ignition, however, and KB recommends its Boost-A-Spark box for 15-pound-or-higher boost applications. It won't show any more power on a dyno unless the engine is misfiring. It will clean up misfires at high boost and helps against the inevitable degradation in spark as the plugs and wires age. The BAS isn't included in the Mammoth kit, so it's an extra cost option at $229.
As for fuel, once again the excellent Cobra twin-pump fuel system proved up to the task, at least with a small current bump from KB's Boost-A-Pump, which is required and part of the Mammoth kit.
No other fuel system modifications are required up to 704 rwhp other than increased octane. Kenne Bell is aggressive on that, preferring to spend money on high-octane specialty fuels for track and dyno work to replace detonated engines. The company points out that 91-octane premium pump gas (the best pump fuel on the West Coast) is good to 565 rwhp with the Mammoth kit at 15 psi; East Coast tuners can squeeze another 30-35 hp with 94-octane pump premium fuel at 17 psi.