The rectangular supercharger...
The rectangular supercharger exit is clearly seen from the bottom. The aluminum adapter plate is as thin as possible to maintain hood clearance, yet is strong enough to withstand the heat and load stresses of mounting the blower. The plate is notched in two places to precisely register the supercharger.
No changes were contemplated regarding the GT 500's complex, difficult-to-access harmonic damper and blower belt pulley arrangement. Being that it's a two-belt engine, changing the crank pulley for higher supercharger rpm isn't a practical option.
From the beginning, it was assumed the stock Ford intake manifold and charge cooling would be retained. KB's experience with the '03-'04 Terminator Mustang Cobra engines, as well as testing the GT 500, has shown Ford's charge cooling is the best there is. With the GT 500 mounting the blower atop the intake manifold-which flowed 1,700 cfm on Kenne Bell's flow bench-there wasn't a need for the expense or bother of a new intake-manifold casting.
Mounting the KB Twin Screw to the Ford intake manifold required the thinnest possible adapter plate, due to the tight hood clearance. Ken fabricated one from aluminum for the prototype. The photos show the tightly packaged bypass passages, mechanical-locking registration groove, and other adapter-plate details.
To follow up on the charge cooling, Ken says that he copied more than 12,000 numbers during the kit's development tests, and in that time, "I never saw the intercooler discharge temp go higher than 138 degrees. To an engine, that's freezing-cold air; anything less than 150 degrees is like candy to the engine. I made runs all day long and hot swapped a pulley [A two-minute job.-TW]; I'd run it and run it and run it. In August, it was 110 degrees and [the air-charge temperature] would stay 138 degrees or lower. It's amazing."
Wanting to leave the Ford...
Wanting to leave the Ford intake manifold unmodified, KB needed to build something of a maze for the bypassed air to find its way back to the stock inlet on the intake. The only way to do it was by routing the adapter plate and fitting a cover plate, as outlined by the flush screw heads.
Ken isn't kidding about the volume of data recorded during development. The dyno-run sheets number in the several hundreds and fill two large three-ring notebooks. The charge-air temperatures were taken from the OEM sensor, and the temperature probes Ken added so he could see the air temperature entering the mass air meter, exiting the supercharger, and inside the manifold downstream of the charge cooler. Boost loss across the charge cooler was also monitored. It never exceeded 1.7 pounds.
Kenne Bell also knew from the beginning they would focus on the inlet side of the supercharger. Because Twin Screw blowers ingest air at the firewall end of the supercharger, it has always been a trick to get the incoming air turned around from the air filter and mass air meter into the supercharger. Sometimes this has meant a slightly restrictive air-inlet casting because there wasn't enough room between the supercharger and firewall. On S197 Mustangs, this area is not so cramped. And given the sizeable, air-hungry Four-Valve V-8 and long 2.8 blower, the KB crew was determined to not starve the blower with the inlet-air casting.
With adequate room in front of the GT 500's firewall, the result is a huge blower inlet that easily flows 1,700 cfm, which is the intake manifold's maximum flow rate. Its oval opening is so large the GT 500's 2x60mm throttle body can't mate to its flange. A separate adapter plate had to be used to neck between the throttle body and inlet.
A suitably large bypass is...
A suitably large bypass is mounted at the right rear of the blower assembly. The tubing projects some, but the pieces can be easily accessed should any servicing be required.
Not surprisingly with computer modeling, the stock throttle body easily supports more than stock horsepower. Drawing on previous Ford GT experience where a 2x70mm throttle body is used, KB knew a larger throttle body would help but would also be expensive. The exotic GT uses a cable-actuated throttle body; the GT 500's is electronic, skunking what would have otherwise been the easy option. Furthermore, even a 2x70mm throttle body wouldn't be enough with the 700 rwhp the KB GT 500 was going to make at high boosts. Something larger was going to be needed, so Kenne Bell produced a prototype 2x75mm billet monster to table concerns about airflow.
The electronic throttle body took considerable tuning for Ken to make it work. The new version, available only through Kenne Bell, measures 2x77mm in final production. It's expensive, so the kits make do with the 2x60mm stock throttle body as long as possible; the 2x77mm unit isn't used until the final step. In fact, the big throttle body singularly takes the power from the low 700s to 800 rwhp.
Jim points out that people used to think a single 70mm throttle body was good for the 5.0 H.O. engine and a 75mm was too large. Now we need twin 77mm throttles.