5.0 Mustang & Super FordsHow To Engine
Kenne Bell Twin Screw Supercharger - Bell Curve - 3.6-Liter Twin Screw
Kenne Bell Raises Its Grade To 1,100 Horsepower With A 3.6-Liter Supercharger
John Mihovetz at Accufab gets credit for the beastly 5.4 under the 3.6 blower in this test. Commissioned by Mark Meiering to power his street/strip GT500 and assembled by Accufab tech Fred Grochulski, the engine starts with an exotic Ford GT aluminum block machined for wet-sump oiling and a standard starter, but from the head gaskets up its standard GT500 fare.
Internally it's all good stuff, of course. There's a stock eight-bolt crankshaft swinging forged, Manley rods and JE pistons with a healthy 10:1 compression ratio. Stainless steel rings are used.
The GT500 heads-the castings off Mark's Shelby-were CNC-ported. There's nothing trick in the porting department says the Accufab crew; just really small ports with places where the CNC didn't touch. These were hand-finished, so they are better than stock, but not radical. The valvetrain, except for John's trick (smaller than you think) camshafts, is all stock Ford.
Mark's stock intake manifold is used-that's what the Kenne Bell bolts to-with the supercharger kit taking over from there. One change for dyno duty is the throttle body is mechanical, with a throttle cable rather than the GT500's electronic unit. Fueling came from 95-lb/hr injectors on Evolution rails.
Headers have replaced the GT500 cast-iron manifolds. In the Shelby Mark runs 1 7/8-inch long-tubes, but on the dyno the engine was fitted with 2-inch primary beauties. They seemed to work great but won't fit in the car.
Two things intrigued us about the basic engine. The first was the stainless-steel piston rings. John likes them for durability in these hot-rodded blower applications, and notes they require a bit of brutality to break in. It takes immediate cylinder pressure to push the rings into the cylinder liners and get the hard rings to "cut-to-fit," and that cylinder pressure comes from WOT and blower boost. If you pussyfoot around during break-in, the hard rings will cut down the soft cylinder liners and never seat, giving you a lazy oiler of an engine. As a result, this engine went from freshly assembled to WOT on the dyno for break-in purposes.
Our other question was how in the world does John, who was doing all the electronic tuning with admittedly high-buck Motec software, get away with combining gasoline, 10:1 compression and 25 pounds of boost? "Everything has to be just perfect," was his quick response, noting the dyno session used expensive 116-octane C16 leaded race fuel, and that 16 pounds of boost was the limit with 93-octane pump gas.
By "perfect," John was referring to the electronic tune, which he carefully developed with extensive, expensive real-time monitoring and environmental tools (wideband oxygen sensors, dyno-controlled cooling water, and so on). More fundamentally, John has found the Four-Valve Ford's combustion chamber to be detonation resistant if a flat-top piston is used-he pushes the piston up in the cylinder with a relocated piston pin rather than putting a raised dome on it. "You could never do this with a Two-Valve," said John, because the Two-Valve lacks the Four-Valve's centrally located sparkplug and even airflow characteristics.
John also gave us a powerful clue to modular power production by noting he's found raising the compression ratio absolutely fundamental in his Four-Valve experience. He tested this theory by building otherwise identical engines for his own turbo'd 4.6 racer, one with 8.5 compression and the other with 12:1. The higher compression gained over 300 hp!
On the Dyno
This was a Kenne Bell test, but the crews from Westech and Accufab were there and hands-on as well. It was something of an all-pro event. Besides simply proving and tuning the engine for owner Mark Meiering, the session was designed to test the new 3.6-liter blower relative to the proven 2.8-liter Kenne Bell supercharger.