Tom Wilson
December 14, 2009

The Engine
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.