The McKeowns have been a dedicated racing family for many years, most notably in the NMRA and NMCA ranks, but even as far as building NHRA Pro Stock truck engines before the class was relegated to the Sportsman level. Mark was unsure whether a tried-and-true Holley 4150 was the right choice for his engine, or if the high-tech FAST XFI fuel-injection system would make the most average horsepower through a broad rpm range. With a tremendous amount of dyno tuning experience in carb and EFI situations, the quality of the tuner would be a given, and the information would be reliable.
The engine that MME used as their testbed was one of the millions of two-valve 4.6L Ford engines that was produced for Mustangs, Town Cars, trucks, and cop cars from 1991 through the present day. The exact specimen began its life powering a van through 200,000-plus miles of reliable service, and was thoroughly seasoned. Ford cast their blocks at two different plants and designated the skeletons as either a Romeo or Windsor casting. Different main bearings, timing gears, crank flange bolt pattern, valve covers, and cam cap designs individualize the engines, but both are equally capable in terms of durability in the 500-600hp range where most high-performance 4.6-liters draw the line from badass street/strip car to serious race engine. The McKeowns' block was bored, torque-plate honed, and fitted to a set of matching Probe H-beam rods and forged pistons via Clevite rod and main bearings.
Taking advantage of Ford's R&D efforts, Mark used the factory crank blessed with undercut and rolled fillets that are proven to reduce stress risers and increase overall strength. Many high-performance 4.6L builds use a Cobra oil pump with its steel gears and high-volume design, but with the factory standard-volume pump producing over 80 psi of pressure throughout the dyno pulls, Mark felt justified not upgrading his pump. He does stress, however, that good oil pressure is critical on 4.6L builds to let the hydraulic cam followers (i.e. lifters) work correctly.