[GerRod]

Navigator heads and GT500 heads are NOT the same. What people fail to realize is that the GT500 engine is a "built" engine with ported and polished heads with high performance cams.... from the factory!

In 1999, Ford introduced the DOHC 4-valve 5.4 L in the Lincoln Navigator under the InTech moniker, making it the second engine to use this name. Ford later used versions of the DOHC 4-valve 5.4 L in the 2000 Ford Mustang SVT Cobra R, the Ford GT sports car, and the Ford Shelby GT500. The DOHC 4-valve 5.4 L is also used in the Ford Falcon line in Australia under the Boss moniker.
The SVT Cobra R version of the 5.4 L 4-valve V8 had several key differences from its Lincoln counterpart. While the iron block and forged steel crankshaft were sourced directly from the InTech 5.4 L, the Cobra R powerplant benefited from new, high-flow cylinder heads that were designed with features developed for Ford's "Rough Rider" off-road racing program, application specific camshafts with higher lift and more duration than other Modular cams, forged I-beam connecting rods sourced from Carillo, forged pistons that provided a 9.6:1 compression ratio, and a unique high-flow "cross-ram" style aluminum intake manifold. The Cobra R was rated at 385 hp (287 kW) and 385 lb·ft (522 N·m) though chassis dynamometer results have shown these ratings to be conservative with unmodified Cobra Rs often producing nearly 380 hp (280 kW) at the rear wheels.
The Ford GT version of the 5.4 L is a highly-specialized version of the Modular engine. It is an all-aluminum, dry-sump 5.4 L 4-valve DOHC with a Lysholm screw-type supercharger and showcases numerous technological features, such as dual fuel injectors per cylinder and oil squirters for the piston skirts, not found in other Ford Modular engines. The GT 5.4 L benefits from an improved version of the high-flow 2000 Cobra R cylinder head and unique high-lift camshafts. The GT is rated at 550 hp (410 kW) and 500 ft·lbf (678 N·m), though independent tests conducted on chassis dynamometers have shown these numbers to be conservative, with as delivered Ford GTs often producing nearly 550 hp (410 kW) at the rear wheels.


5.4 L 4-valve DOHC supercharged V8 installed in a 2007 Ford Shelby GT500
The Shelby GT500 uses an iron block 4-valve DOHC 5.4 L with an Eaton M122H Roots type supercharger and air-to-liquid intercooler.[10] The GT500 5.4 L shares its high-flow cylinder head castings with the Ford GT, with only minor machining differences, and shares camshafts with the 2003–2004 Ford Mustang SVT Cobra; which have less lift and duration than the Ford GT camshafts. All of the 5.4 L 4-valve engines destined for use in SVT vehicles, such as the Ford GT and Shelby GT500, have been hand-built by technicians at Ford's Romeo, Michigan plant.[6]