need to know the cylinder head chamber volume, deck and compression height now to be sure its the same, or similar
DOHC C Head
98-up Lincoln Navigator
These 5.4L DOHC heads feature essentially the same intake port design as C heads, but they have a much larger intake port volume than 4.6 castings. Despite the fact that these heads feature a relatively small exhaust port, the extra intake port volume could be beneficial in helping fill a motor of greater displacement-think 5.4 liters. Expect slightly better midrange torque than even C heads, and sub-8,000-rpm horsepower production, although the larger intake port size leaves a slim selection of intakes to choose from when utilized on a 4.6 block. Forced induction fans take note-Navigator exhaust ports feature a thicker exhaust divider (while keeping the same overall exhaust port size as B, C, and FR500 heads) that allows coolant to circulate through this vital area. Conversely, the larger divider can also hurt flow by utilizing additional space in the port.
The real downside to Navigator heads, when used on a 4.6-based engine, is the severe limitation they impose on intake selection. The physically larger 5.4 heads don't leave a lot of room (when installed on a 4.6 block) between them for an intake plenum to sit-though they do bolt right up. Remember that since Navigator intake ports are essentially clones of those of C heads (just on a larger scale), they too suffer from the same intake port flaws that plague the earlier tumble-port design-no short-turn or floor in the throat of the intake port.
The extra port volume the Navi heads possess could be beneficial in filling a motor with greater than 281 ci of displacement, or in high-rpm naturally aspirated or supercharged street/ strip combinations. Fans of boost should remember the cooled exhaust port divider. Lack of intake availability is the real downfall of this otherwise wonderful casting.
Stock Intake Choices: None (4.6), '98-up Navigator (5.4)
Aftermarket/Modified Stock
Intake Choices: Al Papitto short-runner '99 Cobra (4.6), sheetmetal
Navigator Head Dimensions: Combustion chamber: 53 cc; Intake port vol: 184 cc; Intake port entrance: 2.290x1.400 in; Valves: 37 mm int, 30 mm exh