Cylinder Heads

4.6L DOHC
There are several different castings available for the DOHC heads. 4.6L & 5.4L heads will physically interchange, but the ports on the 5.4L heads are much bigger than the 4.6L heads. Neither the Cobra or Lincoln intake manifolds will work with this swap. If you were able to get the intake to bolt on, there still is not enough material around the ports to enable port matching to the larger navigator heads. Our single plane 4.6L intakes were designed with enough material to allow for this swap. The Navigator heads ports are too big for a naturally aspirated 4.6L street car but may make for some impressive horsepower on forced induction cars.

These heads can be divided into 2 basic designs pre-1999 twin port heads (also known as the "B" head) and post-1999 tumble port heads (also known as the "C" head). These 2 heads are interchangeable on any of the 4.6L blocks although it is usually not financially feasible to do this swap because it entails swapping intake manifolds as well. Both heads are very good castings with the tumble port heads getting the nod for making more high end horsepower. The heads on the Lincoln are the same castings as are used on the Cobra.

If you are building your DOHC engine for use in a truck or heavy car, you will probably be happier with the twin port heads. These heads with their IMRC plates, create better torque and at a lower RPM than the tumble port heads without severely limiting hi-end horsepower. These heads respond well to a port and polish job. You can also pick up extra horsepower if your engine is a Lincoln, by swapping the intake manifold for an early Mustang Cobra intake.

The tumble port heads have been available since 1999. These heads were never offered on the Lincoln Mark series due to the cancellation of this model in 1998. These heads can be found on the front wheel drive Lincoln Continental. Maybe if you come across a cheap Continental engine it's not such a bad deal after all. Obviously these heads are also available on the Mustang Cobra. The Cobra heads were modified for 2003. They are supposed to flow better on the intake and exhaust than the early castings.
The best heads offered to date have never been installed on a production vehicle. These are available on the FR500 crate engine. The heads on the FR500 are available from FRPP under part #'s M-6049-T46 and M-6050-T46. These heads are bare, but FRPP does sell a hi-lift (12mm) camshaft kit that includes cams, valves, springs, retainers, and rockers under part # M-6550-T46. The heads sell for about 800.00 each and the cam kit is 1495.00