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Cylinder Heads

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

  All of the tumble port heads respond well to a port and polish job. Unless you have money to burn, justifying the additional expense of the FR500 heads may be difficult. The standard heads can be made to provide all the flow necessary for even the highest horsepower applications.
Twin port heads have never been offered for the 5.4L engines. You are limited to the Navigator heads unless you come across a set of Cobra R heads (you might have a better shot at hitting the lottery). Being limited to the Navigator heads is not a bad thing as these heads flow a large amount of air. Port and polish these heads and you will see port flow in excess 325 cfm. There is no horsepower to be gained by trying to run Cobra heads, the Navigator heads with their large ports allows the use of much larger intake runners. Below is an outline of the commonly available DOHC heads.
Twin Port Head
Dimensions (Intake)
Square Port 32mm x 40mm
Oval Port 36mm x 44mm
1999 & Later 4.6L Tumble Port (Intake)
50mm x 39mm
1998 & Later 5.4L Tumble Port (Intake)
59mm x 39mm

All DOHC Exhaust Ports
48mm x 25mm

Cooling System

The 4.6L, 5.4L & 6.8L cast iron blocks use a cooling system that is different from the one that is used on the aluminum blocks. The aluminum blocks use a bypass hose (this is the hose that runs in front of the engine to the thermostat housing) to keep flow constant through the block to help eliminate hot spots. This is due to aluminum being more susceptible to hot spots than is cast iron. If you are running an aluminum block do not eliminate this hose. The cast iron blocks utilize a conventional cooling system (no bypass hose).

  Oil System

The oil pump used on modular engines is what's referred to as a gerotor pump. It contains two internal gears with the middle one being driven by the crank. The clearance between the sides of the gears and the internal sides of the oil pump are critical. These pumps are not as robust as the pumps used on the older push rod Ford's. If any debris gets into the oil pump it will gall the sides of the aluminum housing, creating a situation where the pump will not prime. If you are reusing an oil pump be sure to pull the cover off the pump for a close inspection of the housing for galling. Replacing this pump after installation of the engine is not a fun job.
There have also been failures of the powdered metal gears utilized in these pumps when used in
hi-performance applications. There are billet pump gears being offered by some vendors to address this problem, do a search on Google and you will come up with several suppliers.
FRPP also offers a high volume oil pump. It is available under part # M-6600-D46 for 59.95. This pump is the same unit as is used in the Cobra's and does not have billet gears.

  Engine Weights and Dimensions  
4.6L SOHC 500 lbs.
5.4L SOHC 525 lbs
4.6L DOHC Aluminum Block 425 lbs
5.4L DOHC 540 lbs
6.8L SOHC V-10 640 lbs.
Accurate weights are hard to come by. It seems everyone has their own idea of what constitutes an engine assembly. Was it weighed with all the accessories, was it dry or filled with fluids, etc. Use this as a guide, these numbers are close but will vary from what you see elsewhere.
Dimension A measures from the top of the throttle body pad (if you are running our intake) or top of the factory intake (if stock) to the bottom of the factory oil pan.
Dimension B measures from the bell housing face to the front of the water pump pulley.
Dimension C measures from the outside edge of each cylinder head.
4.6L SOHC Mustang Intake
23 5/8"
5.4L SOHC F-Series Intake
28 "
23 5/8"
4.6L DOHC Cobra Intake
27 1/8"
23 5/8"
26 5/8"
4.6L DOHC Sullivan Intake
27 3/4"
23 5/8
26 5/8"
5.4L DOHC Navigator Intake
35 1/2"
23 5/8"
28 1/4"
5.4L DOHC Sullivan Intake
28 1/2"
23 5/8"
28 1/4"
6.8L SOHC V-10 Van Intake
28 1/2"
27 1/8"


Water Outlet / Oil Filter Mount

According to Babcox there have been at least 6 different castings for the water outlet / oil filter mount. These castings are interchangeable for all of the modular engines. The one you will probably want to use is found on the Cobras and some Mustangs. You can get it at your Ford dealer under part # F8ZZ6881AA. It retails for about 150.00. This casting accepts a factory oil cooler that also doubles as your water outlet, the water outlet exits above the power steering pump. The factory cooler is also available from Ford under part # F8ZZ6A642BA, it sells for about 150.00.
If you are running our 5.4L single plane intake and opted to relocate the alternator with our bracket, you will need the oil cooler housing off the 2003 cobra. The water outlet on this housing exits below the power steering pump. This cooler is available under part # 2R3Z6A642AA for about 150.00.



Engine Mounts

All of the modular engines have the same basic mounting locations on the cylinder block. This means you can take the mounts off a 4.6L Mustang Cobra, bolt them onto a 5.4L Navigator engine and bolt the engine directly onto the factory cross member. This scenario also applies to the 6.8L V-10, 5.4L SOHC, or the 4.6L SOHC.
The only exception to this is the Continental blocks previously discussed. For your information the Cobra R model used motor mounts that lowered the engine in the chassis 12mm, It did however, bolt onto the standard Mustang cross member. Something to think about if you are having hood clearance issues. If you are a
Mustang owner and want to go with a tubular cross member we very highly recommend Anthony Jones Engineering. Their cross members fit perfect and the quality is the best on the market. They can be reached




The 4.6L & 5.4L share the same exhaust port configuration. You can use a pair of Cobra shorty headers for your 5.4L DOHC transplant if you wish. None of the long tube headers currently available for the DOHC Cobra will work with the 5.4L swap inside a Mustang without modification. There are no commercially available swap headers at this time. Same thing goes for the 4.6L & 5.4L SOHC. There are several company's making shorty headers for the V-10, do a Google search for "Ford V-10 headers" and several will come up.


  If you have some good technical information for these pages, we would appreciate your sharing it with the rest of the modular community. Your contributions are what will help grow this database. You can e-mail your information (we will post with the information, who provided it) or questions regarding this database to: