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Old 12-21-2004, 11:51 PM   #1
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FAQ Collection

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Old 12-22-2004, 12:07 AM   #2
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Re: FAQ Collection

Well I have found out there is not much information on the internet concerning 4v DOHC Modular Motors and their parts. There was a good informative thread, but it has been lost by another forum.

So I’ve decided to start a collection of this information to help anyone building a 4v motor. This is a work in progress so bear with me. If you would like to contribute, please do so I would appreciate it. If you see any mis-information please let me know.

Short Block

Aluminum Block with 8 bolt crank.
Weak rods and Pistons.
Block and crank good for 1000+ horsepower but don’t try it on stock rods.
10:1 Compression

Aluminum Block with 8 bolt crank.
Stronger rods but same pistons.
10:1 Compression

Iron Block with 8 bolt crank.
Manley Rods with Forged Pistons.
Good for 1000+ horsepower.
8:1 Compression


B-Heads (96-98 Cobra; 93-97 Lincoln Mark VIII; pre-99 Lincoln Continental)
Nicknamed the “swirl port castings.” They have twin intake ports, one primary and one secondary, with the infamous IMRC plates. Not good for a N/A head, best used in boosted applications.

C-Heads (99-01 Cobra; 99 Lincoln Continental)
Nicknamed the “tumble port heads.” These heads have a single intake port with a smaller cross section which boosts airflow velocity. Good for midrange torque and power production. Good N/A street head but power production is pretty much limited to 8k rpm.

FR500 Heads (FRPP Catalog)
Basically the same as the C-Head but with a larger intake port. Capable of power production beyond 8k rpm.

03’ Heads (Cobra; Marauder; Aviator; Mach 1)
Possibly the best flowing small displacement head. The heads have the same flow capacity as the intake side of the FR500 head, but with a larger rectangular exhaust port. The best all around head and the absolute best for boosted applications.
*Note*: There is an unconfirmed report of “blue stripe” heads now being produced to fix the ticking problem experienced by a number of 4v owners. They can be identified by a blue stripe painted on the back side of the head facing the firewall. It is rumored that they have better cooling passage layout compared to early 03 production castings.

Navigator Heads (99+)
Same intake port design as the C-head, but with more volume. It also has the same small exhaust port as the B/C heads. Requires a modified 99-02 or custom sheet metal intake.

Intakes - Cobra Only

Upper Cover / Lower Intake Design
Dual Butterfly Throttle Body
Runners split into two intake ports
One port (secondary) is covered by a butterfly valve which is opened at 3300rpm by the IMRC controller to allow more airflow.
IMRC = Intermediate Runner Control

Upper Cover / Lower Intake Design
Dual Butterfly Throttle Body
Shorter Runners than the 96-98
IMRC’s eliminated
Best all-around Intake

Roots Blower / Intercooler Design
Will only work with Eaton or Kenne Bell Roots blower setup



Chain Drive

Front Cover

Head (Cam) Covers

Interchangable between Production Heads. Only dependant factor is the ignition that you use, External Coil Pack covers will not work with Coil on Plug Covers.


Dependant on Chassis, Displacement, and Head Model. All headers are Ford Production Cast variations with all the flash and kinks possible. Suggestion: Go aftermarket.

Fuel Delivery

ECU and Harness


Modular 4v Cooling Mod

This mod consist of two stock Ford coolant necks that allow hot coolant to escape from the rear of the heads. Very popular with 4v Cobra owners who have had the dreaded "tick" or the 7&8 cylinders fail. A must have mod for ANY rebuild.

Parts Needed

18" of Standard Heater Hose (your stock size, varies with year)
Plastic Tee fitting (size of your heater hose)
3 Standard Screw Hose Clamps
Drivers Side Part #: ????
Pass. Side Part #: XR3Z 18B402-DA

I could only find the part number for the Passenger side. Help me out on the drivers, please.
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