Installation of a 351W in an MN12

It is possible to install a multi-port fuel injected 351W into an MN12 car with a few slight modifications to the car and engine assembly. It is most easily accomplished on a 1991 - 1993 car equipped with the 5.0 Liter V8, but any Thunderbird or Cougar 1989 - 1997 is possible.

Major Parts Required

The most important issue when installing the 351W in an MN12 is the hood clearence. There will be plenty of room on the sides and in front of the engine, but the height is a difficult thing to overcome. Many of the parts listed here are the ones specifically needed to gain the neccessary hood clearence.

• Hood with a minimum of a 1.75 inch rise, so either of the popular hood designs for these cars (Mach I and cowl) will work
• Upper intake from a 1994 - 1995 Mustang Cobra; this meets up with the GT-40 style lower intake and is extra short
• V8 Accessory brackets for a 1991 - 1993 MN12 or a 1994 - 1995 Mustang
• 351W GT-40 lower intake, available from Ford Motorsport
• Large throttle body; use one made for a Thunderbird SuperCoupe
• Standard rear sump 351W oil pan; I would not recommend getting a new fancy one because it will need modified
• 190 lph in-tank fuel pump
• Minimum 24 lb/hr fuel injectors
• Motor mounts, all engine wiring, computer, exhaust manifolds, fuel rails, sensors, etc. from a 1991 - 1993 V8 MN12; I would suggest finding a wrecked one and buying the complete engine assembly if you are not starting with a 5.0 Liter car
• EFI Distrubutor for a 351W, used on the fuel injected F-Series trucks that had the 351W
• Larger radiator! A stock 5.0 MN12 radiator will not be enough for a 351W! Griffin makes high performance radiators for V8 MN12's - I recommend the HP Series for this particular setup. Ask for a radiator for a 1991 - 1993 Thunderbird 5.0 regardless of what car you actually have or they will want you to submit drawings and stuff. They don't seem to realize that they are all the same.

Other assorted pieces may be required, but these are the big ones. If your car does not already have the 8.8 rear, I would also suggest upgrading it unless you have some extra 7.5's around.

The Modifications

The engine is not just going to drop in the car in place of the 5.0 and have everything fit. Some things must be modified. First, make these modifications to the car:

• Cut a large chunk out of the fiberglass frame near the back of the hood. If you don't, the frame will land on the back of the upper intake. You should reenforce the frame with a piece of metal afterwards or it will not be strong enough. PICTURE HERE SOON
• Cut a small portion out of the plastic cowl panel - the one where the windshield wipers go into. Just trim a sliver off it or the upper intake will hit it in the rear. PICTURE HERE SOON
• In the center of the cross member, there is an oval shaped hole. You can see the power steering rack under it. There is a lip around the edge of the hole that should be ground off. It will make oil pan clearence much easier.

Parts of the engine assembly also will require modifications:

• You need to lose about 7/8 of an inch in the motor mounts. This is easily accomplished with the stock 5.0 MN12 mounts by opening them up, removing half the fluid container, cutting the height off the mount, and then welding it back together minus the half of the fluid container.
• To use the stock 5.0 exhaust manifolds (and unless someone can find headers to fit in this setup you will have to), they will need bent in order to clear the steering on the driver's side and the frame on the passenger side. They can be heated with a torch and either pressed or hammered to gain the proper shape. Both sides need to be bent in toward the engine.
• You will need to fabricate a new EGR tube to go from the passenger side manifold to reach the upper intake. The 351W is taller and the stock tube will not stretch. Use some copper pipe.
• The most important modification to be made is to the oil pan. The pan must be reshaped so that it does not hit the cross member when the engine is sitting on motor mounts that are almost 7/8 of an inch lower. Heat the pan with a torch and pound it with a hammer to reshape it. The most important areas will be right behind the small front sump and on the sides between the front and rear sumps. Get as much as you can without having the crank hit the pan, it is very important.

Installation

Install the engine very carefully and be prepared to remove it a few times after checking the height clearence. It is very tricky getting the engine to sit at a level where it is far enough away from both the cross member and the hood when you have such little total space to work with. A thin piece of cardboard should fit between the oil pan and the cross member, and you should have at the very least 1/8 of an inch between the upper intake and the hood (you should end up with more if you take the engine to its lowest possible point). I test the hood clearence by putting globs of Play-Doh on the upper intake and closing the hood. Putting a washer between the two parts of the motor mount can be used to increase the height if needed.

If you started with a 5.0 Liter MN12, you should just be able to plug in all the wires and go since the 5.0 HO and the 351W use the same firing order and the mass air computer will properly deal with the increased power and displacement. Those with 3.8 Liter cars will need to install a new computer and wiring. Use a computer and wiring harness from a 5.0 MN12 for the least amount of modification work. The engine wiring remained remarkably similar throughout all years of the MN12 up until 1994, so if you start with any 1989 - 1993 V6 you should only have to cut and splice a few wires together. I used a 1989 3.8 Liter Cougar and 1993 5.0 Liter electronics and only had to alter about five or six wires. Get detailed wiring diagrams for your car and the car you got the wiring harness from, and you should have no problems.

More questions? Email casey@amphibian.com

© 1999 Casey Leonard