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PI head install for the 94-97 Ford 4.6L MN12's

One of the most rewarding engine performance upgrades has always been the Head/intake manifold upgrade. Allowing the engine breathe better will give you solid gains in both HP, torque and increased throttle response. The 1999 Power improved (PI - Performance Improved) 4.6/5.4 SOHC cyl. heads combined with the 1999 Mustang PI intake is a true testament in Ford’s ongoing quest on giving the masses what they want... Power baby!

Note that these are stock Ford heads, SVO or FRRP heads are aftermarket and flow slightly better but are more costly and do not come with cams and internals. The PI heads come complete except for the 2 1/8 oil plugs you need to install on the rear of each head. You can tell by the larger square intake ports that the air will flow like the wind as compared to the stock oval ports. A 3-angle valve job along with a little porting and polishing from a quality head shop will free up some extra HP but bring the cost factor up. The stock PI cams are aggressive enough for most applications.

The install for the newer 96-97 MN12's is easy but for the 94-95's it is a little more involved. The older cars will have to be customized a little to accept the newer style upper intake setup. The tools needed for the job are mainly the basics but some specialty tools are needed. Air is nice for the crank bolt and makes removing/installing the front cover bolts effortless. I have also made a list of optional side "while your in there" jobs that save in future headaches down the road.

If you want to install a blower in the future now is a good time to get the block ready for the task at hand. Installing the PI heads on a stock block will raise the Compression ratio because the chambers are tighter. The increased CR will have to be brought down some to compensate for forced induction. Installing a Mustang FRRP high volume oil pump involves removing the block and custom fitting an oil pickup tube for the MN12 pan. Reith Motorsports in Fla. can supply you with a custom tube for the MN12 pan.

The MN12 cars use two coolant senders one for the EEC and the other for the temp gage on the dash. The PI intake manifold will only accept one sender and using a TEE for both will give false readings and this causes a problem. I would think the most important sender would be the EEC sender so use the manifold fitting for that sender. The dash sender (smaller one) should be relocated inline with the heater hose coming from the water pump (as per Jerry). I have not done this mostly because I have the Cobra short and used one of the two holes in the side of the block.


1. Invest in a good service manual to aid as a reference. The HELMS Ford Service manual is by far the best if you are planning to service your MN12 yourself. I will focus on the "weird things" on the upgrade and try to give detailed instructions on the important 1999 aspects of the install.

2. I would buy the heads as soon as possible for they are like gold and are getting more expensive every day.

3. Never lay the heads valve side down this can damage the stems and seals. I would suggest look for a deal on a used 1999 Mustang engine especially for the 94-95 platform. Decide if you want to send the heads out to get massaged by a pro head shop (I used HBR in Fla.) or give it a try yourself. Head porting is not hard but you have to be very careful on the PI exhaust ports not to take off too much. Get a gameplan started on what extra mods your going to do on paper and go from there. The cardinal rule with any "upgrade" is it always turns out twice as much $$ as you first planned.

4. Clean the engine compartment real good and be sure to get the underside crud off. You want to be like a doctor going in to the operating room and try to be as clean as possible; dirt is not so good for engine internals.

5. The Increased airflow the PI setup ads will need to go out as fast as it went in so the stock exhaust manifolds need to be extrude honed or upgraded to headers.

6. You should install a higher volume fuel pump to match the added airflow. Follow the TCCoA tech page for the fuel pump install.

7. If you are considering upgrading the front sway bar take full advantage of the added room when the heads are off.

8. Replacing the timing chains should be not be questioned and they are cheap ($30ea). Be sure to inspect the timing chain components and replace worn tensioners and chain guides along with the chains if needed. Be sure to mark and # all electrical connectors especially the injector connectors and spark plug wires. MSD makes a nice plug wire number set that attache on each wire and they look pretty cool too.


1. Follow the teardown instructions in the Service manual for the heads and related components.

2. Remove the plastic cowl, wipers and hood if you need more room to work.

3. Removing the hood is easy and makes the job much easier for us larger folks.

4. After removing the crankshaft pulley bolt be sure the washer came off with the bolt before using the balance pulley removal tool.

5. The first problem child will be the power steering pump just relax and get to know a small 10mm open wrench a little at a time. The high-pressure power steering hose connects near the inside bolt and there seems to be no way in hell but take a deep breath and deal with it. You will be able to turn the bolt a little then adjust the wrench and so on.

6. The next beast is the head bolt you will have to use strong rubber bands to hold some of the outer head bolts up a little. The engine compartment will not allow you to remove these bolts so lifting them and holding them out of the block with rubber bands will do the trick. Also use the rubber bands to aid in the install of the new heads so remember the bolts needed help.

7. On the driver’s side head the dipstick tube is routed through the exhaust manifold and will make it difficult to remove the head. Have a buddy help you lift the driver side head with the tube attached. You need the newer Winsor dipstick tube so don't worry about damage to the old one.
The transmission dipstick tube is attached to the pass. side head don't forget that bolt.

8. Clean all gasket surfaces with gasket remover and cover the oil pan opening with a clean towel or something to block foreign particles from falling into the pan. Inspect the pistons and clean the carbon off the tops and also check the walls for problems. Do all the side stuff now while the heads are off you'll enjoy having the room to work.


1. Double check all surfaces on the heads for scratches and gouges UPS are know to mess up heads when in shipping.

2. Be sure all surfaces are clean and dry before installing the heads.

3. Install the 1/8 inch oil plugs before installing the heads. Ford saved money by using the same cast for the LT and RT heads they just install the cams differently for the respective head. That’s why you will need to install the oil plugs they seal the unused oil pressure holes needed to keep the chains tight.

4. The new timing chains should have come with 2 "bright links" on each chain. The links are use to line up the crankshaft marks and the camshaft marks. Start with the driver’s side head and Bring the #1 piston 10 deg BTDC (crankshaft keyway @ 9:00). Do this before lowering the head down to make sure the valves have enough clearance.

5. Install the Exhaust manifolds before installing the heads on the motor and align the cam marks close to were they should be.

6. The dipstick tube has to be installed in conjunction with the lowering the head and be sure to have the problem bolts banded up. Have a helper guide the tube from underneath the car while you hold the head just above the block. This is very hard and just try to take your time and try not to damage the tube and head surface.

7. Be careful not to move the head gasket while manhandling the head/tube.

8. Torque the head bolts as instructed in the manual and be sure to keep track of the torque sequence on paper to avoid costly mistakes.

9. Repeat install on the passenger side and install the chains following the manual exactly.

10. You will have to customize the water pump tube a little in order to fit the larger intake manifold. Take a little off the end of the tube and attach a small hose as a connector to the water pump tube in the valley. Use a 10mm bolt on the back of the driver side head to hold the tube in place.

11. The top 8 larger 1999 Mustang studs/bolts will be needed for the front cover. The front cover/head boltholes may (not necessairly) have to be drilled out a little to allow the thicker 10mm studs/bolts to go through use a drill press for this.

12. The valve cover install will be much easier with a 1/4 8mm-swivel socket along with a long 1/4 extension.

13. If installing on a 94-95 the 42-pin harness will have to be modified to compensate for the placement of the intake components. The TPS, IAC and EGR VAC sensor wires will have to be lengthened a little. Solder all connections and use shrink tubes over the connections.

Special tools needed:

* Crankshaft pulley removal tool
* Fuel line disconnect tools
* 1/4 8mm swivel socket for the PI valve cover bolts
* Cam holding tool (I used a large 3/4 Allen wrench in the end of the cams)
* Torque wrench
* Crankshaft holding tool (not really needed but nice to have)
* Large Rubber bands
* Teflon tape
* Gasket remover

..and while you in there (optional):

* Replace upper control arms
* Install Trans cooler
* Rebuild block with forged components (A must for forced induction)
* Motor mounts (they are prone to fail on the MN12)
* Sway bar
* Remote oil filter setup
* Trans rebuild /TC install
* Spark plugs and wires
* Fuel filter
* Oil pump
* Coolant hoses
* Extra heavy duty ground straps on each side of the motor (attached to the mounts)
* Upgraded belt tens.


These are TCCoA discounted prices, and are not for public consumption. With Dan Newman's approval, I am listing the realistic club prices, so our membership may properly budget this job. Please note that Ford updates their parts database monthly, and these prices will change. Note also; sometimes the physical part number changes. In the 2 months I have been working on this list, at least 7 part numbers have changed due to manufacturing improvements, etc. Those changes are reflected below. For up to the minute pricing, please call Dan Newman at Five Star Ford at: 800.866.1520 x 230.

Section One: Parts Needed for 1996-1997 Model Year T-Bird/Cougar

Part # Description/QTY Retail T.C.C.o.A. Cost Ea
XL3Z-6049-HA CYL HEAD (WINDSOR) $531.62 $360.00
XL3Z-6049-GA CYL HEAD (WINDSOR) $526.28 $360.00
1L2Z-9424-DA INTAKE MANIFOLD $250.05 $187.54
XL3Z-6582-BA VALVE COVER $71.73 $ 53.80
XL3Z-6582-CA VALVE COVER $80.02 $ 60.02
XL3Z-6306-BA SPROCKET $23.03 $ 17.27
YL3Z-9439-BA INTAKE GASKETS (2) $10.66 $ 8.00
XR3Z-6051-BA HEAD GASKET $26.57 $ 19.93
XR3Z-6051-CA HEAD GASKET $37.20 $ 27.90
F5AZ-6065-A HEAD BOLTS (20) $3.31 $ 2.48
F1VY-8255-A THERMOSTAT GASKET $3.34 $ 2.51
XW7Z-9448-BA EXHAUST GASKET(2) $19.38 $ 14.54
XW7Z-9448-AA EXHAUST GASKET $26.18 $ 19.64
N806300-S2 STUDS (8) $2.42 $ 1.82
F5AZ-6700-A CRANKSHAFT SEAL $7.30 $ 5.48
87836-S101 OIL PLUGS $1.90 $ 1.43
XR3Z-6754-BA DIPSTICK TUBE $6.82 $ 5.12
1R3Z-6750-BA DIPSTICK/INDICATOR $17.92 $ 13.44
D00Z-8597-B BYPASS HOSE $8.96 $ 6.72
C9PZ-18472-E 5/8" HEATER HOSE(2') $1.26/FT $.95/FT
F8ZZ-9276-AA FUEL PUMP GASKET $12.74 $ 9.56

Note: Re: the 3/4" to 5/8" heater hose reducer; Big Scott recommends getting a piece of hard tube at
Pep Boys, or any good auto parts store.

Section Two: Additional Parts Needed for 1994 -1995 Model Year T-Bird/Cougar

Part # Description/QTY Retail T.C.C.o.A. Cost Ea
F6ZZ-9F792-DA FUEL RAIL/MANIFOLD $169.98 $127.49
F6ZZ-9D475-CA EGR VALVE $74.04 $ 55.53
F6SZ-9D477-C EGR TUBE $49.77 $ 37.33
F8ZZ-9E498-BA VAC LINE HARNESS $28.82 $ 21.62
F6SZ-9728-A ACCELERATOR BRACKET $5.78 $ 4.34
F5PZ-9F715-AA IAC VALVE $63.70 $ 47.78
E83Z-9F670A IAC GASKET $.63 $ .47
F6ZZ-6C324-CA PCV VALVE & TUBE $14.00 $ 10.50
F6ZZ-8592-C T'STAT HOUSING $34.84 $ 26.13

The below items were not on the original list, but are recommended for a significant performance gain
for all model years covered by this mod

Part # Description/QTY Retail T.C.C.o.A. Cost Ea
XL3Z-12B579-AARM 80mm LIGHTNING MAF $151.71 $ 99.00
CORE CHARGE (80mm only)* $75.00 $ 75.00
1L3Z-12B579-AA 90mm LIGHTNING MAF $151.71 $ 99.00
F68Z-12A690-AA MAF WIRING (94-95) $18.95 $ 14.21
XR3Z-9B659-AA GT INTAKE TUBE $44.88 $ 33.66

*All 80mm LMAF assemblies are "remanufactured". They are no longer being manufactured as
"virgin" units. This is why there is a core charge on them. There are still some virgin
90mm units in inventory; hence, no core charge.

The 190 litre/hour fuel pump needed is available in various places. One example appears
on page 23 of the current Ford Racing Catalog, the other is available through
MN-12 Performance at This is a Holley piece, complete with
installation kit.

Part # Description/QTY Retail T.C.C.o.A. Cost Ea
FPK-100 (MN-12 PERF.) 190lph FUEL PUMP KIT $150.00 $150.00
M-9407-C50 (F.R.P.P.) 190lph FUEL PUMP $209.95 $176.67

All Ford Racing Products are available through Five Star Ford; with an approx. one week to 10 day lead time,
unless in stock in Scottsdale. Also; Walbro fuel system products are available through STEEDA Autosports, both
on line at or at 954-960-0774. F.Y.I: the flow rate of our stock fuel pump is approx.
88 litres per hour.

The below items are highly recommended for replacement while the engine is open. They are the timing chains,
and associated components.

Part # Description/QTY Retail T.C.C.o.A. Cost Ea
F3LY-6268-A TIMING CHAIN (2) $40.67 $ 30.50
F6AZ-6L266-CA TENSIONER $43.27 $ 32.45
F6AZ-6L266-DA TENSIONER $42.85 $ 32.14
F6AZ-6K297-AA GUIDE $14.00 $ 10.50
F6AZ-6K297-BA GUIDE $13.72 $ 10.29
1L2Z-6L253-AA ARM $10.25 $ 7.69
1L2Z-6L253-BA ARM $10.25 $ 7.69

The last item to be identified is the throttle body. You don't absolutely need to replace the T/B for
96/97, but it is recommended. For 94/95, it is mandatory. Air coming in through an 80mm or 90mm
MAF tube that hits a 60 or 65mm throttle body is restricted; as to defeat the purpose of the larger intake.
There are a number of after-market T/B assemblies out there. Check with Dan about a Ford Racing piece,
or go on line with Steeda. The books will tell you that the bigger T/B assy's are "not street legal". Well,
if we all followed those warnings to the letter, most of our cars would be in permanent dry dock. If you
don't want to replace the T/B (for 96/97; and in the case of adapting the new T/B in 94/95), consult your
local speed shop, or mechanic on how make the adaptation between the T/B and the new intake manifold.

Head Option: Ford recently moved all modular 4.6L engine manufacturing to their Romeo plant.
They have "homogenized" the production of the motors for both the Mustang GT and the Crown Victoria.
Reportedly, the Romeo heads have a higher compression ratio (9:4:1). However, it appears that the same
cams are being used for both vehicles. Dan and I checked the part numbers for the cams in both service
manuals, and they were the same. The Windsor heads for the 99GT will definitely have a more aggressive
cam. However, the Romeos use the same valve-covers as we have on our stock heads; saving a few bucks
vs. the Windsor. The Romeo Part Numbers are:

Part # Description/QTY Retail T.C.C.o.A. Cost Ea
1W7Z-6049-AARH CYL HEAD $500.00 $ 360.00
1W7Z-6049-AALH CYL HEAD $500.00 $ 360.00

Subtotal for complete list above (a couple line items are subject to your personal choice;
this is just for basic reference):

96/97 List: $2238.67 TCCoA: $1640.14
94/95 List: $2699.18 TCCoA: $1985.54

A couple final thoughts on options. A great performance benefit will be realized by porting
and polishing the heads. This will significantly increase airflow and horsepower. However,
it's another $600.00 - $1,000.00, depending on how specific you get with the job; ranging
from a mild street port, or a more aggressive job for racing, including polishing of the chambers.
The job begins to get a little pricey at this point. For some of the older cars, a better tack
might be to pick up a complete used 99GT motor. Big Scott reports that they can be had in the
$1,800.00 to $2,100.00 range. Check the classifieds, and the Recycler. If you decide to port &
polish; Sebastian & others recommend Fox Lake in Ohio to do the job. I chose JBA Racing in
San Diego. My decision was based on both reputation, and geography. Fox Lake is excellent;
but I didn't feel good about putting my new heads on a UPS or common carrier truck for a round
trip from California to the Midwest. Damage claims are a bear.

A number of other options arise as you get into the more esoteric reaches of the engine build.
I don't want to get into them in any detail here, because there are so many combinations possible.
It should be left to the tuning expert to configure; based on the many factors of the build up, including,
but not limited to: higher flow injectors, thermostat, electronic ignition, transmission options, rear-end
upgrades, nitrous, forced induction, and the like. The dollars really add up fast, and I don't want to
suggest that you need to do all these things. They are simply there if you want them.


Very special thanks to:

Big Scott, EECDOC, Paul99GT, Dan Geurts, Anthony J. Lewis, Dan Newman, Brian Ravitch
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