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1,013 Posts
Discussion Starter #1
Sick of the sluggish 3.8? Aren’t we all… Luckily one of the easiest engine swaps is not out of reach for the V6 MN-12 owners. The Split-Port 4.2L V6s found in ’97 and newer F-150 trucks offer 210 hp and 255 lb-ft of torque in stock trim. The 3.8L V6 pumps 145 hp and about 175(?) lb-ft at best (stock). This weakness combined with the constant reminder of the poor head-gasket design often makes V6 owners wish they had a V8. Although the V8s offer better performance, they do have reliability issues of their own (leaky valve seals; cracking intake manifolds). Although a swap to a 4.6L V8 or 302 would be a step up from the 3.8L, the cost involved would make it unreasonable since it would be easier to sell the V6 and buy another MN-12 with a V8. But what’s the fun in that, right?! Besides, the 4.2L bolts right up to the 4R70W (don’t know about AOD). So with no further ado….

When selecting the perfect 4.2L V6 for your car, look for a ’98 or newer. The ‘97s have two problems which can be fixed, but usually prompt people to look elsewhere.

Problem 1-
The bottom end of the ’97 4.2L is different from the rest. It does not clear the 2001 V6 Mustang oil pan and oil pick-up tube. The picture below shows the new pan on the ’97 4.2L assembly. The engine is upside down.

This can be resolved by acquiring the main bearing cap girdles off of a later 4.2L and swapping it with the over-sized girdle (seen below). Removing the girdle and not replacing it is a bad idea.

The ’97 girdle is actually two separate girdles underneath some sort of windage tray. One bracing bearing cap studs 1 (front-most pair) and 2, and the other bracing 3 and 4 (rear-most pair). The newer girdle holds cap stud pairs 2, 3, and 4 while the #1 pair stands alone. The front cap studs need to be cut-down on the ’97 to clear the Mustang pan. I used a rotozip with a grinder attachment.

The work to adapt the ’97 lower end is not that hard. What is hard is finding the new girdle to fit the application. The girdle is NOT available from Ford unless you buy the entire block assemble with it. By purchasing the ’97, you are hoping someone has ruined a ‘98+ 4.2L and is willing to sell you the girdle on its own. Another girdle could probably be fabricated, but the cost would not make it worth it.

Problem 2-

I do not have experience with this particular problem (yet) but I want to make sure people know about it. The ’97 truck engines apparently had a problem during assembly. The timing cover bolts were not tightened enough. Around 40k miles, these engines have been known to leak coolant into the engine, causing it to mix with the oil. If not caught, this could cause a spun bearing or worse. This always means a costly rebuild. The solution is to purchase a new timing cover gasket and re-assembly of the timing cover while observing the appropriate torque specifications. I do not have these numbers or the torque sequence in my possession, but I am sure they can be found with little effort.

I did not know about this timing cover issue when I installed my 4.2L. I am taking a chance each day I drive my car. As soon as my beater is fixed-up, I will tear my engine apart to fix the timing cover.

When you buy an engine, get all you can get with it. Even the accessories… Some of them can be resold for good money if the yard lets you keep them. You will need the intake tube and throttle cable brackets. As well as the wiring harness—you’re going to chop that one up.

OK, so you have a 4.2L. Here are some things you will need to complete the swap:

2001 V6 Mustang oil pan
2001 V6 Mustang oil pick-up tube and gasket
F-150 throttle cable (get the one corresponding to your engine year)

Some things I recommend are:

1. Solid rubber motor mounts. The new pan comes pretty close to the K-member. The solid mounts will make sure there is no chance for contact. The stock liquid filled ones have the propensity to rupture and could cause a shattered pan, which means oil starvation, which means new engine.

2. EGR (Exhaust Gas Recirculater) hole plug (1/2 inch pipe plug fitting). This is available at your local plumbing/hardware store. I deleted EGR from my engine and I passed emissions (numbers later). Deleting EGR requires the custom chip to have EGR functions deleted. With this plug, you will be able to use your stock 3.8L exhaust manifolds without EGR. If you choose to keep EGR, you’re on your own! You’ll be bending pipe and taking a lot of aspirin.

3. V8 cat-back or better. Upgrade your exhaust!! You are gonna make more power than before. You better free-up the exhaust to prevent damage and to realize full potential. Be sure to plan ahead. If you are going to run a blower set-up, it may pay to over-size a custom exhaust setup so you don’t have to pay again later (like I did). If staying NA, 2.25” into single 3” should be fine. Also, consider porting your stock exhaust manifolds.

4. New water pump and radiator. Chances are your 3.8L has overheated at some point. Now is a good time to look into a new radiator. Griffin Radiators makes one for ’93 5.0 T-Birds that will work great (automatic) for the V6s. I am running a new stock model and have had no problems yet. You never know the condition of the water pump on a recycled truck engine, so it is good be on the safe side and replace the water pump on your new engine prior to installation. Obviously, replacing the thermostat is a good idea as well—especially if your chip will have the 2nd Gen calibrations on it.

1,013 Posts
Discussion Starter #2
The old stuff…

You will be using a lot of the old sensors off of your 3.8L, so don’t junk it just yet! I won’t cover engine removal because it is pretty straight forward. Just be sure to remove the radiator fan and radiator to allow for some working room and to prevent damage to these items. Find a tool rental shop and get an engine hoist or cherry picker after all the electrical harnesses are disconnected. Keep track of your vacuum line routings and make sure you disconnected O2 sensor harnesses and exhaust manifold collectors. Most important of all, please be safe! Use jack stands and have someone help you when pulling the engine.

You will be using truck #19 injectors unless you choose otherwise. If you are going with a blown setup, then upping the injectors may be a good idea—this also means custom chip programming. Your stock fuel pump will be OK for a stock 4.2L engine.

IMRC and Split-Port intakes

Intake Manifold Runner Control is a device which comprises the most important aspect of the split port engines. The split port intakes found on late V6 Mustangs, V6 F150s, and late Windstars have 2 sets of runners on them. One set is long, allowing for optimal low-end torque. The second set is short to provide air for upper-RPM horsepower. The picture below shows the engine installed with the truck upper in place. Notice the 12 runners.

Some ‘99+ V6 Mustang engines have IMRCs and some only have the split ports with no IMRCs. All of the 4.2L V6s have IMRCs. IMRC is comprised of 2 vacuum actuators, and a pair of rods which open the secondary runner (short runner) butterflies. If you choose to remove IMRC you will loose a considerable amount of low-end torque—essential for our heavy cars. The numerical figure is unknown, but I will find out as soon as I get my car on the dyno. There are arguments regarding flow improvement in upper RPMs with IMRCs removed entirely (rods, butterflies gone), but the sacrifice of low-end torque is too much of an issue in a NA MN-12. Bottom line: Keep the IMRCs and make them work appropriately!!

Engines with IMRCs will have closed IMRCs by default. At high RPMs, a vacuum switch opens and the vacuum actuators activate; secondary runners open. The IMRCs are located in the lower intake manifold. The actuators are located at the rear of the intake and can hardly be seen on an installed engine. Because the IMRCs are on the lower intake and not the upper, there is some flexibility regarding which upper intake you can use. I chose to stick with the truck upper intake for several reasons which will be discussed later.

MSD RPM Switch

If you use a truck EEC and wiring harness (harder way) you do not need to worry about making the IMRCs work. If you go the way I did, the IMRCs become a slight issue. I kept the stock 3.8L computer so I did not have provisions for the IMRCs to operate. The solution was to purchase an MSD RPM activated switch (available from Summit) and a selection of RPM pills. Choosing the correct RPM switch setting will depend on your mods and is best done on a dyno. Since my car has not yet been on a dyno, I based my RPM selection on several runs at the track. I decided the 3400 RPM pill was best (IMRCs open at and above 3400 RPM). I am sure that since I have moved to lower altitudes and have since upgraded my exhaust that this RPM setting is not necessarily optimal. Like I said before, the best way to choose is by using a dyno. On the dyno you’d do one run with the IMRCs closed and another one with them open during the whole run. Overlay the two dyno graphs and the intersection of the curves will be your RPM pill point.

The MSD switch is a negative trigger switch that can be wired to a Bosch style relay to become a positive switch. The vacuum solenoid I used, which came with truck engine, draws a relatively low amount of current. How do I know? I am running the MSD switch as a negative trigger straight into the solenoid. So far, the switch has not burned out. See the device below.

The instructions included with the MSD switch are pretty straight-forward. You hook it up to the ignition coil (located on the inside fender just below the stock air box’s location), and a power source and ground. The switched ground wire is then connected to the vacuum switch. The other end of the vacuum switch gets a 12+ source (fused). I wired a LED to the same switch so I had a visual indicator of my IMRC’s activation from inside the car. The picture below shows the vacuum switch temporarily places on the passenger shock-tower (that’s an alarm siren on the left).


If you want to use a ‘99+ V6 Mustang EEC with IMRC controls, keep in mind that they have a returnless fuel system. This means that you would need a Mustang fuel rail and programming. You would also have to make sure everything is taken care of on the pump side of the equation. If you are going to switch EECs, you are better off keeping the return lines and using a truck EEC.

1,013 Posts
Discussion Starter #3
Choosing an Intake

This is probably the most important decision when it comes to the swap. There are three intakes that will fit the 4.2L split-port engine.

-Truck Intake-
First and most obvious is the truck intake. The problem with this intake is clearance. It will not clear a stock hood and doesn’t clear the 3” Cobra R hood with the IAC (Idle Air Control) in place.

Although there may be a way to relocate the IAC or use a throttle body with IAC incorporated in it, I chose to leave it where it was and cut a hole in my hood. It is not the perfect aesthetic decision, but it’s functional. Exposing the IAC to the elements has not been a problem thus far.

Later on I intend to add a little bulge to my hood so it will cover the IAC. The biggest concern is the IAC harness, which can be scuffed or crushed if there is not enough clearance. The throttle linkage comes close to touching the hood as well, so one of the layers of fiberglass (invisible from outside) was removed from that area as well. The rubber intake elbow I used will take some punishment until I add the bulge to the hood. I will also be fabricating a custom intake tube for the application using close-radius 3” U-bends from an exhaust shop.

Aside from the clearance issues, the 4.2L truck intake was the easiest to adapt to the car. By using this intake, I was able to preserve the 3.8L distributor (see below).

-Mustang Intake-
The ‘99+ V6 Mustang intake manifold will surely clear the stock hood on an MN-12. It would have been the ideal choice for this swap except for the fact that it does not clear the distributor. This causes a whole series of complications since it means that you’d need to switch to a distributor-less ignition system unless your car already comes with one. The ‘96+ V6 T-Birds and Cougars come with DIS and will allow for the use of this intake. The ‘94/’95 California V6 MN-12s also have DIS, thus can use the Mustang intake as well. The solution for someone who has the distributor but wishes to use the Mustang intake is to obtain a DIS ignition system and transplant it to the car. If a truck EEC and wiring harness is being used, then this is not an issue. Just be sure to keep those coil packs and keep in mind that you will no longer be able to adjust the timing on your own.

-Windstar Intake-
The Ford Windstar van has a compatible intake. Nobody I know has actually installed one on another split-port engine. The arrangement of the Windstar intake is much like the truck intake but in a smaller scale. The other difference is that it is made of plastic. This could be good since plastic does not conduct heat like the aluminum intakes do. It could also be bad since it poses a limit in durability. Smash the hood down hard on it and it may mean purchasing a new intake. Also, choosing the plastic intake would limit your porting options. Whether or not the Windstar intake clears the distributor and the Cobra R hood has not been determined.

Sensors and Harnesses

The sensor transplants should happen when both engines are out of the car.

The rule of thumb is to compare the two engine side-by-side, and if they have sensors in corresponding locations, swap them. The only sensor I found that did not have a location for it in the truck engine was the ACT (Air-charge Temperature) sensor. In the 3.8, the ACT sensor was located toward the back of the lower intake manifold. If you don’t find one there, don’t panic. Not all 3.8s have them. Some may have the ACT sensor in the air filter box. If this is the case, keep the sensor where it is. If it’s in the lower manifold, you’re gonna have to drill and tap your upper intake. Please take your sensor with you to the hardware store and make sure you find the correct tap to match it.

I drilled the hole in the upper truck intake toward the back of the passenger side plenum. Here it seems like the sensor would get an accurate reading without being in the way of air-flow. Once the hole is appropriately tapped, use some Teflon tape on the sensor threads and screw it into the upper intake. Once this is done be sure that you’ve cleaned the upper intake thoroughly by whatever means necessary. You don’t want your engine to suck in those little metal shavings when you start it up.

The adapting of the wiring harness should be done when the new engine is in the car with the upper intake manifold off. COVER the lower intake so no debris falls inside. If you drop anything in there, you are going to have to take the engine out and apart! Please get some aluminum foil and wrap the lower intake to prevent anything from falling in.

The stock 3.8 engine harness is kept pretty-much intact except for the TPS (Throttle Position Sensor) harness and the IAC harness. The injector harnesses were a tight fit on my car, but some extending would allow for more flexibility.

You are going to use the truck’s TPS and IAC plugs and harnesses in this swap, so make sure that you cut them with enough slack to splice them into your current wiring harness. When you do splice and extend, make sure to do it right! Solder and shrink-tube it! IF you choose to use crimp-on spade connectors, solder the terminals to the wires after crimping.

Now that you are installing a larger engine, you may want to upgrade to a larger MAF (Mass-airflow sensor—if you didn’t know what this is, then you should not be doing this swap on your own). Both the 80mm LMAF (Lightning MAF) and the late Mustang GT 80mm MAF will be adequate for the swap. Both of them are fairly inexpensive and perform as well (if not better) than the aftermarket competitors. Lately, people say that the Mustang GT MAF is a better choice. This is mainly so if you plan to stay naturally aspirated. I chose the LMAF before the GT MAF hype and it is working perfectly with my NA setup so far. Using the GT MAF does NOT mean you can’t supercharge later. Just know what you want before you spend your dough.

When installing the new pig-tail harness in place of your old one, just follow the primary color schemes on the wires. For example, the black wire with the green stripe connects to the black wire; the red with the yellow stripe connects to the red wire. It’s easy as long as you do a good job with the splicing!


The truck engine’s fuel rail is on the opposite side of the engine bay in comparison to the 3.8L. This means that you will need to extend the fuel lines to the connectors. I’m going to leave this to you since you will need to decide whether or not it will be worth it to replace the whole thing with new lines and fittings, or if you should extend the current lines. If you do extend them, please be smart about it!! A leak may result in a fuel fire and your subsequent death!! On a brighter note, the fuel line fittings plug right into the new rail after extending.

Cooling System

The heater hoses are a PITA, but with some patience it will all work out. The stock hard lines will have to be ditched for some flexible heater hose. You are going to need a ton of hose clamps in all sizes and some fittings to splice the hoses. The device which resides near the top of the water pump (I’ll call it the T-pipe) needs to be cut and rotated to fit in this new configuration. The flat appendix, which aids in holding it down, needs to be modified as well. You are just going to have to be creative and patient. Once it is in the position you want, you will need to pull it out, cover the insert with high-temperature sealant, and re-insert it. Once it is in there, you will need to hold the appendix down but you will find that the bolt and washer no longer reach is. You will need to go to the hardware store to find some large washers that will make this possible. It will make sense when you see it.

In the picture above you can see that I zip-tied the hoses together so they would not shift-around under pressure. They look like they are close to the belt but they really aren’t. But if you do omit the zip-ties, they will get caught in the serpentine belt. Trust me. In the same picture you can see the EGR delete plate I fabricated with a piece of sheet metal and some sealant.

The only modification necessary to use your new engine with your radiator is relatively easy. You are going to need a short length of 2.25” stainless steel pipe and an F-150 V6 upper radiator hose. You are going to cut the new hose as indicated in the picture and extend it using the pipe and some hose clamps.

You will find that the radiator fitting is a little small for the new hose. Cut-off a small section of the old radiator hose and slip it on like a shim. Slip the new hose over it and tighten it down with a hose clamp. The stock lower radiator hose will work on the 4.2L but now is a good time to replace it.

The cooling system is crucial to the longevity of your engine. Please check it periodically for leaks, low coolant, and loose clamps. Heat damage is not covered by most warranted recycled engines.

1,013 Posts
Discussion Starter #4
Vacuum System

At this point, you may want to consult a Hayes manual. It is not rocket science but it is hard to explain in words. Just make sure all the hoses are accounted for and that the brake booster gets a nice vacuum supply. The IMRCs will also need a vacuum source, but the old stuff from the truck should suffice.


All of your stock accessories should bolt-up to your new engine. Just connect everything the way it was. The water-pump on the truck engine may have a fan attached to it. If you were a good boy (girl) and bought a new pump, all you would have to do is install the old pulley onto your new pump. Be sure to use thread locker and lock washers when installing.

Throttle Cable

This is pretty straight-forward. You will need to remove your old cable from the pedal. To do this, get in your car (upside down) and you’ll see what you need to do. Put the truck one in its place and connect the other end to the throttle body linkage. Now you will find that there is slack. You can loop the cable around the linkage and hook it so it doesn’t slip out, or you can do it the right way and buy a small, self-tapping screw and washer and drill into the linkage to clamp the cable down so it stays taught.
I have been lazy and busy, so I have not yet dealt with the cruise-control cable. That requires removal of the mud guard on the inside of the driver’s side fender.


As you’ve probably seen from the previous pictures, I used a portion of the stock truck intake elbow and a piece of ricer cold air tube—civic tube I found at a parts store. I also bought a cheap 3A Racing filter and modified it to fit the LMAF. You’d be hard pressed to find a better solution.

I removed the rubber insert and marked for the holes on the LMAF. I then drilled and screwed the LMAF onto the filter using self-tapping screws. Also, buy some gasket paper and make a gasket to ensure a proper seal. This is the cheapest solution (better than buying the Accufab adaptor) but I had to expand the area where the air cleaner resided to fit the filter.

Miscellaneous Notes:

When installing your engine, be sure that the torque converter is seated ALL THE WAY on the input shaft. You may think it’s all the way in, but it probably isn’t.

Buy some 1/4” flex loom tubing for your wiring.

Make sure you don’t forget to ground the new engine. There is a cable attached to a motor mount. Go to an electric supply store and buy a 4 gauge splice (mechanical). It does not need to be insulated since it is a ground.

All fiberglass hoods should have hood pins. Period!!! You don’t want your hood flying up against your windshield on your first cruise on the freeway. Trust me. If it’s fiberglass, get pins.

Check your fluids (4): tranny, coolant, oil, power steering.

When setting up your distributor, you are gonna need to remove the cap and rotor, and align your crank with 0’ (top dead center). It is possible to be 360’ off, so if there is no compression on the number 1 piston while turning the crank, you are gonna need to give it another turn. Base timing should be set at 10 degrees.

F-150 plugs are NOT the same as 3.8 plugs. They don’t go as far into the block. Get new plugs, wires, cap, and rotor while you’re at it.

I have not ruined my 7.5” rear-end yet. But with all this additional torque, you’re gonna want to upgrade your differential to a trac-lock unit anyways—so get an 8” with nicer gears.

Half shafts are also weak on these cars. SC half shafts should do the trick, but Raxles offers some awesome ones. I am still running stock, but I won’t be surprised when my toothpicks break.

Happy Hunting!!!

--------------- PJ Hradilek
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