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How to swap an engine

Swapping a Ford "Modular" engine series into an early Mustang

This is one of our specialties; we've been doing it longer than anyone out there. While the information presented here will obviously be tailored to installation in a vintage Mustang, you will find that the majority of it will apply to just about any classic or custom vehicle out there. Whether you are swapping in a 4.6l SOHC motor or a supercharged DOHC 5.4l, the Modular or "Mod" motors are all virtually the same and you will find that most of this info will be useful no matter which exact engine is going into your project. Please note, this is by no means a complete or step-by-step manual, this page is intended as a general guide to answer some of the most common questions we receive about doing these conversions.

You can check out this page in our catalog for links directly to many of the parts we use most in these conversions ourselves.

Chassis/Suspension - aka "Fit the car to the engine"

This is the number one hurdle with these swaps. These engines are physically quite large in both width and height - fortunately depth is rarely an issue. An early Mustang engine bay is tight - roughly 25 inches wide between the shock towers. At 30 inches wide, that makes a DOHC an impossible task to fit without major surgery. By far the most common (and usually cost-effective) way to solve this is by going with a Mustang II-style front end as it rids you completely of your shock towers. leaving plenty of space behind. There are a number of other excellent suspension alternatives that will do this but they are all similar in concept and the level of modification that needs to be done to the car.

    A quick note on "Mustang II" style suspensions! For those new to the world of hot rod suspension - regardless of what you might thinkg, a Mustang-II style suspension setup (at least with regards to this article) is NOT a bunch of cobbled-together parts out of some mid-seventies economy car! This refers to an entirely new, modern engineering approach to a type of suspension system made popular on the "new" Mustang II in 1974. What was special or unique about the setup was that it was essentially a self-contained coil-over-shock system based on a crossmember, upper and lower control arms, and a rack & pinion steering gear. The design of self-contained, tightly packaged system lends itself very well to the hot rod and custom car industry as it is very easily adaptable to almost any chassis. Most modern interpretations of the system incorporate tubular control arms, a coilover shock design and computer designed crossmembers to maximize strength. Since the overall design has been so popular and the components standardized, there are countless upgrades and custom parts available for those going this route.

Fortunately, while still snug, the engine and transmission combination fit quite well with these setups. When you take your time to set up the motor and transmission to maximize the space, you'll find that they seem like they are made for each other. We have found that some suspensions tend to fit better than others given the tight quarters. Our favorite for the Mustang II style setups is the RC Motorsports kit, as their crossmember is well-positioned and notched as needed to clear the oilpan. This kit is able to be ordered with modular motor mounts, which is a nice bonus instead of having to build your own (see details in mount section following), has a rack that permits good oilpan room, and a straightforward installation that is well engineered. These guys have been building conversions for the early Mustangs for many years and have it down well. For about $2700 (at the time of this writing) you get an entirely new front suspension with tubular control arms, adjustible coilover shocks, 11-inch disc brakes and power rack and pinion - A great package deal. For those really wanting to go nuts, there are a handful of complete chassis available such as the Art Morrison Max-G chassis.

    For those with 67-up cars doing SOHC 2v swaps, there is hope if you aren't wanting to go all the way with your front suspension. With a little trimming. the narrower SOHC engine will actually fit down in between them with about 1/2-inch to spare on each side. We have in the past sold bolt-in custom motor mounts available for this swap, and combined with the rear crossmember you can make it work with minimal fabrication. At this point all of the off-the-shelf mounts we know of have been discontinued, as the 2v swaps have dwindled in popularity so you'll have to build your own. For non-A/C cars, the heater motor will have to be flipped over (this can be done by pulling the heater box and unbolting it), and when the heater box is reinstalled we recommend using four nuts to space the box 1/4-inch further back from the firewall just for a little extra room. A front-sump oilpan and pickup will need to be used, we sell the Canton 15-790 and pickup as our favorite for the swap.

A few people have asked about transmission fitment in the tunnel. We have had no trouble fitting the T-45 and Tremec transmissions. With the motor dropped down in position, leaving about 1/4 inch clearance above the transmission is plenty and we have been able to get good driveline angle. However, for those doing a T-56 conversion, you may find that modifying the tunnel to be a necessity - They are a fairly large-diameter transmission. The easiest method we've found is to split the area horizontally down the side of the tunnel, "lift" the section up to where it needs to go, and then fill it with a strip of metal down each side.

Brakes - Master Cylinder & Booster

This particular item is important due to the tight clearances in the engine bay. If you are running non-power brakes, the hurdles will be minimal. Going with power brakes does complicate things a bit, but as long as you use the proper parts it's not a major ordeal.

    Note on the master cylinder: Regardless of power or manual, you'll need a master with drivers-side outlets, otherwise your brake lines will head straight into the valve cover. Modern aluminum masters generally have a thin body with a plastic reservoir which work great and sit above the cover. Our favorite for these swaps is the 1997 Explorer master cylinder, and it can be had out of the box in either 4-wheel or 2-wheel disc varieties. Just make sure you opt for a "new" one and not a rebuild, as the rebuilds will not usually come with the reservoir. Also, many aftermarket brake kits will come with a master which you may or may no be able to use, check on the specifics when ordering.

We have begun seeing more and more of these cars going with a hydroboost conversion - This setup is hydraulically assisted and is powered by your power steering pump. There are now aftermarket kits on the market and most will have good clearance with the engine swap. These have the advantage of not requiring vacuum to operate, but do need a steering pump to function. We usually go for the standard vacuum booster as with the right kit, they nestle nicely behind the cylinder head, plumb easily (one vacuum hose!), and generally look like they belong. The hydroboost units require routing a number of hydraulic hoses to and from the unit and tend to stand out more, but they certainly have their place in certain applications. One of our favorite power conversion kits is the MustangSteve kit. which also happens to be available as a complete cable clutch conversion system also (very handy with the 5-speed, see clutch section).

One of the first things people seem to notice when looking at these conversions is how tight the clearance is to the master cylinder. Most all of the suspension kits use a pretty tight poly mount that leaves very little movement in the motor, so anything around 3/16-inch or more should leave plenty of room for what little engine movement there is.

Engine/Tranny Setup & Mounts

All of these conversions definitely have their share of fabrication and setup work and the mounting of the engine/tranny combo is no exception. There are a few prerequisites before starting the setup. First, bolt in your steering rack and vacuum booster - You can leave the master out to start, but have it handy. Second, the motor and transmission go in together as a unit.

As far as how to position the motor/tranny combo, there are three general guidelines to try and follow when doing your mock-up: Position the shifter in the right spot. get the motor within 1/2-inch of center in the engine bay, and set the motor as absolutely far down in the hole as you can - The oilpan should be no more than 1/4-inch off the rack (and this may require some notching of your crossmember). Minding the brake booster clearance, this should get it sitting right where it wants to be.

If you have the late-model factory transmission crossmember you can modify it pretty easily to bolt in. If not, we should have bolt-in replacements available by the time this information is live. Having this piece available can make your motor installation easy, as you'll be able to set the transmission position and have one less adjustment to be making.

The motor mounts will usually come with your suspension as a do-it-yourself kit, consisting of the motor-side pieces, the bushings, and the stands. We like to use shims to get the motor positioned just perfectly above the steering rack and then build the mounts in place, accounting for the small amount of sag that the engine will have once its weight is on the bushings (minimal). Keep in mind that the driver's side must have room for the steering stalk to pass through (which should be in place during mockup) but can make things difficult when trying to fabricate the mounts. You can find a few motor mount photos here and here and here and here. It works best to bolt on the motor plates and set the engine in the bay, using shims or blocks to position it carefully on the crossmember. Then, take your time mocking up the mounts. Once you've got it perfect and everything tacked in place, unbolt the steering rack, tack weld it on the frontside and carefully pull the motor back out for final welding. It's a process, but you end up with a great fitting setup in the end.


Most of these conversions are performed with a manual transmission. The pre-2005 transmissions are all designed to use a cable-style clutch system, which is significantly more simple and efficient than the old mechanical setups with rods, levers, springs and pivots all over the place. As mentioned previously, one of our favorites for those doing a power brake and cable conversion are the MustangSteve kits. as he incorporates both the power unit and cable conversion into a nicely packaged ready-to-go unit. If brakes are not a concern of yours, our other popular kit is the Modern Driveline conversion. It is a nice bolt-in system that doesn't require any fabrication work and we have had good success with these as well. All of the manual transmissions from 2005 on operate the clutch with an integral hydraulic throwout bearing. What was in the past considered a last-resort and usually problematic aftermarket solution, the latest aftermarket and OEM hydraulic throwout bearings are of great quality and don't require routing a cable through the engine bay. There are a number of firewall-mounted hydraulic clutch master cyliders available, and for those with some creativity and fabrication skills, you can actually use the factory matching master cylinders out of the late model cars.

When the drivetrain is positioned correctly, with the cable operated transmissions the shifter is in the perfect spot just as original - which becomes essential when working around a console. One thing to keep in mind is that the forward location of the shifter in the old cars is nowhere near the more rearward position of the new cars, meaning that the late model shift handle will not work (unless you have extremely long arms). To solve this problem, the easiest method is to use a T-5 conversion handle that duplicates the original shift levers, but has the mounting provisions for the late model transmission. We have these in both the 65-67 style and 68 style. either of which will of course work in any year or model car. On the later 05+ manual transmissions, the shifter was mounted to the body of the car rather than being built-in to the transmission, and is quite a bit further rearward. We have had great luck adapting these factory shifters to the early cars, but it does require some tunnel modification as the shifter will end up quite a bit further back than the stock unit - In a much more user-friendly location.

Ford uses a couple different style of fuel regulation on the modular engines, so you'll have to build your fuel system depending on what engine you are using. There are two basic setups; a return-style system and a returnless. In a return style system, the fuel is pumped from the tank and through the injector rails to a regulator. This device is basically a spring-loaded diaphram that regulates the pressure fed to it, and bleeds off the excess to the return line that goes back to the tank. This style system was used on all of the 5.0l engines and the first generation of the 4.6l motors. This type of system is easy to setup and requires no computer or electronic controls, just two fuel lines (one feed, one return) and a mechanical regulator. It is commonly used when doing any sort of EFI swap, be it factory or aftermarket as it can be easier for the do-it-yourself mechanic to control.

As technology progressed and computers began to take over more of the operations, Ford began moving more to a returnless type system. As with the return-style system, fuel is pumped from the tank directly to the injector rails. However, instead of a pressure regulator at the end of the rail there is a pressure sensor. The computer uses this sensor to regulator fuel pressure by actually controlling the fuel pump itself, regulating its output to deliver the pressure required. A returnless system can be converted to a return-style simply by adding a regulator and return line. However, the computer will need to have tuning adjustments made to prevent it from attempting to control the fuel pump.

For the actual fuel pump, there are a couple of possible ways to go. EFI systems typically run in the 30-50psi range (high pressure), while carbureted cars run in the 5-10psi range (low). Most older cars run a mechanical pump attached to the engine which is only capable of about 7psi, so you'll need to install an electric pump. One of the quickest and easiest is to run an inline pump placed in the fuel line between the tank and engine. This does have its downfalls, however -

they are typically fairly noisy, no matter how well one tries to isolate it, they are prone to cavitation from having to pull the fuel up from the tank, and can run hot from continuous duty. The solution is to run an in-tank pump, as most modern cars do for a few reasons - this helps keep the pump cool, being in the tank keeps it quiet. While there are kits to install an inline pump in your original tank, they can require some fabrication work and generally welding and fuel tanks do not go well together without very specific preparation. On race cars and for those willing to spend a little extra money a fuel cell with the pump built in is a great way to go. We carry the Fuel Safe brand which we have had great success with, they make an excellent unit that is a drop-in replacement for the Mustang tank. However, these can be very expensive - The best alternative for most street cars is the Aeromotive Phantom in-tank system. This is a slick retrofit for your factory tank that puts a high quality pump into your factory fuel tank, giving you all the benefits of a modern in-tank setup with 6AN connections and a foam slosh baffle.

For those running a return-style system without a fuel cell or in-tank conversion like the Phantom setup, you'll have to plumb the return line back into the tank. The easiest route can be to hook into the fuel tank drain bung, however this being on the bottom of the tank means it's a pretty low-hanging mount. In addition it will tend to stir things up on the bottom of the tank that otherwise are undisturbed - Not a huge issue, but in a 40 year old tank, make sure you have a good filter on it. The other easy way is to modify your sending unit by welding/brazing in an additional fitting. This can be done by taking a short length of fuel line tubing, drilling a hole (use a step bit; a standard bit will tear up the sender), and brazing/welding/soldering it in place.

Fortunately this is an easy one. The factory manifolds will fit fine. We have found that most shorty headers designed to fit late model Mustangs will also work fine, as they tend to hug the block fairly tight. We like to use the Ford Racing headers whenever possible, as they have excellent fitment and are leak-free.

You will need an o2 sensor in each pipe immediately following the socket or flange. The Coyote 5.0l engines have the o2 sensors located in the factory headers, so nothing additional is needed in the exhaust system itself. However, the older engines had them in the mid pipe so when possible, we will salvage the first 8 inches or so of the donor car's exhaust which will have the proper flange to made to the manifolds, as well as incorporate the bung for the o2 sensors. If you are starting with a crate motor or do not have this piece available, a good exhaust shop will either have the correct flanges or be able to make them, complete with o2 fittings.

Beyond that, the exhaust is up to you. There is plenty of room under the car with the late model transmission to run any sort of exhaust you like; these motors have a great sound to them when opened up without the emissions equipment required on the original car.

Cooling System & Plumbing

Going to a larger capacity radiator, preferably aluminum, is a recommended upgrade. If you are currently running a wide core (24in) radiator, and it's a 4 core, you've got more than enough capacity. However, the late model engines are designed to run at higher temperatures than the old engines and demand better radiators that will stand up to the heat. For the modular engine, you'll want a radiator with a right-hand inlet (upper fitting on the passenger side), and left-hand outlet (lower fitting on the driver's side). This is the most common setup for most cars, and often times you can buy an aftermarket unit designed for your car with the connections in the right places. For the early Mustangs which never came with the larger radiators, your best bet is to either use one designed for a 67-70 car or swap in a custom unit instead.

The radiator plumbing can seem a bit confusing at first, but it is not a major task to get it all working as designed. The upper hose is simple, connect it straight to the radiator as usualy. The other two hoses (yes, two) are what causes some confusion. Many of the modular engines will use a small external aluminum housing that has four hose connections - This is the thermostat housing. The principal behind this is that water comes in from the radiator. If the engine is cold the thermostat blocks off the cold water intake from the radiator, and instead pulls it from the top of the engine, recirculating it for faster warmup. Whenever possible we recommend running this part as it ensures proper operation of the system and promotes fast warmup, which these engines need. The two large engine hoses connect to one side, the other large fitting goes to the radiator. The last remaining smaller fitting would normally go the factory coolant tank, however on most conversions this is not used and can be blocked off by pulling out the hose nipple and pressing in a 3/4-inch freeze plug.

An electric fan conversion will be required. If using an aftermarket direct-replacement radiator, chances are you can purchase a fan kit that will fit it. If swapping in a late model radiator, use a late model fan that will bolt right on. Some of the swap wiring harness kits will allow the engine computer to control the fan and can be wired as such. If you are not using the computer to control it, the answer is a standalone electric fan thermostat which will turn the fan off/on based on the radiator temperature; if you are running air conditioning be sure to use one with an A/C override provision. This allows a signal to be fed from the A/C compressor that forces the fan on when the A/C is running.

For those doing a keep-it-simple swap, the easiest method for intake is just to use the factory tube and filter (airbox or not is your choice). Most aftermarket "cold air" intake kits will also fit and work just fine, and with a little fabrication, a fenderwell intake system can be done. An important thing to keep in mind is that on the newer engines running with the FRPP control pack are specifically tuned for the MAF housing that's integrated into the airbox included in the kit. While you don't need to use the airbox and can build your own intake pipe, the slightest deviation in internal diameter from the factory piece will affect the tuning. A good way around this is to take the FRPP airbox and carefully cut out the MAF sensor portion of the box, which will leave you with about a 5" long plastic tube that you can then integrate into your intake pipe and attach a generic cone filter to. This gives you flexibility of placement and retains the factory MAF sensor exactly as the ECU is tuned for.

Accessory Hookups

This is another common question - how will the accessories work? All of the accessories that come on the 4.6l engine will be used in the swap. If possible when buying your donor engine, get one already loaded with these as you'll have to buy them anyway. If for some reason you are not running A/C or power steering, there are delete kits available to eliminate these.

Alternator: Obviously this one is required by everyone. On the 4.6l engines, the alternator wiring is usually not included with the engine harness as it is a complete system on its own. Fortunately, it's also very simple to hook up - you'll need to make up your own main charging cable from 6 or 8 gauge wire and run a small wire with key-on power to the smaller plug. We use the Ford pigtail which plugs right in to keep it clean. On the 5.0l Coyotes, the alternator plugs into the engine harness and you will only need to add your own main power lead.

Power Steering: This can be handled one of a few ways. The easiest is to call a hose specialist and have a pair made up with the correct ends for your particular pump and steering rack. There are many hose and fitting houses around, the deal primarily in truck & hydraulics, but this is no different as long as they have the right fittings. Often mobile A/C repairmen will have these fittings available and will come to your location to build them. You can also build your own hoses using readily available AN fittings and hose. Unfortunately the wide variety of racks on the market makes it difficult to produce these in a ready-made form, but if you know what to look for, the parts are easily obtainable. Maintain the factory and reservoir (and hose between them!) for a very easy return-side hookup. Remember that the return side is not under high pressure. With many aftermarket racks (such as that with the RC Motorsports kit) you can use a factory late model Mustang hose, it will usually be slightly long but will work.

Air Conditioning: This, like the power steering, isn't actually as hard as it seems. You will need to have the A/C pump manifold altered to add AN fittings in place of the Ford quick-disconnects; we can provide this service as well as the large A/C companies. We have used many Classic Auto Air systems with the 4.6l conversions and they have worked extremely well. When we are installing A/C on a swap car here, we'll order the system with a do-it-yourself hose kit. This will give you extra-long hoses and a box of various connectors and hose ends which you can mock up how you need. Like the power steering hoses, the easiest way to handle this is to find a good mobile A/C service and have them come out and make up your hoses right in place. For the do it yourself types, once it's laid out, mark everything and take it to your local automotive A/C supply vendor to have the hoses crimped - this requires a very specialized tool which most hose and fitting vendors do not have.

Wiring & EFI

Certainly for many this is the most daunting part of a fuel injection conversion. However, if one takes their time during installation and uses quality parts along the way, it is not nearly as difficult as it can seem. The first question we often receive is "Can I use the factory engine harness and wire it myself?" - Technically, the answer to this is yes (for most engines). However, based on our experience, this is a very extensive process requiring advanced automotive and fuel injection wiring knowledge, as well as about 2 weeks worth of time and a 300 page Ford wiring diagram.

For the vast majority of people performing these swaps, the answer is a conversion harness.

    For the 2v/4v engines. the most popular which we use and sell is the Detail Zone kit. This kit is centered around a relay control board which is designed to take the place of the factory relay control modules and manages all of the sensors and power to the computer. This board plugs directly into the ECU with a factory type connector, and all engine components wire to it. The kits are complete with all wiring and plugs needed. Once all wiring has been run and connected. the only wires that interface with the rest of the car is a ground, constant power, and ignition power. The entire system is self-contained and provides an ODB-II connector for diagnostics using a standard handheld scanner.

Where does all this equipment and wiring go? In a coupe, we generally locate it behind the rear seat. You need to have space enough for both the control board and PCM (computer). In a fastback, the large cavity inside a quarter panel works well. Either is accessible for wiring and has enough working room for installation. The door channels will be full in the end, but there is enough space to make it work and do a nice clean job.

    For the 3v engines, the Ford Racing Controls Pack is the way to go. The kit includes a harness that is designed to plug into the factory engine harness (so be sure you get that with the engine), a new PCM that is setup and ready to run (without the anti-theft, emissions and fuel system programming that the stock PCM has), electronic throttle pedal, a Ford Racing intake (may or may not need), and a relay control module that feeds power to the fuel pump, cooling fan, PCM and the rest of the system.

Besides the major topics already discussed, there are a few remaining details worth noting. First, the late model engines (through 2004) use a cable-type throttle. We have found that it works best to use the stock late model cable, as it will hook right up to the engine and is about the right length to work in the car. 1969-70 Mustangs originally used a cable linkage and will basically hook right up to the new cable. 65-68 cars used a lever & rod setup that will need to be changed. You can either do a bit of fabrication work and modify the stock pedal to accept the cable end, or you can start with a 1969 or 70 pedal and modify it to work in the earlier car.

The oil filter adapter can also be a source of headache for some. The modular engines use a bolt-on adapter at the lower front left of the block that integrates the water inlet as well as the oil filter base (or tubing for remote applications). Many of the 2v and 4v engines that shipped in Mustangs orignally came with a large, bulky unit that will work with a remote adapter, but would put a spin-on filter right into the frame rail. If you replace the unit with a Ford part XL3Z-6881-AA. it will put the filter tight against the block and a regular FL-820S filter can be used. You can get this filter under a 2001 F-150 5.4l application.

Instrumentation, for the most part, can be handled just like any other engine. The sensors that wire to the computer are there for engine operation and should not be used for gauges. There are extra ports on the side of the block the oil filter adapter that can be used for aftermarket gauges. Most of the transmissions used behind the modular engines ran an electronic speed sensor. This sensor is usually wired to the computer, but can also be tapped into for an aftermarket speedometer. We commonly use Autometer gauges with the engine swaps which can be calibrated to the stock sensor. For those wanting to run a tachometer, a tach adapter designed for the donor car must be used to generate the signal a tach and read.

Category: Forex

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