K.J. Jones
November 1, 2007
Paul Svinicki (top), Karl Roekle (right), and Mike Sears (left) of Paul's High Performance assess just how difficult creating the Fox 500 is going to be. An engine swap is a big part of this project, so look for more details on this wild GT 500-engine-in-a-Fox swap in the coming months.

Horse Sense: "Modular" in the popular term "mod motor" refers to one of Ford Motor Company's operation protocols. At the company's engine plants (Windsor and Romeo), "modular" stands for manufacturer's tooling that can be quickly changed out to facilitate efficient production of 4.6, 5.4, and other engines.

When you're as deeply engrossed in the Mustang hobby as we are, conjuring up different "wouldn't it be cool if..." ideas probably happens in the same rapid-fire succession as ours-or at least Editor Turner's. We really dig the fact that our tech spectrum ranges anywhere from "wham-bam" upgrades to projects that push the envelope of near-impossibility for '79-'08 Mustangs. We hope that you, our readers, enjoy learning about 'Stangs as much as we do.

Engine swaps are the focus of this report. We'll be talking about tried-and-true conversions such as the 5.0-to-351W or 460 big-block-arguably one of the first few engine-exchange procedures ever performed on Fox Mustangs-and other more radical powerplant trades.

The engine-swap world turned upside down a few weeks before the '06 SEMA show. That's when Chris Whitney of Galpin Auto Sports dropped FRPP's Boss 302-a carbureted, stroked, pushrod engine-between the fenders of an '06 Mustang GT and retained all of the 'Stang's OEM accessories. In the time that's passed since our March '07 cover story on this ride, we've come across a few S197s with some wicked engines underhood.

Many of today's popular engine exchanges involve installing post-'95 modular engines of all types under the hoods of 'Stangs that we now categorize as being early ('79-'93 Fox) models, as well as newer Mustangs (SN-95s to present).

While a cool swap is usually done to add a performance punch to a 'Stang, it's the sight of an against-the-grain bullet sitting between the fenders in "How did they even get it in there?" glory that makes our heart rate jump.

We'd love to be able to provide step-by-step, how-to instructions on the engine swaps mentioned in this story, but there isn't enough room to do so. The purpose of this guide is to let you know about the parts, principles, and some of the critical procedures that comprise a successful change from one engine to another.

Some of you might be thinking, Engine out, engine in-what's so difficult about that? The truth of the matter is there's a lot more involved nowadays than just making a simple replacement. Engines and Mustangs have changed a lot throughout the years. Today's swaps must be approached from more of an analytical perspective than they were in years past-especially when attempting an endeavor that's more over the top than throwing a 5.0 in a former four-banger Fox.

Greg Monroe of Racer's Edge Technology created the "poor man's Shelby GT 500" by putting this Ford Racing Performance Parts 5.4 GT 500 engine in a clean, straight S197. The key to low cost is the fact that the car started life with a V-6 engine, not a Three-Valve 4.6. We don't know if the engine trickery affects insurance rates, but we're sure it puts a world of surprise on those who misjudge the car's six-banger appearance. V-6 to blown V-8 swaps such as this one (with S197s) are the newest of the new. We don't have a full checklist on all the procedures for completing it, but anyone who disputes the "cool" of this project should be stripped of his 'Stangbanger's membership card immediately!

The process is no longer about the nuts, bolts, and hard parts alone. Computers, wiring, and tuning play a major role in most popular swaps of the new era, and there are many other parts and procedures that have equally high levels of importance. Cost of parts and labor is also a major point of concern. While some engine swaps can be done cheap, those that involve a lot of fabrication, reconfiguring the car, and time on the dyno getting the tune right, can end up being pricey when all is said and done.

In our research for this report, we tapped into the ongoing discussions in the 4.6/5.4 forums of several popular Mustang enthusiasts' Web sites (www.streetstangs.net, www.hardcore50.com, www.modularfords.com, and www.modularfox.com, among others) and found that a wealth of good information on various flavors of modular swaps is a few mouse clicks away.

Understand that we're going just below the surface of a topic that is huge. We realize there are nuances, tricks, and things to note for any type of engine swap that may not be mentioned in this report. Remember, you're doing something that the factory didn't and doesn't have in its plans for these 'Stangs, so there will be bumps in the road. The sense of accomplishment after a successful swap is a great reward for your hard work.

There are a lot of pluses in taking a 'Stang to the next level with a different engine, as you'll see in the collection of notes we've assembled and the awesome examples of completed engine-swap projects that are featured in this issue.

Fox 'Stang enthusiasts have looked to the 351W for years as an easy way to increase power and torque through an engine change. This in-progress Windsor swap we found at Extreme Automotive features a 76mm turbocharger and ACCEL DFI engine management system. Note the width of the intake manifold, as it differs from a 5.0's. Tubular K-members are recommended but aren't necessary, but understand there may be oil-pan or K-member clearance issues if you choose to use drop-engine mounts. While factory steering gear (rack-and-pinion) is reusable, installing a Flaming River steering shaft is the best bet for alleviating any clearance problems with headers.

SN-95 and New Edge fans have unofficially appointed Ford's 4.6 DOHC '03-'04 Cobra engine as one of the most popular swap engines for '94-'04 non-Cobra 'Stangs. This Terminator bullet, topped with a Kenne Bell 2.2 supercharger, awaits entry into a '98 convertible GT at B&D Racing. Mase Rowland tells us there's a significant amount of wiring that must be reconfigured, for accessories such as a relocated alternator, among others. We also hear that B&D is working with a company on a new wiring harness that will adapt a '96-'98 GT's factory DIS electronics to the coil-on-plug ignition system of post-'98 modulars. Enthusiasts who want to keep their cool will also have to install a Cobra's air conditioning lines and condenser or modify the GT's pieces for proper fit and function. A larger or '97-'03 Cobra radiator and '97-'00 electric fan are recommended. A snake's radiator can also be modified to fit and work in a DOHC-implanted Fox Mustang.

Looking right at home is one of the big criteria that separates a good swap from a so-so engine exchange. This Fox plays host to a Four-Valve Cobra engine that's enhanced with Vortech's S-Trim centrifugal supercharger, and if it weren't for the bling that says "it's custom" in any language, you would think this setup was laid in by Ford. Racecraft's mod-motor-in-Fox-Mustang K-member plays a big role in that. In addition to the blower, custom exhaust headers are the standout highlights that give this 'Stang its "cool." Swapping the DOHC mill and adding a power adder requires a return-style fuel system such as Aeromotive's, or that of a '96-'98 'Stang, which might do you better in the bucks department.

As we explained in our cover story on Don Bowles' '06 race 'Stang, you never know what kind of test bullet the crew at Roush Engineering is going to put between its fenders, as the 'Stang is a rolling testament to engine swaps. This experimental mill, which sucks down E85 fuel instead of traditional race gas, packs enough power to send Don down the 1,320 with low-nine-second e.t.'s without a power adder. What's involved with getting this beast into a 'Stang? We're waiting to find out. When we learn the deep secrets of the experimental engine, you'll be the first to know.

This is the engine that theoretically started it all when it comes to swapping bullets in late-model (Fox and up) Mustangs. The 351W is a natural upgrade for 5.0 'Stang owners who want the torque and horsepower increase that comes with additional cubic inches. Disregard the oil pan in this photo. A Fox-specific pan and pickup tube are required for installation in '79-'93 'Stangs, as well as a flexplate/flywheel or the harmonic balancer (351W is 28oz balance versus 50oz internal balance for an '81-'95 5.0), intake manifold, accessory bracket, distributor, and exhaust headers. Most of the pieces that make up a 351W/Fox Mustang swap package can be purchased from FRPP.

Let's take a brief look at some of the engines for the swaps we're looking at in this report. First, the 351W shares the 4.00-inch bore size and taller deck height of 9.500 inches of the 302s found in Fox Mustangs. A Windsor's block features thicker webbing in its lower half for increased strength, and its crankshaft has a bigger main and rod journals than the smaller engine's crank. In addition to the obvious 49ci gain right off the top, installing a stroked Windsor opens the door to multiple displacement options and insane horsepower/torque gains over an original 302, especially with the addition of a power adder.

While it would've been a cool option, a 351 Windsor was never offered as an available engine for '79-and-up Mustangs. But in 1995, Ford produced a special run of 250 race-bred, Cobra R 'Stangs that were equipped with 351W engines.

The 4.6 DOHC Four-Valve Cobra engine is an aluminum piece (pre-'03-'04) with a 3.55-inch bore and steel-crank and a 3.54-inch stroke. The deck height for Cobra blocks is 8.937 inches. There are two different power/ torque ratings for naturally aspirated Cobra engines. For model years '96-'98 the ratings are 305 hp/300 lb-ft; for '99-'01 they're 320 hp and 317 lb-ft. Thanks to the excellent airflow of their cylinder heads, adding a Kenne Bell Twin Screw blower to either engine will ramp up performance nicely, but sourcing an '03-'04 Cobra bullet and adding the "Kenne," a centrifugal blower, turbo, or nitrous would be a better move. The later snake engine is founded on a cast-iron block and features a steel crank with forged-steel rods. With its Eaton blower, it makes 390 hp and 390 lb-ft of torque.

Four-Valve InTech engines found in Lincoln Navigators have been around since 1999. These engines are popular with the Mustang crowd because of their forged-crankshaft lower end and aluminum cylinder heads. Despite their good cranks, Navi engines aren't blessed with the strongest rods in the world (fracture-split powdered metal), so their horsepower threshold is about 600 at the flywheel. One of the major pieces necessary for a 5.4 swap is a good intake manifold. Experts say the intake from a '99-'01 Cobra is the way to go, so make sure you have a lead on one before starting the project.

This pre-'03-'04 4.6 non-supercharged Cobra engine is popular among Fox owners who want to adapt new-school technology to their old-school 'Stangs. It's also well-liked among 'Stangbangers with '96-'98 GTs, six-cylinder cars, or 5.0-powered SN-95s who feel the need for more modular power. While the swap has a few dicey moments from a Two- to Four-Valve perspective and certain GT accessories require reconfiguring or direct replacement with actual Cobra parts, the swap is relatively plug and play. Dropping this bad boy or any modular V-8 into a six-banger or last-gen 5.0 'Stang is quite the project, as it involves an extensive wiring-harness change, a throttle cable and linkage change, a revamp of the air conditioning lines, and so on. It shouldn't be attempted unless you have a complete donor Cobra to use as a parts source.

An interesting point: As luxo-SUV engines go, 4.6s found in Lincoln's Aviator feature an aluminum intake manifold with variable-length runners, similar to FRPP's FR500 intake. Aviator 4.6s also use the same Four-Valve, twin-cam cylinder heads as Terminator and Mach 1 'Stangs and are good for 302 hp and 318 lb-ft of torque. While flywheel performance for Navigator 5.4 engines isn't overwhelming-260 hp at 4,500 rpm-the 350 lb-ft of torque they pump out at only 2,500 rpm make them a desirable swap option for any-year 'Stang.

The last two specialty engines that we think are great, albeit elaborate, choices for engine swaps are the bullets found in the Ford GT and the Shelby GT 500. The GT's engine is an all-aluminum, dry-sump Four-Valve that's influenced by a Lysholm screw-type supercharger. It also features dual fuel injectors for each cylinder and oil squirters for the piston skirts. It's rated at 550 flywheel horses and 500 lb-ft of torque.

The '07 Shelby GT 500 uses an iron-block DOHC 5.4 with an Eaton Roots-style blower and air-to-liquid intercooler. These pump out 500 hp and 480 lb-ft of torque.

In the same spirit as the 351W-powered '95 Cobra R, Ford produced a handful of specialty Cobra R 'Stangs in 2000 that were powered by Four-Valve 5.4s.

The new swap trend favors modular engines. For those who need numbers to compare against, here's an overview of the crankshaft horsepower and torque that stock 'Stang Two-Valve engines ('96 to present) produce:

1996-1997: 215 hp/285 lb-ft
1998: 225 hp/290 lb-ft
1999-2004: 260 hp/302 lb-ft

We'd be remiss if we didn't mention that the all-aluminum, single-overhead-cam, Three-Valve 4.6 engines of S197s should be considered for swapping into pre-'05 'Stangs. The engines feature variable camshaft timing and make a reported 300 hp and 320 lb-ft of torque.

We're not sure if this is a little-known fact, but '96-and-up Mustangs have a unique security system called the Passive Anti-Theft System (PATS), which can cause problems for DIY engine swappers who aren't familiar with it. PATS is comprised of a trunk-mounted transmitter and an ignition key with a coded chip (arrow) that all work together to protect the 'Stang. When you attempt to start the engine, the PATS transmitter sends out a radio frequency signal that's picked up by the transponder in the key. Once the key's coded chip is recognized, the transponder returns a unique RF signal to the PCM, giving the OK for the engine to start and run. Engines swapped from PATS-equipped 'Stangs have no hope unless the processor, coded key, and transponder package are part of the process, or the PATS system is disabled with a plug-in chip or flash tuner.

Unless you're using a carburetor on your swapped engine-which we'll assume is probably not the case for many enthusiasts reading this, especially those of you who go with a big-dog modular such as the 5.4s-the new engine setup is going to need some sort of management system to control the amount of air, fuel, and spark it needs to run properly.

There is a myriad of add-on and standalone tuning devices and software that will easily facilitate mild-or-wild swapped engines. A plug-in chip is probably the least expensive option and will best serve an EFI 351W that utilizes factory EEC-IV programming.

Handheld tuners such as SCT's XCalibrator 2 are probably second on the low-cost ladder, and they're perfect for dialing in the nonelaborate SN-95 and New Edge mod-motor swaps that retain EEC-V electronics. While '96-'98 processors can all be used and manipulated for proper functionality, the '98 Cobra coupes have a PCM that's preferred by many technicians who perform Cobra and 5.4 swaps. The Snake's "AOL2" box is return-style fuel system ready and apparently has larger, faster processing capacity and speed than other PCMs, which makes it receptive to tuning changes.

Editor Steve Turner initially selected a '98 Cobra's electronics system as the engine management gear for his Fox 500 project car ('88 T-top LX). Steve and Paul Svinicki of Paul's High Performance are now of the attitude that the hatchback 'Stang's transplanted Shelby GT 500 engine can be operated with all of the Shelby's factory electronics, including the drive-by-wire system, which will be cool if they're able to pull it off.

Standalone ECUs and wiring harnesses are typically applied to hardcore swap applications. FAST's XFI system, ACCEL's DFI, and the new eMS-Pro from Spectre Performance are all worth their cost, as they'll alleviate the issues that go hand in hand with using a factory processor, mass air sensor, and wiring.

An efficient exhaust system is critical to the overall performance of a swapped engine. Naturally, with the 351W procedure being the oldest, there are several good header options on the market from FRPP, BBK, Hooker Headers, and other exhaust manufacturers that provide excellent expulsion of spent gases and maximize the torque value of a stroker- or power adder-assisted Windsor.

The 4.6 and Navigator crowd is limited to 1 5/8-inch short-style headers or stock Cobra exhaust manifolds for a Fox application (which may require some modifying), but full-length and mid-length tubes are available from Hooker, Bassani, JBA, Kooks, and most of the major header manufacturers for Four-Valve '96-'04 'Stangs. The mid-length, 1.625-inch SN-95 headers can be finessed into a Cobra-swapped Fox provided the chassis is laser straight and an SN-95 K-member is part of the swap package.

Packing loads of power without letting on that you're doing so is an important aspect of an engine swap. For pushrod projects, Holcomb Motorsports offers solid drop-engine mounts (PN HPM6000BZ; $69.95) that will lower your new Windsor 3/4 inch, providing an ample amount of clearance for keeping a stealth, stock hood on your 'Stang.

We're not trying to sound like a broken record, but it's important to remember that some facets of an engine swap are similar to the "square peg round hole" theory. In this case, the difference is that the seemingly impossible can be accomplished, but it requires a lot of thought and patience.

Keep in mind that we're focusing primarily on the changes and procedures that take place in a 'Stang's engine compartment. Swaps can also affect other areas of the driveline such as transmission position, driveshaft length, and in some cases, the rearend's horsepower and torque threshold.

Clearances will be critical for the modular exchanges in '79-'93 'Stangs. Navigator and Cobra engines are considerably wider than Windsor engines, especially with their Four-Valve cylinder heads. The large size makes for a tight fit in areas such as the master cylinder, so if retaining power brakes is desired, a hydraboost setup from a '96-'98 Cobra will be necessary. The hydraboost is a master-cylinder assist that operates by hydraulic-fluid pressure from the power steering system as opposed to vacuum pressure.

If you insist on using a stock K-member for a Cobra-to-Fox engine swap-and we can't fathom why you would, as there are plenty of great options available-any '96-'04 engine cradle assembly will work. The rear mounting holes in the K-member must be modified, and the stock lower control arms must be repositioned rearward to ensure that the wheels will sit in the middle of the wheelwell. Going from Two-Valve modular to Four-Valve modular is no problem, as the engines share the same mounts and don't require special K-members. On the painless tip, AJE Racing and Maximum Motorsports offer mild-steel K-members for installing pushrod or modular small-block Fords in '79-'04 'Stangs. AJE now offers swap K-members for either chassis that feature a standard barrel mount on which any type of engine mount (351W or modular) can be affixed.

We advocate return-style fuel systems that include a good pump, regulator, rails, and 1/2-inch lines for any type of engine swap. A return-style fuel setup is efficient, and it's the best way to eliminate fuel starvation and detonation-especially if a power adder is part of the program. Return-style fuel systems were standard equipment on EFI V-8 Mustangs from 1986 to 1999, so some of the OEM equipment may be useable, depending on how radical the project is.

Here's an example of a hydraboost master-cylinder setup from a '98 GT. This system is a "must-have" for 4.6 and 5.4 DOHC swaps in Fox Mustangs. It's a marked improvement over stock brakes and provides ample clearance for a big modular's wide DOHC cylinder heads. Installing this piece on a '79-'93 'Stang requires drilling only one new hole in the mounting plate just above the plate's lower-left hole. The hole lines up with the vacuum booster's mounting location, as well as fabricating high-pressure fluid lines. Editor Turner is employing a trick Fox-to-hydraboost conversion system from Hydratech Braking Systems (www.hydratechbraking.com) on his Fox 500.

The 5.4 engine's taller deck height poses a problem when it comes to installing one in an SN-95 or New Edge 'Stang. A cowl hood from Cervini's is the best bet for circumnavigating the closure problem. Ironically, a 5.4 mod motor can be situated to sit low enough in a Fox 'Stang for the stock, flat hood to be retained. Racecraft's swap K-member makes it possible-we've seen it.