KJ Jonesx
April 22, 2012

Clevor Fox

For the pushrod purists, replacing a Fox's 5.0 with a 351W-based engine has been one of the longest-running, easiest-to-do swaps. The feat has been accomplished countless times at this point, and its resultant power and torque confirms the adage that there really is "no replacement for displacement."

We recently took the 351-swap concept a step further; building a 351W-based, fuel-injected, Cleveland-headed, 408 stroker, and installing it in Greg Montoya's '89 Mustang GT.

While this type of swap was once considered "undoable" as an affordable effort, it's now a solid option for making radical pushrod big steam, with parts that are readily available.

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The Originals

Here's a breakdown of some of the pioneering engine swaps for late-model Mustangs, compiled by editor-at-large Tom Wilson. It's hard to process the fact that it really wasn't all that long ago, when these four engine swaps were at the top of the charts.

Pushrod 5.0

This is one of the easiest swaps because readily available, stock factory parts are all you need to replicate a 5.0 LX or GT from a humble 2.3. Furthermore, if you're interested in what the swap will turn out like, just drive a 5.0 Fox. In fact, because there are so many V-8 Foxes still available, our first advice is to consider selling your 2.3-liter project Fox and buy an H.O. as your starting point. It's often the quicker, less expensive, and easier option.

On the other hand, converting a four-banger can be a smart move. By now old Fox Mustangs need everything, so ditching a pile of wasted, puny four-cylinder driveline parts is a no-brainer if you're installing a 31-spline rear axle, T-56 trans, a new suspension, and big disc brakes anyway. That makes this swap especially appealing for race cars and Saturday night shakers--cars that care little about interior niceties and depend more on an unwrecked, rust-free unibody than anything else.

Conversely, if you're going for a clean street car, you're almost always better off starting with the cleanest street 5.0 H.O. you can afford and selling that four-banger your uncle gave you. This is especially true if considering an early Fox with a brittle SROD transmission or 7.5-inch rear axle.

Technically, the V-8 into a four-cylinder Fox swap can be accomplished with little more than a V-8 engine, engine wiring harness and computer, but as the horsepower goes up, so does the need for more robust supporting pieces, such as larger radiators, better clutches, bigger fuel pumps, and so on, so don't overlook those upgrades in your planning.

Pushrod 5.8

When Ford developed the 351 Windsor, it invented the best reason to swap engines-displacement in a compact, affordable package. We're not going to get too deep into the 351 swap from a nuts and bolt standpoint because it's a well-known job and reasonably straight forward. That, and there seems to be as many ways of making a 351 work as there are 351 swaps because the aftermarket is positively dripping with parts.

That said, the only Mustang since the '70s to get the 351 was the rare '95 Cobra R (only 250 were built). That gave us all the parts when dropping one into an SN-95, but you'll need more help in a Fox or New Edge. Start by reading 351 Engine Swap from our May '01 issue. It's also on our website and gives the necessary details. We also highly recommend Maximum Motorsports (www.maximummotorsports.com) K-member for this swap to offset the heavier engine's weight and open up header room. The gain in handling is important, too.

What we'd like to concentrate on is why the big Windsor is such a good swap. Most importantly, exceeded only by the behemoth 460, the 351 offers far more cubic inches of displacement than the pencil-neck modulars or the tightly packaged 302. Even better, the 351 can be built to well-over 400 cubes with passable durability, and those engines pack an immediate low- and midrange torque hit that's a blast to drive.

Windsors are durable, too. Even the stock blocks are notably stouter than 302 blocks, and the heavy-duty FRPP Sportsman and aftermarket blocks are anvil tough. But they aren't big! A 351 poked and stroked to 427 inches is much more compact than a 281ci modular; this makes them far easier to install and work on. These engines aren't overly expensive in near-stock trim, either, although a full-house stroker will add up for sure.

The downside to the 351 is that it's a full notch heavier than the 302, and the legacy Two-Valve pushrod design does not match the newer modular in smoothness, fuel economy, or breathing without good aftermarket cylinder heads. But for quickie street-oriented performance, the easy low-end torque is sure to please; if major power is wanted, there are race heads and big displacement on your side.

Two-Valve 4.6

Like putting a pushrod 5.0 in a four-cylinder Fox, slipping a Two-Valve 4.6 into an SN-95 is simply duplicating what the factory has already built in the Mustang GT. Once again we say you should take a hard look at simply buying a V-8 Mustang as the starting point and selling whatever V-6 car you may already have. That's not always the best move depending on what you're aiming for in the finished project, but it's definitely something to consider.

An advantage to the SN-95 is there are fewer differences between the V-6 and V-8 versions. This is especially true with the '99 and later New Edge cars, which all came with a 3.27-geared 8.8-inch rear axle. The '99 and later GTs all sport coil-on-plug ignition, too. That's one less wiring hassle when wiring in a later modular V-8.

One significant difference is the '94 and '95 GTs, which used 5.0 pushrod engines and classic EEC-IV engine management, while the same year V-6 cars had already moved on to OBD-II electronics with a data port. When the 4.6 Two-Valve went into the GTs in '96, they too were OBD-II cars. Another detail is all manual-transmission, modular-powered SN-95 GTs use a T-45 gearbox as opposed to the T-5 in the previous Fox cars. The meaningful difference is the T-45 has an input shaft that's 5?8-inch longer than T-5. It was needed because Ford actually moved the engine slightly forward in the SN-95s.

Terminator 4.6

At some point an engine swap goes from an interesting challenge to impossible for the home mechanic, and that line lies between the naturally aspirated Three-Valve 4.6 and Terminator Four-Valve swaps.

There are two reasons the exciting supercharged '03-'04 Cobra engines are beyond the capabilities of a home garage enthusiast--the engine's physical size and the complexity of its electronic controls. Together these make swapping the Terminator into an earlier Mustang daunting. While it can be done, it is often too expensive and too encompassing for the average guy.

But as noted, it can be done. On the physical size standpoint, you'll need Hydraboost (or manual brakes) to clear the cam covers, you'll want the Terminator's gas tank and fuels pumps, and you'll find plenty of fabrication work hanging the charge cooler radiator, relocating the radiator, making a rear transmission mount, an so on. Electronically the Terminator wiring runs to the instruments, the transmission, and as far away as the taillights, with GEM and fuel pump modules previous cars don't have.

In short, installing a Terminator in an earlier Mustang is pretty much installing an '03 Cobra's brains and mechanicals into the bodyshell of another car that wasn't particularly designed to accept it. It is definitely a pro job.

All of this adds up. A Terminator engine is about $8,000; the transmission, $4,000. It takes 60-100 hours of pro labor to put it all together, so that's another $8,000 or so, and that doesn't begin to include the upgraded suspension, brakes, blowers, fuel systems, sound systems, and other stuff such massive projects tend to attract.