Displacement Replacement: Swapping Your Mustang's 5.0L for a 351W

Horse Sense: As popular as the 351W-in-a-Mustang swap is, Ford waited until the last year of the Mustang's pushrod engine to offer a production Mustang with a 351. Only 250 units of the '95 Mustang Cobra R were produced with the 351. That R's engine produced 300 hp at 4,800 rpm and 365 lb-ft of torque at 3,750 rpm.

Cubic inches are like money. Having enough to be comfortable is nice, but having a lot is better, and having more than you know what to do with is just right. The 5.0 is a potent engine--just ask any 5.7 Camaro owner--but when it's time to rebuild or you just want that competitive edge, some extra cubes are in order. Yes, there are numerous 302 stroker kits on the market, and they have their advantages (which we'll talk about later). But if you really want to go for the gusto, then you should consider moving to a 351W. It has more cubes in its stock form than you can comfortably--or affordably--extract from a 302-based engine, and you can stroke it well beyond 400 cubes should the need arise.

If you've been thinking about a 351W swap but didn't know where to start, you're in luck. We talked to some of the leading swap experts in the industry.

In the following pages, we'll discusss 351W/Fox chassis swaps and their advantages/disadvantages versus a 302-based build. We'll also clue you in to all the parts necessary to get the job done right--from the oil pan to the top of the intake manifold. Now let's get rich!

As swaps go, the 351W/Fox chassis swap is relatively simple, with no fabrication or butchering required (the same is true with SN-95 cars). The stock motor mounts will work, as will the front cover, the radiator (if you plan to build a mild 351), the shroud, the water pump, the pulleys, and all of your accessories when the proper brackets are used (more on that later). Unfortunately, just about everything else needs to be replaced, which will add to the cost of your project.

Beginning with the bottom of the engine, the first thing you'll need is a different oil pan. The 302 uses a rear-sump pan, while the 351W uses a front-sump oil pan, which necessitates a new pickup. If you're going to limit your driving to the street, FRPP offers a complete oil-pan kit (PN M-6675-A58) that includes a 5-quart (stock capacity) rear-sump pan, a dipstick, a tube, and a pickup. The oil pump and drive are not included, so you'll have to purchase these items separately. For a street application, FRPP recommends a stock-replacement oil pump (available through Melling), while a street/strip engine with looser bearing clearances (0.0025-inch) can use an FRPP M-6600-B3 pump. An FRPP M-6605-A341 driveshaft will work in either instance.

For street/strip applications, Canton offers a rear-sump, 7-quart oil pan (PN 15-670, with a pickup sold separately under PN 15-671). Moroso also offers a 7-quart oil pan (PN 20520) with a built-in windage tray and scraper that fits '81-'97 Mustangs, '81-'88 T-birds, and '81-'86 Capris (pickup sold separately under PN 24514).

The 351W also has a different balance than the 5.0. The 351W requires a 28-inch/ounce unbalance, while the 5.0 uses 50-inch/ounce unbalance. This means you won't be able to reuse your stock 5.0 flywheel or harmonic damper on your 351W. FRPP offers a billet steel, SFI-approved, 157-tooth flywheel (M-6375-A302) that will work. And assuming you wish to use the factory serpentine-belt system, you can use the FRPP steel damper (PN M-6316-C351), along with the M-8510-B351 or C351 spacer, which creates the proper alignment with the serpentine system.

According to Rod Kack at FRPP, you can also use a damper from a '75-'80 302 or 351W engine, but you have to make sure you get the right one. There are two different bolt patterns and three different lengths, measured from the mounting face to the end of the snout: a 3.000-inch with a three-bolt pattern, a 3.400-inch with a four-bolt pattern, and a 3.950-inch with a four-bolt pattern. This last one, according to Rod, is the only one that will suit your needs if you want to retain the serpentine system.

As mentioned earlier, the stock motor mounts--if still in good condition--will work. But, because the 351W is 3 inches taller than the 302 (measured from the bottom of the stock pan to the top of the stock valve covers, the 302 measures 20 3/4 inches, while the 351W measures 23 3/4 inches), you could encounter hood-clearance problems with fuel injection. HP Motorsport offers solid motor mounts, which lower the 351W by 3/4 inch in the engine cradle, improving both hood clearance and center of gravity. According to HP's Paul Brown, you shouldn't encounter any clearance problems down below as long as you're using the FRPP 351 pan, stock crossmember, and rack. Paul also maintains the solid mounts aren't too severe on the street as long as the factory rubber trans mount--or aftermarket polyurethane mount--is used.

In any case, you may still require a cowl hood, so keep this in mind when tallying your expenses. If you're beginning with a car that was originally equipped with a four-cylinder or V-6 engine, or you just want to use stock-type motor mounts, George Klass at Coast High Performance recommends certain Ford motor mounts (PN E7ZZ-6038-E and E7ZZ-6038F). These are factory convertible 5.0 motor mounts that feature more reinforcement and therefore are stronger than standard 5.0 motor mounts.

The front cover from your 5.0 will work, along with the water pump. But if your water pump is original, it's probably not a bad idea to purchase a new unit from FRPP, or aftermarket manufacturers such as Edelbrock, Stewart, or Evans Cooling.

Since we're assuming you've started out with a new or rebuilt 351 short-block, we're not going to talk about camshaft or timing-chain choices, but there is one important detail that bears mentioning. Early 351W blocks are not designed for use with roller hydraulic cams. This leaves you with two choices: Run a flat-tappet cam, or make some changes so you can run a hydraulic roller. "We find that about 50 percent of our customers stick with the flat-tappet cam," George Klass says. "But that limits you to less-aggressive profiles because of the ramp rates [of a flat-tappet grind]." George says if you want to use a hydraulic-roller cam, you can use stock 5.0 roller lifters as long as you run a small-base-circle cam (also known as a retrofit cam), available through a variety of cam manufacturers.

The next step up the ladder is the cylinder head choice. There's no difference here--in aftermarket heads, that is. Any popular aftermarket head designed for the 302 will also fit the 351W, provided the bolt holes in the heads are stepped and can be drilled out for 1/2-inch fasteners. Using junkyard heads and then porting/rebuilding them is another option, but this won't really save you much money over a set of assembled aftermarket heads unless you do most or all of the work yourself. Junkyard heads also won't flow as well as a pair of aftermarket heads.

Again, because the 351W has taller decks than the 302, this places the cylinder heads further apart, which precludes the usage of a fuel-injected 302 lower manifold or any 302 intake manifold for that matter. If you're going with fuel injection, you have only a few manifold choices, according to Ed Marsh at Windsor-Fox Performance Engineering. You can use the FRPP GT-40 setup used on the Ford Lightning or the Lightning lower and a Cobra upper. Other options include Edelbrock's 351W truck lower (PN 3884) with a 5.0 passenger car upper (Performer PN 3822 or Performer RPM PN 7125), and Trick Flow's 351 EFI Manifold (PN 5150000-4), which includes the upper and lower (also available separately). Yes, the 351W truck upper will bolt up to the engine, but it's not a performance piece and hood clearance problems would be extreme, Ed explains.

For racing purposes, Coast High Performance offers its 351W EFI Spyder intake, which is a four-barrel Victor Jr. manifold with 1/2-inch fuel rails and a 90-degree Power Elbow that accepts up to a 90mm throttle body.

Now that we've talked about what's necessary to bolt the 351W into the engine bay of your Mustang, we'll discuss the stuff you're gonna bolt to the engine--namely the accessories and the exhaust system.

Your stock 302 power-steering and air-conditioning (if so equipped) brackets will not work on the 351W, but there's good news. FRPP offers a 351W Engine Swap Accessory Drive Kit for the '85-'93 Mustang that is available with the power-steering bracket only (M-8511-A351) or with both the power-steering and air-conditioning brackets (M-8511-B351).

Whatever exhaust system you currently have will work, but the headers you have (factory or otherwise) will not, again because the 351W is so much taller. MAC offers short-tube 351W swap headers (PN E358692) that will bolt up to the stock or stock configuration aftermarket H-pipe, as does FRPP (PN M-9430-A58 for '86-'93; PN M-9430 R58 for '94-'95). MAC, Hooker, Hedman, Coast High Performance, and a host of other manufacturers offer long-tube headers.

While the stock fuel system will sustain a stock 351W, odds are the 351W you have planned won't be stock--so the fuel system will likely require some modification. Beginning at the fuel tank, replace the stock pump with a larger unit, such as FRPP 150- or 190-lph pumps. The 150 is good for about 400-plus horsepower; the 190 is good for about 500 using the stock lines and 351W rails. Higher horsepower levels will likely require a custom fuel system with a larger pump, lines, and aftermarket rails.

Choosing the correct injector for the horsepower level you plan to attain is critical. A mildly built 351W can use 24-lb/hr injectors, although it's more likely you'll have to use 30- to 36-lb/hr injectors (36-lb/hr units are no longer available via FRPP). Whether you're building a more normally aspirated engine or a serious supercharged engine, you'll need a mass air meter calibrated for your new injector size, such as those offered by Pro-M and FRPP. Finally, in order to run fuel injection on a 351W, Ed Marsh says you'll have to get a distributor from an EFI 351 truck (5.8L), again because of the difference in deck height. Find one at the junkyard, or buy one new from Ford (PN E7TZ-12127-D). If you're using a later, roller-cam-equipped engine ('93-up), you'll also want to replace the cast-iron distributor gear with a steel gear.

Horsepower makes heat, so even if the 351W you plan to install is next to stock and your original radiator is in good condition, it's likely you're going to need a bigger, better radiator. Again, how much cooling you will need is directly proportional to the amount of horsepower you'll be making.

U.S. Radiator in Los Angeles, California [(323) 778-5390], is a great source for copper/brass radiators, while Fluidyne in Mooresville, North Carolina [(888) FLUIDYNE], or Griffin in Townville, South Carolina [(864) 845-5000], can set you up with the correct aluminum radiator for your application. Using a new or aftermarket water pump is also a good idea.

Rather than bore or confuse you with all the legalese involved with engine swapping, suffice it to say that swapping a 351W into your '86-'95 should be legal in California--or states adopting its emissions guidelines--provided you don't defeat or remove any of the factory emissions equipment. This includes, but is not limited to, the smog pump, the engine-control computer, the original cat H-pipe, and so on.

However, modification is always a touchy subject--even with a 302--so it's important that you carefully map out what you are considering before you do it. Then try to determine if (A) it's legal or (B) it will pass California's rigorous Inspection and Maintenance (IM) program, commonly known among enthusiasts as a "smog test."

Keep in mind that just because the part(s) you plan to install carry an E.O. (executive order) number, it doesn't necessarily mean the car will pass IM. Parts are certified independently, except in the case of certified power packages, so when various emissions-legal parts are mixed and matched, the engine may not pass. Under current guidelines, the owner of the car must do whatever it takes to make the engine pass when it has been modified, regardless of cost. In other words, don't get too carried away when you build your 351W--or any engine for that matter--because you may be forced to dispense with the big injectors, cam, and after- market computer in order to get your car to pass.

In summation, the wisest decision is to contact a referee station in your area, tell them what you have planned, and find out if it's legal. It will save you a lot of time and expense later.

Not surprisingly, the 351W weighs more than the 302--an additional 100 pounds when you're comparing apples to apples. If you're replacing your 302 with a 351W of like configuration (i.e., both have iron heads), the added weight won't adversely affect the handling of your car, and it will drop front ride height only an additional 1/4 inch, according to our experts. However, if you want to gain the muscle and lose the fat, you can use aluminum heads, a tubular K-member, an aluminum radiator, a fiberglass or carbon-fiber hood, and move the battery to the trunk (or any one of the above). These mods will make any weight difference imperceptible.

If you're considering extra cubes, then chances are you're wrestling with a fairly common dilemma: Do you build a 347 out of your 5.0 or step all the way up to a 351? Perhaps the following info will help you decide.

351W: Advantages
* Strength: The 351W block is stronger than the production 5.0 by a long shot. Thicker walls, a 3-inch main, and 2.311-inch rod journals (versus 2.248/2.123 for the 5.0) are contributing factors.

* Taller Deck: The 351W features a deck height of 9.503 inches versus the 5.0's 8.206 inches. This means a longer rod can be used for even more cubes--up to 435 with a production two-bolt block, and 454 cubes with a four-bolt FRPP block, according to George Klass at Coast High Performance.

* Rod-to-Stroke Ratio: In stock configuration, the 351 has a better rod-to-stroke ratio than a 347 (1.70:1 for the 351W versus 1.58:1 for the 347) by virtue of its longer rods (5.956 versus 5.400 for the typical 347 rod). The 351 also features 1/2-inch head bolts instead of the 302 block's 7/16-inch bolts.

351W: Disadvantages
* Size: The 351W is 2.250 inches wider than a 302, necessitating a number of changes (at additional cost) to make the swap possible. Hood clearance can become an issue, and there will be less room to service the plugs.

* Weight: As discussed in the Keep the Muscle, Lose the Fat sidebar, the 351W is beefier and is typically more than 100 pounds heavier than a 302-based engine.

347: Advantages
* 302-Based: The 347 is created when a 302 block is bored 0.030 and fitted with a 3.400-stroke crank and custom rods/pistons. This means a 347 has the extra cubes you desire, yet it can still use the same headers, manifolds, brackets, and so on as a stock 302.

* Weight: The 302-based engine is more than 100 pounds lighter than the 351 in stock form, and it can be made downright feathery with a few aluminum components.

347: Disadvantages (and perceived disadvantages)
* Limited Growth: While 347 ci is certainly a respectable number, it's the practical displacement limit for a two-bolt-main production block.

* Limited Strength: A two-bolt-main production block is typically capable of withstanding up to 600 hp, and that's with a girdle, studded mains, and so on. Even a mildly built 347 with a supercharger can bust that figure. An R302 block will solve the problem, but there goes your budget.

* Poor Rod-to-Stroke Ratio (perceived): There has been a lot of talk about the 347's rod-to-stroke (R/S) ratio. Simply stated, the R/S ratio is the length of the connecting rod (center-to-center) versus stroke of the engine. A higher ratio means the piston stays at top dead center longer, promoting better combustion and, theoretically, more power. Compared to the 351W's 1.70:1 R/S ratio, the typical 347's R/S ratio of 1.58:1 doesn't look good, but it's actually better than a lot of other noted performance engines, including the 454 big-block Chevy (1.53:1) and 400 small-block Chevy (1.48:1). Even the legendary 428 CJ was only marginally better than a 347 at 1.63:1. Unless you're building an engine to compete with Billy Glidden, R/S ratio really doesn't add up to much in an otherwise well-built engine.

* Oil Burner (perceived): Piston design is critical to the success of any 347 kit, according to George Klass at CHP. Trying to improve upon the 347's R/S ratio only moves the pin further up into the piston. If the pin is moved up into the oil ring land, the top of the pin will be located above the oil ring, allowing more oil to get past the oil rings and into the combus- tion chamber. This is how the 347 got a reputation as an oil burner. However, George says, many kits--including CHP's--place the pin below the oil ring, so oil consumption is not a problem.

Cost Factor
The next thing you'd probably like to know is, which would be cheaper, a 347 or a 351W? As discussed, the 351W requires numerous extra parts to accomplish the swap, while the 347 doesn't. However, depending on what 347 kit you purchase, the initial short-block may be more expensive than a 351W. Since we can't know what combo you have planned, the best idea is to add up the cost of a 351W, factor in the extra parts, and then compare that to the cost of the 347, keeping in mind both engines can use the same heads. Our guess is that the 347 will probably be less, but depending on how serious you plan to get, a 351W swap could be equal to, or less than, the cost of a truly serious 347.