302 to 351W Swap

Why swap a 351W
What kind of power can I expect?
What parts do I need?
What about fitment issues?
What is the cost of swapping my 5.0 for a 351W?

Why swap a 351W

Swapping a 351W in place of your 5.0 is a somewhat budget-friendly way to make a lot of power, and to subsequently go very fast. A 302 (5.0L) based engine is not incapable of making good horsepower, but it certainly has many more limits than a 351W motor. Why? Well, first off, the displacement issue. Whoever coined the phrase 'there is no replacement for displacement' is, frankly, a genius. A 351W engine has an extra 49 cubic inches over a stock 302 cu motor. That is an advantage right there. If you recall, an engine is basically a large pump. A larger pump can move more air, and thereby is more powerful.

Secondly, a 351W has a ton of room to grow. A 302-based motor can be stroked all the way to 347 cu, which is only 4 cu difference from a 351. So why not just stroke the stock 302? Well, you could certainly do that, and you'll get excellent results. However, Ford production 302-based blocks are weaker. Production 302 blocks are not as thick, and can only be stroked to a maximum of 347 cu for this reason. And because they are weaker, 5.0L blocks have a lower horsepower limit before cracking (for the record, it is shown to be around ~500HP). On the other hand, 351W blocks have thicker webbings, and also beefier main and rod journals, making it overall a much stronger block and crankshaft. The aftermarket world has shown that Ford-production 351W blocks are good up to 750HP. So we start with a block that is 351 cubic inches, and can hold up to 750HP. Want to go bigger? Not a problem. You can stroke a 351W all the way up to 427 cubic inches - creating a behomoth with such grand power it could easily reverse the rotation of the earth!

Finally, there is the aspect of cost. In the first paragraph, the term 'budget-friendly' was thrown out there. A 351W swap is a budget-friendly avenue because of the availability of parts, and the surprising minimal amount of work needed to slip one into a Fox or SN95. No need to buy an expensive aftermarket block, just head to your local scrapyard. Furthermore, 351Ws utilize the same bellhousing pattern as a 302, so any transmission that will bolt up to a 302 engine will also mount to the bigger Windsor, no modification necessary.

Reasons for 351W swap (summarized):

  1. No replacement for displacement
  2. Stronger block (~750HP)
  3. Affordability and availability of parts (i.e: scrapyard)
  4. No fabrication work necessary
  5. Same bellhousing pattern as a 302

What kind of power can I expect from a 351W swap?

In truth, there is no guaranteed answer regarding this question. All I can provide is some guidelines and approximate estimates, based on other enthusiasts real world results. To make decent power with a 351W, it is assumed you will spend a little money to dress it up, not just drop in a 351W straight out of a truck. If you do the latter (drop in a stock 351W from an F150 or the likes), prepare yourself for disappointment. In stock truck trim, a 351W will be slower than your stock 302 powered Mustang. Why? Well, it is engineered for a truck, not a sports car. How do we change this? Easy, heads, cam and intake swap!

A mild 351W build will easily surpass 350HP. Throw on some good aftermarket heads with intake, and a cam to tie them together, and 500HP+ can be had out of these engines. It really depends on how deep your pockets are (as is the case with most things). To hazard a guess, I would say the average 351W falls around ~450HP mark, with plenty of room to grow as more cash becomes availabile later down the road. If you're throwing a 351W into your Fox or SN95, be prepared to leave tire marks, and potentially, skid marks. These engines, when done up, are wicked fun!

What parts do I need to complete the 351W swap?

The 351W swap is what we like to call an 'almost direct-fit swap'. Sounds like a typical marketing gimmick to me... Truth be told, it isn't too difficult to swap. Most of the 302 parts swap over, but there are some that do need to be changed. All the major stuff will drop right in, no modification to the engine bay or k-member needed. What parts do need to be swapped? Let's dive in.

  1. Oil pan
    The stock 351W oil pan is a front-sump, whereas the 302 uses a rear-sump. Thus, the 351W oil pan needs to be changed to a rear-sump (like the 302) in order to fit in your Mustang (otherwise it will not clear k-member). Ford Racing has a good 5-quart kit available, or there are larger offerings from Canton or Moroso, in the order of 7-quarts and with the option of a wind-age tray.
  2. Oil pump, shaft, pickup
    A new oil pump and shaft is cheap insurance, whereas a new pickup will be necessary (remember, we went from front-sump to rear-sump), the original 351W pickup will not work.
  3. Flywheel and harmonic damper
    Ford's 351W uses a 28oz imbalance versus a 302's 50oz imbalance, thus meaning you will need both a new flywheel and harmonic damper. In this case, you're looking for a 157-tooth 28 oz flywheel to use with a 10.5" clutch . Also, the flywheel bolt pattern differs. An alternate option is to have a machine shop trim the 50 oz imbalance down to 28 oz and re-drill the mounting holes in the correct locations.
  4. Distributor
    The distributor too needs to be changed, as the 351W has a larger oil pump drive shaft as well being physically taller. Grab a dizzy from any EFI 351W (5.8L) truck out of a scrapyard, or any aftermarket vendor will be more than willing to sell you a brand new one as well. It should also be mentioned, if you are using a roller cam, swap the stock cast-iron distributor gear for one of steel.
  5. Exhaust manifold/headers
    Fox style headers, be it short or long tube, will not work due to clearance issues. Instead, you must seek a set of headers labeled as '351W swap headers'. It is easier (and cheaper) to get shorty headers, but I believe there are some long-tube conversions out there as well. Check out companies like Ford Racing, Kooks, Hooker, BBK etc. There are even sets available on eBay, however I cannot attest to their quality (but check out their feedback, it could be worth it).
  6. Intake manifold
    A 351W has a greater deck height and separation, thus rendering any 302 lower intake useless. It simply will not bolt up because they are not physically wide enough to bridge the gap. Rather, you will need to find a specific 351W lower intake. However, this isn't really a problem as all major aftermarket companies offer them (Ford Racing, Edelbrock, Trickflow, Holley etc). On a side note, 302 heads will work without any issues, just the bolt-holes will need to be enlarged to fit 1/2" fasteners.
  7. Accessory brackets & crank spacer
    The last items that are not a direct swap are accessory brackets, namely the power steering and AC bracket. Depending on what accessories you are running, some of the 302 brackets will not fit. Ford Racing sells a replacement kit with the right geometry for around $60-$70, as does March. Furthermore, a crank spacer may also be necessary to help align your accessories and serpentine belt. Some guys are able to make it worth with just the regular 5.0L parts, whereas others can't. As mentioned, it depends on what accessories you wish to run, and where you want to place them.

The above parts are what is needed to get a 351W to both fit and run inside of your Fox or SN95 Mustang. However, there are still a ton of other factors that need to be addressed, but are not directly involved with the swap. For instance, if you plan on making more power (which is the whole idea of using a 351), you'll need a fuel system to match. Larger injectors or carb, more powerful fuel pump, throttlebody etc.

Will a 351W fit in my engine bay?

It depends. As mentioned, a 351W is a direct, drop-in engine in terms of mounting location. It will bolt up to the stock motor mounts and will fit in the engine bay width wise without issue. However, seeing as a 351W has a bigger deck height and is thus a taller engine, depending on what intake manifold is being used, there could be some clearance issues under the hood. There are two ways to fix this. You could either purchase a hood with a larger cowl, or you could change the motor mounts to drop the engine a bit farther down (or do both). Recommended motor mounts are the OE units from any 87-93 convertible Mustang. They are stronger than regular mounts, and will better deal with the added weight of the engine (5.8L is heaver than the 5.0L). There are also aftermarket solid motor mounts out there that will drop the engine by 3/4". (HP Motorsports comes to mind for this, but I'm sure there are other companies as well.)

What will a 351W cost me?

Cost is another highly subjective question, as not only is it region dependent (i.e: scrapyard prices), but owner dependent as well. If you have a whole top end laying in the garage and only need a 351W shortblock, then it is a pretty cheap build. If you are starting with nothing, then expect to spend a pretty penny as you will need a better top end than what is stock if you wish to make any power. For this reason, when I list my 351W swap estimate in a few moments, it is a quote for only 351W necessary parts. It is assumed you have the supporting mods already covered (top end, fuel needs, labor costs, bits & bobs). Here goes:

351W engine$400Scrap yard
Oil pan $1355 qt, new, w/pickup, dipstick, tube
Oil pump & driveshaft $75New
Flywheel & balancer $150-$200New
Distributor $30 Scrapyard
351W headers $120-550 eBay - Summit
Accessory brackets $70New

Again, please keep in mind these are only estimated costs, and do not include other things that could be necessary such as machine work, install labor, gaskets etc. It by no means is a comprehensive monetary value, but rather a rough estimate of what it would cost to accumulate the parts needed for a basic 351W swap. If you want to make 500HP, you'll need some nice aluminum cylinder heads, which of course are not factored. Furthermore, not all 351W blocks are roller blocks - early blocks were flat-tappet. There could also be the cost of getting correct lifters and what not to convert a flat tappet to roller if that is the route you wish to go.