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The quest for additional power is insatiable for many Mustang enthusiasts. If a 150 hp shot of nitrous is good, then 200 hp is even better. If 10 psi of boost feels good, then 14 psi should feel even better. If a 302 makes 1.5 hp per cubic inch, imagine what it'll do with a 351W, but why stop at 351, why not 383, or even 427 cubic inches.

351W conversions are becoming increasingly popular. With the widespread stroker kits available for 302's, attention is now being focused on stroking the formidable 351W.

There are several benefits to stroking a 351W over a 302, the most important is block strength. The factory 302 block is inherently weak and doesn't hold up well to serious levels of power and torque. The 351W on the other hand features a much beefier block design and is more suited to high levels of power and more demanding environments.

So now you've made the decision to put a stroked 351W in your Mustang (or any other Ford vehicle), what are the other considerations? How many cubes, what year block, which rods, how revable will it be? This article addresses general engine considerations, not what oil pan or dress bracketry is needed.

We've all heard the quote "There's no replacement for displacement", so let's build our stroker as big as possible, there are kits that can take a 351W all the way to 454 cid, and bigger is better right? As with everything else, bigger is not necessarily better. There are several considerations to make when engineering the displacement of a 351W stroker, rod ratio, cylinder heads and rpm limits are just a few.

The easiest and most popular stroker combination is offset grinding a stock 351W crank to 3.7" stroke, with a .030 over bore you've got 377 cid and with a .060 overbore you're at 383 cid. Eagle makes a high quality, affordable steel rod that works very well in this application. It is 6.200" long and features Chevy small block journals. Using this rod gives a very favorable 1.68 rod ratio and is just as happy revving to 6000 rpm in a mild street engine as it is at 8500 rpm in a 15:1 race engine. The rods clear the block with room to spare and no exotic crankshaft balancing is necessary.

Other popular kits offer cubic inch combinations at 408, 414, 427 and even 454. Most of these kits start with a 400M crank that is extensively modified to fit the Windsor block and feature a 4.00" to 4.25" stroke. While more cubes may sound appealing, it isn't for some applications. The primary problem is cylinder head efficiency at higher rpm's. Most small block cylinder heads were designed to be used on a 289 through 351, they weren't designed for the near big block cubic inches of a large stroked Windsor. Most don't have the port volume necessary to efficiently feed engines larger than 400 cid. So in a maximum power effort, the returns from the added cubes fall into the category of diminishing returns. Street engines are less sensitive to the high rpm airflow needs and can offer plenty of low end torque with one of the bigger strokers. Revability with 4.00" or more stroke is also a concern, the lower rod ratios and subsequent rod angles can cause excessive piston skirt wear and slapping when cold that can sometimes sound severe.

Both offset ground 351W cranks and modified 400M cranks are very durable and can safely handle 700+ horsepower. Steel cranks aren't necessary until power levels exceed 750 or you want the insurance of an indestructible bottom end.

Cylinder heads, an important consideration but one that we'll be brief with. The additional cubes need not only a head that is well designed, but also one that has relatively large port volumes so that the engine can breath at higher rpm's. GT-40 or similar heads on a stroked Windsor will provide lots of low end torque but will choke the engine off above 4500 rpm. TFS Twisted Wedge provide excellent low end and mid-range, but don't have the necessary port volumes for rpms above 6500. The old style TFS "Street Heat" or the new TFS Twisted Wedge "R" heads, the new heads from Canfield are all good choices for anyone looking to build a stroked Windsor that can pull to 7000 rpm and above. For a maximum effort, high revving (8500+), 400+ cubed Windsor, SVO's Yates cylinder heads are the only choice that will allow the engine to breath freely.

We've made the blanket statement that 351W blocks are stronger and more durable than 302 blocks, but is there a difference in 351W blocks? Yes, there is a big difference. `74 and earlier castings are noticeably beefier than the `75 to present castings, especially in the critical main-webbing area. The difference between a `74 and `75 casting is an astounding 10 lbs. of additional iron. In a maximum effort (600 hp or more) a 4-bolt main conversion is not an option, it's a necessity and only the `74 and earlier blocks have enough meat in the main-webbing to perform this machining. But there is nothing wrong with the `75 - late model castings. We've reliably run 550+ hp through them without problems. Rpm is an important consideration with the weaker main-webbed blocks and we've noted substantial main cap movement above 7000 rpm without a 4-bolt main conversion. While a stock block can be built to be reliable, if you're planning a serious effort with high horsepower and high rpm's, it's time to look at an SVO block. SVO's 4-bolt 351W block can safely handle 1300+ horsepower and is the end-all to durability concerns.

There has been much talk as to how much rpm the large journals of a 351W can endure. Some people say that bearing failure is inevitable above 6500 rpm and others say it is even lower. We've found that as long as there is adequate oil pressure and volume, the 351W is happy spinning at rpms as high as 8500. The main journals are larger than most small blocks, but they're smaller than many big blocks, and it's not uncommon to see 500 cubic inchers spinning to 8000+ rpm. Don't be afraid of buzzing your stroked Windsor as long as your oiling system and valve train is up to the task. Circle track racers routinely see 8500 rpm with their 351W's.

You've decided how many cubes you want, which cylinder heads and what year block to use, so what about the rods? With the affordable selection of aftermarket steel rods form manufacturers like Eagle, there is no reason to use modified factory rods. The modified factory rods cost nearly the same but can't offer the strength of a good steel rod. Insist that your kit uses a high quality rod, the hundred or so dollars you'll save now may cost a lot more when a rod breaks and takes the rest of the shortblock with it. Aluminum rods are also an option offered with many kits. They're not a good choice for a vehicle that sees a substantial amount of street driving. After time they weaken and can break without warning. The power advantage over heavier steel rods is marginal and in our opinion not worth the risk. Most aluminum rod manufacturers recommend checking the rods every 60 or so passes, not a practical procedure for a daily driver.

So bottom line; A 351W stroker can be very reliable and offer more power than most 302 owners can dream of. They're no more expensive than building a 302 stroker, and in high hp cases, less expensive. There are several good cylinder heads up to the task of a high torque street engine or a high horsepower race engine. All the parts necessary are readily available and usually economical. Unfortunately, some of the mail order kits we've seen are low quality and often improperly machined. As with any custom machining, make sure you use a reputable source who has plenty of experience with your stroker kit. If everything is assembled properly and the combination is matched, you'll have a formidable power plant, and we didn't even get into what happens when you use a power-adder with that stroked 351W.


SOURCE

10 Tips for Building for your first 351W Stroker

351W Stroker Kit Options - Mustang Monthly Magazine

408-Inch Ford Stroker
Serious Big-Block Power In A Small-Block Package