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Articles

How To Build A
Budget 347
Stroker Motor

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Article courtesy of
5.0 Mustang & Super
Fords
, July 2006

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Tech Articles
 
Half-Price Hardware: How To Build A Budget 347 Stroker Motor
How to build a fun-time 347 for about half the price of an all-out race engine

Budget Stroker Engine Build
Severo Diaz, known as "Pinto" around the shop, gives the budget 347 engine a final couple of checks. While not a low-buck engine, this 347 takes a stand in the reasonable dollar range while still reaching for 500 rowdy horsepower.

Horse Sense: The newest part on this budget engine is the Funnel Web intake manifold from the Parker Company. Probe/Coast hasn't run this intake, nor have we, so it'll be fun to see how it does on the dyno next month.

Some magazines make a living screaming headlines about Junkyard Warriors--we're not one of them. Like everyone else who's been once around the high-performance block, we realize there is no such thing as pocket-change racing or even sterling street performance. Speed costs money, and that's that.

The trick to real-world budget performance is learning what you can live without while getting your speed fix. For example, the goal here is to build 500 hp from a small-block Ford and not go totally broke in the process. By not going broke, we have to swallow once, take a deep breath, and admit it still takes $7,733.06 to build a turnkey 500hp engine, and for that we aren't going to get everything. We'll have to give up the last word in durability--no bulletproof aftermarket blocks--and there is little budget for extensive hand-porting or expensive systems. Such an engine will have to be built from off-the-shelf pieces, and nothing exotic at that. And while six or seven grand is still a pile of money, it's a long way from the $13,000 to $14,000 it takes to assemble a full-on forged and Dart-blocked race engine these days.


Probe and CHP

Don't worry if you're a bit confused by the relationship between Probe Industries and Coast High Performance. The two companies are closely aligned and share much of the same physical plant, but Probe is the manufacturing company and Coast is the sales side of the organization. So, if you want to purchase an engine, call Coast High Performance and buy one of theirs, and understand it will have Probe pistons inside it. Got it?


Budget Stroker Engine Build
Probe uses a variety of crankshafts in its engines, but we most often see Scat cranks when visiting Probe. Our budget 347 was no exception--it uses this 3.400-inch-stroke Scat cast-steel crank. Cast in China and machined in the United States, the Scat crank is a bit heavy and features now-standard counterweighing and profiling practices; it is quite stout and should prove durable. It's the centerpiece of the 347 stroke job.

For our purposes we'll run the engine carbureted on the dyno to see how close we came to our power goal. Carburetion is less expensive than fuel injection, unless, of course, you already have a tunable fuel-injection system you can modify to work at high rpm. That means a possible slight loss of driveability, definitely less fuel economy, and no hope on the emissions front.

All these parameters lead us to what the typical bracket racer would recognize as a good budget build. The first step to power is displacement--there is no replacement for displacement--and the best bang for the cubic-inch buck is, of course, a 347.

The next step is to pack as much air as practical into the cylinders, meaning a high-flow cylinder head and a really big cam, then squeezing it hard via elevated cylinder pressure to get some work out of it. To date, a turbocharger is the most efficient way to squeeze air, but that--and all other forms of supercharging--is off (budget) limits. Instead, we'll do it the old-fashioned way, with a generous dollop of compression.

Budget Stroker Engine Build
Called Machine Beam Rods by Probe, these are good budget connecting rods. Forged and fitted with ARP hardware, they are a smart choice for a powered-up, but not overpowered or screaming-rpm engine.

What we've spec'd out is a 347 stroker packing a big, mechanical camshaft, decent heads, and a free-flowing intake manifold and carburetor combination. That's just the sort of thing Probe is used to putting together for its bracket customers, and we followed along as they demonstrated how they would put together a budget 347. This month we're showing the parts and highlights of how they went together; next month we'll strap the engine to one of Westech's dynos to see how the power comes out.

A final word on trading dollars for performance: This engine should party hearty, but it will feature a choppy idle, thirst for premium gasoline at the least, won't last 100,000 miles--and don't even think about emissions. But it will scoot, and for a Saturday-night shaker, bracket or other fun machine, it should provide a grin made all the larger because all that speed didn't cost so much.

Probe saves some money on its machined beam rods by not finishing the surface of the beam's "bowl," which leaves this rough surface. If that bothers you--it shouldn't on the majority of fun-car engines--Probe has plenty of other, more finely finished rod options.
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Probe is famous for its pistons, and for our budget bracket motor the company reached for the SRS forged line with a big 9cc pop-up to raise the compression ratio. This dome shape works with all inline valve heads, save the Twisted Wedge and Edelbrock Victor castings with their canted valves.
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The standard piston pins with a 0.150-inch wall thickness were used, and they're plenty strong enough for 500 hp in a budget engine. They're packaged in the SRS piston line, and they're made from 1018 material and are hard chromed. Probe offers tool-steel pin upgrades in various thicknesses.
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Rings and bearings used in Probe's budget build are its standard Perfect Circle and Clevite fare. The ring package is the now rather standard 1/16, 1/16, 3mm sizing. With the piston pin in the oil ring groove, an oil-rail support is included with the piston. It supports the oil ring and keeps it from rotating in its groove and thus working its ends out of the groove. According to Probe, the oil-ring groove climbing was an issue years ago, but today's heavier rings don't have that problem, which makes the oil-rail support a belt-and-suspenders approach.
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For a budget build such as this, Probe uses an Elgin EM-68HV oil pump. It's packaged with gaskets and a standard oil-pump driveshaft, which Probe replaces with its in-house-built heavy-duty driveshaft. Beefy oil-pump drives are--and should be--a staple of all but the lowest lo-po small-block engine builds.
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Low budget or not, having more oil on hand and keeping it away from the rotating assembly is important to any performance engine build. Probe fitted this engine with a basic Canton deep-sump pan. There's nothing fancy here--just a deep sump with no scraper or windage tray, and no trapdoors or other flow controllers. Fel-Pro pan gaskets are used to ensure sealing, and Canton supplies an oil-pump pickup and dipstick to match the deep-sump pan. Probe makes a windage tray that'll work with this combination, but it wasn't fitted to this engine.
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Probe builds its small Fords with a new replacement front timing-chain cover. It's a universal fit item with a dipstick hole and is supplied with a small 3/8-inch welch plug (think "tiny freeze plug") to seal the dipstick hole if a block- or a pan-mounted dipstick is used.
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Because it is designed to work with either early or late Ford engines, Probe's replacement timing cover features a fuel-pump mounting boss. It isn't needed for fuel-injected applications, of course, and may or may not be used in carbureted cars depending on the fuel pump used. In such cases, a simple block-off plate is fitted.
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Professional Products is a low-cost engine-parts supplier based in the United States, but the company sells parts that are almost exclusively sourced from overseas. With its extensive line of budget parts, the company figured prominently in Probe's dressing of this engine, including this elastomer-style harmonic damper. An SFI-approved unit, this damper is normally what Probe fits to its complete engines.
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Iskenderian ground the budget 347's mechanical flat-tappet cam and supplied a set of its matching lifters with EDM oiling holes in the bottom to flood the cam lobes with lube. The cam measures a healthy 263/272 duration at 0.050-inch lift, along with 0.592/0.608-inch valve lift, and a valve lash of 0.016/0.018-inch. Designed for carbureted duty, the lobe center is 110 degrees. We're expecting a choppy idle and a 7,500 to 7,800 top end from all this.
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McCord used to make this graphite head gasket, which Probe believes is forgiving and totally leak-free. Probe bought the final 5,000-gasket supply from McCord, so the company will use them for a while. When they run out, Probe will source a similar gasket, even if it has to be custom made.

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