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
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.
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
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
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
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.
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
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
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.
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.
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.
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.
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.
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.
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.
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
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