The Smeding 347 EXTREME
The biggest performance improvement between the 302 and the 347 is the increase of 45 cubic inches to the engine. This is accomplished by installing a longer stroke crankshaft (3.4 inches) and increasing the bore size (4.030 inches). A new nodular iron crankshaft made by Scat Enterprises in Redondo Beach, California, is fitted into the main bearings of the Ford block. Whenever the crankshaft stroke is increased, the crankshaft counterweights also need to be increased in size to balance the engine correctly. Because the counterweights are larger in diameter, the stock connecting rods are not long enough to provide sufficient clearance between the piston pin boss and the crankshaft counterweight when the piston moves to the bottom of the cylinder.
 To accommodate a longer stroke...  To accommodate a longer stroke and longer connecting rods requires a special piston. The forged-aluminum pistons used in the 347 have the pin relocated up toward the top of the piston. The compression height is a mere 1.09 inches. |  The Edelbrock RPM Air Gap...  The Edelbrock RPM Air Gap 302 is a high-rise intake manifold design that will feed the engine a large amount of air. The drawback to a high-rise design is that it places the carburetor much higher on the engine. |  A 347 Extreme makes excellent...  A 347 Extreme makes excellent horsepower because of the high-flow Edelbrock Performer aluminum cylinder heads. They have 2.02-inch-diameter intake valves and 1.6-inch-diameter exhaust valves. |
The stock connecting rods are replaced with longer, high-performance connecting rods that measure 5.4 inches, center to center. These high-performance connecting rods also have stronger 3/8-inch diameter bolts and nuts. The pistons on the 347 Extreme are forged aluminum. Because of the increased crankshaft stroke and longer connecting rod, the piston for the 347 needs to be much shorter than a stock piston. The distance from the top of the piston to the center of the piston pin is called the compression height. The compression height dimension for the 347 is 1.09 inches. The 347 comes with Edelbrock Performer 5.0/5.8L aluminum heads. Large 170cc intake ports and large exhaust ports allow the 347 to breathe as well as any small-block engine. The intake valve diameter measures 2.02 inches and the exhaust valve diameter measures 1.6 inches. Rocker arm studs measure 3/8 inch in diameter and accommodate an adjustable valvetrain.
 The rotating assembly of every...  The rotating assembly of every 347 is meticulously balanced at Smeding Performance. |  The longer crankshaft stroke...  The longer crankshaft stroke and the larger connecting rod nuts require that the bottom of the bores be notched for clearance. The bores are notched with a handheld grinder. |  All of the bearings and rear...  All of the bearings and rear main seal surface are coated with assembly lube before the crankshaft is installed for the final time. |
Possibly the best performing intake manifold ever designed for the evenly spaced Ford intake ports is the Edelbrock RPM Air Gap 302, PN 7521. It sits atop the 347 Extreme and supplies large amounts of air/fuel mixture to each cylinder. The manifold has equal length and gently radiused passages, and the high-rise design only raises the carburetor mounting pad 1 inch higher than a stock 302 intake manifold.
The engine comes equipped with a hydraulic roller lifter camshaft using the stock Ford roller lifters. All '85-and-later 302 engine blocks come machined for a roller camshaft and lifters, but because of the short deck height of the 302, the roller lifters can only be installed or removed from the block without the head bolted into place. The Edelbrock heads have a groove machined into the deck that makes installation and removal of roller lifters possible without removing the heads. The aftermarket performance camshaft included with the 347 has 212/222 degrees of intake/exhaust duration at 0.050 lift and 0.489/0.510 inch of intake/exhaust valve lift. The intake and exhaust lobe centerlines have a separation angle of 112 camshaft degrees. Activating the valves are fully adjustable aluminum roller rocker arms. The rest of the engine consists of a new high-performance oil pump, timing chain and sprockets, a new balancer, all new fasteners, and Fel-Pro gaskets and seals.
 The center main bearing also...  The center main bearing also controls the crankshaft thrust. Ben Smeding lightly taps the crankshaft fore and aft to set the main bearing in place before tightening the bearing cap to the final torque setting. |  All of the 347 Extreme engines...  All of the 347 Extreme engines use a Fel-Pro one-piece rear main seal. |  The bearings are installed...  The bearings are installed into the engine block and connecting rods, and then measured with a bore gauge. The crankshaft journals are measured with a micrometer. The clearances are determined by subtracting the micrometer measurement from the bore gauge measurement. Smeding Performance pays very close attention to bearing clearances and likes to keep them on the low side of the specs. |
 After the rings are installed...  After the rings are installed on the pistons with a ring expander, the pistons are slid into the cylinders using a ring compressor. A gentle push with the handle of a hammer is all it takes. |  It is tight, but with the...  It is tight, but with the correct rods and pistons the Scat Enterprises crankshaft will fit nicely in the 302 block. |  If you decide to build a 347...  If you decide to build a 347 yourself, make sure you follow the connecting rod bolt torque specs from the rod manufacturer. They will be different than the specs provided by Ford for the stock rod bolts. |
 The 347 Extreme comes with...  The 347 Extreme comes with a high-quality double-row timing chain and sprockets. |  A brand-new timing chain cover...  A brand-new timing chain cover is included with the 347. |  To lower the compression for...  To lower the compression for 87 octane fuel, a dished piston can be installed (on left). |
 Before installing the roller...  Before installing the roller lifters, Ben Smeding visually inspects each lifter and then rolls each by hand, feeling for any roughness in the bearings. He then coats the roller surface and bearings with 30 weight engine oil. |  Aluminum heads require special...  Aluminum heads require special head bolts. They should be equipped with either a shoulder or washer under the head of the bolt to keep it from digging into the head bolt boss. The head bolts for aluminum heads are on the left. |  Coat the head bolt boss with...  Coat the head bolt boss with a small amount of moly grease before installing the bolts. |
 Aluminum roller rockers with...  Aluminum roller rockers with a 1.6:1 ratio are provided with the 347 Extreme. |  One of the nice features of...  One of the nice features of the factory roller lifters is that the alignment bars sit on the top of the lifter bores. Aftermarket roller lifters are heavier because the alignment bars must travel up and down with the lifters. The Edelbrock heads have a groove above the lifters that allow the lifters to be replaced without removing the heads. |  Here it is. It is hard to...  Here it is. It is hard to believe that this compact little engine can make so much horsepower and torque on pump gas! |