1972 350 Chevrolet Pickup Engine - Tech - Build Your First Engine

The pen contrasts the compact skirts featured on the forged pistons that come with the Powerhouse 383 kit. Their flat-tops will deliver approximately 10:1 compression with a 64cc chamber volume on our 0.030-over motor. Each piston-and-rod assembly weighs 56 grams less than the stock rod and cast piston it replaces.

The kit features external balancing, as indicated by the brand-new 400-style scalloped harmonic damper and weighted 168-tooth flexplate. External balancing is commonly used in situations where conventional internal balancing isn't possible because the od of the crankshaft counterweights is limited by the physical dimensions of the block, or by interference problems with the pistons and cam. External balancing is also needed when the crankshaft counterweights do not have sufficient mass to offset the mass of the reciprocating and rotating components to achieve needed balance. This is a classic scenario in engines equipped with cast crankshafts like our 383, which are typically about 20 percent lighter than forged crankshafts.

Because the Powerhouse 383 kit is prebalanced, we skipped the balancing rig and saved another $150. But remember, if you're not working with a prebalanced kit and you make any significant changes to your combination, balancing is essential. A single ounce of metal (28 grams) has a dynamic weight of over 700 pounds when it's placed on a spinning crankshaft counterweight.

With our choice made to install an all-new rotating assembly, we turned our attention to preparing the block. Each deck was given a light 0.006-inch cut (two 0.003-inch passes) on the JMS Block Master 85-B to restore flatness for gasket sealing. Remember, aggressive material removal (0.020 or more) will decrease total the deck-height measurement and can affect compression ratio, piston-to-valve clearance with high lift, high-overlap cams, hydraulic lifter preload, and intake manifold alignment. Less is more when it comes to decking; thinner decks are less rigid.

Corvette and musclecar restorers beware! If your block is a rarity, know that it doesn't take much to eliminate the critical engine code stampings found at the front of the passenger-side deck. The stampings on our dirt-common 350 block were 80-percent gone after a mere 0.006 cut! If this was an original DZ or MO 302 Z/28 block, we'd have just lost a big chunk of the car's value! If you're in doubt, either skip the decking (if it's not deemed essential) or ask your machinist not to disturb the stamped pad.

Adding a stroker crank to any block requires close attention to ensure safe clearance, as the rods describe a larger circle when the crank spins. With many years experience building stroker motors of all types, JMS has devised a "road map" that directs a series of crankcase clearance cuts to ensure the 383's 3.750-inch stroke (0.270 inch greater than the stock 3.480-inch stroke) doesn't make the rods go "clunk" with the bottoms of the bores. The work is done on the JMS Do-All vertical mill using a 1-inch rotary cutter. The resulting clearance notches average 0.020 deep.

With the main caps installed and torqued to 70 ft-lb, the No. 2, 3, and 4 main bore diameters measured 0.0005 under the acceptable minimum spec. A tight bore can reduce the oil clearance and lead to premature main-bearing wear or outright failure. So Sal Alcarez loaded the block onto the Sunnen CH100K line-hone machine and corrected the issue. After three light passes, all five main bores measured 2.6410 inches on the nose. The acceptable range is 2.6406-2.6416 inches.

A 151/48-inch-thick torque plate was installed on the deck and torqued to 70 ft-lb during the cylinder-honing operation on the JMS Sunnen CV-616 Cylinder King. The plate simulates the presence of the installed head for accurate as-run bore conditions during honing. This enhances ring seal as well as prolongs piston, bore, and ring life.

The Powerhouse 383 kit uses press-fit piston pins. To eliminate the often brutal process of using a hydraulic press to fit the pins, JMS uses a Sunnen CRH-50 rod heater to warm and expand the small end. The pins slip right in place before the rod cools down. Floating pins offer no real advantage other than easier assembly and disassembly.