For as long as people have been racing cars, they have been building stroker motors. Stroking a short-block for additional displacement is a rather straightforward process that involves increasing the length of the crankshaft stroke and enlarging the cylinder bores. A block’s deck height, bore spacing, cylinder wall thickness, and pan rail spacing are the primary factors that determine how much an engine can be stroked. These dimensions vary for not just small- and big-blocks, but also for aftermarket blocks when compared to stock units.
After applying sealant around...
After applying sealant around the perimeter of the freeze plugs, the easiest way to install them is with a socket and hammer. Smeding uses a socket that’s slightly smaller than the lip of the freeze plug and taps it into place.
For a standard 4.000-inch bore 350 block, stroking it out to 383 ci is incredibly popular. That’s because they can easily handle an extra 0.030 inch of bore, and increasing the stroke from 3.480 to 3.750 inches requires minimal block clearancing. Increasing the stroke even farther to 3.8750 or 4.000 inches is possible—for displacement totals of 396 and 408 ci, respectively—but it creates far more clearance issues among the rods, block, and camshaft.
On the big-block front, the ubiquitous 454 Rat motor—with its 4.250-inch bore and 4.000-inch stroke—can net an easy 42 extra cubes with a 0.060-inch overbore and a 4.250-inch stroker crank. This yields a total of 496 ci, which may be old-school by today’s standards, but it’s still a very capable combination. Stepping up from a production 454 block to either a GMPP 502 block, or an aftermarket unit with thicker cylinder walls, allows opening up the bore to 4.500 inches for a total of 540 cubes.
To keep things simple, we’ve focused mainly on production GM blocks, but suffice it to say that aftermarket blocks are entirely different beasts. With thicker cylinder walls, taller deck heights, raised camshaft tunnels, and oil pan rails that are spread way out, they can accommodate truly absurd displacement figures. These days it’s possible to build a 454ci small-block Chevy, and Rat motors that pack 665 ci. As no surprise, the biggest drawback of aftermarket blocks is price. While second-hand production blocks can be had for less than $200, aftermarket units can be a bit more.
The excitement and rush to...
The excitement and rush to put a short-block together can make it easy to overlook the little things. Both Gen I small- and big-blocks have coolant drains along the sides of the block, and oil ports near the filter boss. They must be closed off with pipe plugs to prevent a big ugly leak.
When it comes down to it, what’s actually doing the stroking in a stroker motor is the rotating assembly, which consists of the crankshaft, connecting rods, and pistons. Options abound when selecting a rotating assembly, and the first decision that needs to be made is the target displacement of your engine build, as this will determine crankshaft stroke and piston diameter. Once those critical dimensions have been established, it’s time to decide whether to opt for forged hardware, or stick with less expensive cast parts. This decision comes down to the intended use of the motor, and the builder’s budget.
Today’s cast-steel crankshafts are remarkably robust, capable of handling 500-plus horsepower in small-blocks, and more than 750 hp in big-blocks. Most manufacturers recommended forged steel cranks in applications that exceed those horsepower figures. An added bonus is that the lower grades of steel, such as 5140 and 4130, that were popular just a decade ago have been almost entirely replaced by the popular 4340 steel alloy. These forgings will take as much power as most people can reasonably throw at them. Price-wise, cast cranks can be had for as little as $200-$300, while forgings cost more than twice as much.
During the balancing process,...
During the balancing process, bob weights are bolted to the crankshaft. They’re equal in mass to 100 percent of the rotating weight (big rod ends, rod bearings), and 50 percent of the reciprocating weight (pistons, pins, locks, small rod ends). With today’s lightweight rods and pistons, material is typically removed from the crank counterweights, although heavy metal is sometimes added in extremely long-stroke cranks that have small counterweights. Since a crankshaft acts as a lever, the farther away from the crank centerline the weight is removed, the greater affect it has on balance.
Moving up the assembly to the connecting rods, just about any aftermarket unit you purchase today will be a forged steel piece, with 4340 the most prevalent alloy. A mere $250 gets you a brand-new set of I-beam forgings from companies like Scat and Eagle, which will handle roughly 500 hp in small-block applications and 700-plus in big-blocks. Most manufacturers that source their rods from overseas offer H-beam rods as an upgrade to their entry-level I-beams. For $500-$600, they can endure loads well in excess of 1,000 hp, making them perfect for big-horsepower power adder combos. That’s not to say H-beams are superior in design to I-beams, since companies like Oliver, Crower, and Lunati offer domestically produced I-beams that have long been held as the gold standard of durability.
After the crank has been balanced,...
After the crank has been balanced, Smeding polishes all of the main and rod journals. This removes all surface scratches prior to assembly.
With the machine work complete,...
With the machine work complete, it’s time to start assembling the short-block. The main bearings have tabs that help locate them into a slot in the block. The block half of the bearing has an oiling hole, while the main cap side does not.
Once the main bearings have...
Once the main bearings have been installed, the main caps must be torqued down before checking bearing clearance. Using a dial bore gauge to measure the bearing inside diameter, then comparing it to the diameter of the main journals measured with a micrometer will give a good indication of the bearing clearance. As long as a block is in good shape, or has been align-honed, variations from cap to cap should be minimal, and can be adjusted if necessary with undersized bearings. For street engines, 0.0025- to 0.0035-inch clearance is typical, while race motors may have 0.0035 to 0.0040 inch of clearance.