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How To Increase Horsepower - You Can Build It!


Stephen Kim Feb 23, 2012 0 Comment(s)
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Keeping it Practical


More Cubes, Please

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.

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.

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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.

Rotating Assembly

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.

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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.

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.

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With the crank and rods sorted, all that’s left to round out the rotating assembly are the pistons. Hypereutectic pistons work extremely well in naturally aspirated applications, and feature very low expansion rates when subjected to heat. This allows for tighter piston-to-wall clearance and reduces piston slap. For nitrous and forced-induction applications, or even high-compression naturally aspirated motors, forged pistons go a long way in enhancing durability. While hypereutectic pistons are much more brittle than forgings, and tend to crack in the face of extreme cylinder pressure or detonation, forged slugs are much more forgiving. Hypereutectic pistons can be had for as little as $200, while forgings run $500 or more.

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It’s important to keep in mind that there is a right and wrong way to prioritize parts selection within the rotating assembly. Since the pistons bear the brunt of the abuse inside an engine, and are therefore the most likely components of the rotating assembly to fail, it’s not practical to spend big bucks on a forged crank and rods only to top everything off with hypereutectic pistons. A more effective allocation of any budget would be investing in high-quality forged pistons and rods, and matching them up with a cast crankshaft. Of course, if you can afford it, an all-forged rotating assembly is the ultimate in durability.


Everyone dreads machine work because even the most hard-core do-it-yourselfers can’t afford to have a boring bar or honing machine in their garage. That means you have to pay someone else to do it for you, and hope that it comes out right. While there’s no surefire way to ensure quality machine work outside of hiring a shop with the best reputation in your neck of the woods, knowing what each process entails goes a long way in stretching your budget.

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At a minimum, most engine blocks will require, boring, honing, and deck resurfacing. Depending on how badly the main caps are worn, a block may also need to be align-bored and honed. Furthermore, rusty or excessively greasy blocks can benefit from hot tank cleaning, and all rotating assemblies must be balanced prior to installation. Rates vary widely from shop to shop, but it’s not uncommon to shell out over $1,000 for these services.

Granted, quality machine work costs money, but the procedures themselves are easy to understand. Boring is typically performed on a machine like the Rottler FA, which has several cutters that rotate around a boring bar. As the bar moves down the bore, it slowly removes material until the machinist stops it when it’s within a few thousandths of an inch of the final overbore size. From there, the block is honed on machines like the Sunnen CK-10, which not just smooths out the bore surface, but also machines superfine peaks and valleys into the bore surface. Quality honing is essential for proper oil control and ring seal. Generally, race motors use a superslick finish to reduce friction at the expense of oil consumption, while street motors prefer a rougher surface for superior oil control. The align-boring and honing process is similar to boring and honing the cylinder bores, but instead it’s performed on the main caps.

Decking involves resurfacing the deck of the block with a cutting head on a machine like the Sunnen HBS-2100. Decking provides a smooth surface for the head gaskets to seal upon. It also reduces the deck height to tighten up quench clearance for improved horsepower and detonation resistance. With all the block machining complete, the last step is balancing the rotating assembly. The goal is to make sure that the rotating mass and reciprocating mass are equal, which usually requires removing material from the crank counterweights. It may seem like a frivolous expense, but balancing is not optional. A properly balanced rotating assembly is essential in enhancing bearing life and ensuring smoothing performance.

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Popular Displacement Combos

Displacement Bore Stroke Deck Height
350 4.000 3.480 9.000
383 4.030 3.750 9.000
396 4.030 3.875 9.000
406 4.155 3.750 9.000
408 4.030 4.000 9.000
427 4.125 4.000 9.000
434 4.155 4.000 9.000
454 4.250 4.000 9.000
454 4.250 4.000 9.800
496 4.310 4.250 9.800
502 4.468 4.000 9.800
540 4.500 4.250 9.800
565 4.600 4.250 9.800
598 4.600 4.500 10.200
632 4.600 4.750 10.200
665 4.600 5.000 10.700

Step By Step

With the hard work out of the way, bolting the Edelbrock Victor Jr. intake and Quick Fuel Technology 950-cfm carb is cake. Smeding rates this beastly 572 at 690 hp and 700 lb-ft of torque. Complete with a three-year, unlimited-mile warranty, it costs a very reasonable $13,000. CHP


Air Flow Research
Valencia, CA 91355
Comp Cams
Memphis, TN 38118
Quick Fuel Technology
Bowling Green, KY 42101
Dart Machinery
Troy, MI 48084
Smeding Performance
Boerne, TX 78006




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