Back in the stone age of building stroker motors, which was only about 15 years ago, hot rodders had to settle for miniscule displacement gains through primitive means, such as offset grinding production crankshafts. Fortunately, that’s no longer the case. Due to the rise of affordable aftermarket stroker crankshafts in the past decade, cubic inches are cheaper than ever, and installing a long-arm crank is the easiest way to increase displacement. As our hobby frolics in a golden age of horsepower, no single engine component, save for the cylinder head, has advanced the cause as much as the modern crankshaft.
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Simply increasing the stroke of a standard 3.900-inch-bore LS1 from 3.622 inches to 4.000 inches adds 36 ci to the displacement tally. So unless your sanctioning body forbids it, you’re probably in the market for a new stroker crank if you’re building a motor. However, the choices are many, and not all cranks are created equally, which raises many questions. Should you settle for a cast steel piece, or step up to a forging? What’s the difference between 5140, 4130, and 4340 steel alloys? Does billet live up to its mystique? And, most importantly, what’s the right crankshaft for your application? Fortunately, this chapter helps sort everything out.
Small increases in stroke yield large increases in displacement, which is why a long-arm crankshaft is at the heart of every biginch engine combo. The overwhelming volume of affordable stroker crankshafts on the market is what has forced the rest of the aftermarket to develop blocks and cylinder heads that can keep pace.
Stroking for Displacement
In essence, stroking an engine for additional displacement involves taking advantage of extra space inside the cylinders and crankcase. Because this moves the pistons farther up and down the bores, there is a practical limit to how much stroke can be increased before clearance issues arise. As the stroke of a crankshaft is increased, the distance between the crank centerline and connecting rod journals increases. This pushes the crankshaft counterweights farther outward, reducing the clearance between the counterweights and the oil pan rails. Additionally, longer strokes increase the angularity of the connecting rods as they swing from side to side in the block, causing them to come closer to the bottom of the cylinder sleeves and the crankcase. Another area to look out for is rod-to-camshaft clearance, as longer strokes push the connecting rods closer to the camshaft as the pistons near TDC.
Fortunately, none of these issues are insurmountable. Low-profile counterweights, small base circle camshafts, and judicious grinding of the block are usually enough to provide adequate clearance for all moving components. Even so, it’s important to remember that the longer the stroke of a crankshaft, the more it pushes the limits of the available space inside a block. Generally, with careful parts selection, a production GM block can safely accommodate a 4.000- inch crank. However, some engine builders choose to take it one step further with a 4.100- or 4.125-inch stroke. Both can be made to fit, but using too short of a connecting rod can certainly pull the piston too far down the cylinder wall. In such an application, using custom pistons designed to reduce piston rock at BDC is highly recommended.
Factory Crankshafts
Most stock LS crankshafts are cast from nodular iron and have proven to be very durable in high-horsepower applications. They boast rolled fillets on the rod journals for improved strength and variable-radius undercuts on the counterweights for increased surface area. Many hot rodders have pushed stock cast cranks to 500 hp and 7,000 rpm without failure. Unlike Gen I small-block engines that were manufactured with a variety of main journal diameters, multiple rear main seal designs, and both internal and external balancing, LS engines have a crankshaft design that is far more universal. That means there’s a great deal of interchangeability, which simplifies the process of building a stroker motor. The majority of factory LS crankshafts utilize a 3.622-inch stroke; the only exceptions are the 4.000-inch units found on the LS7 and the 3.267-inch cranks used in 4.8L truck motors. All Gen III/IV crankshafts share 2.559-inch-diameter main journals and 2.100-inch rod journals. The LS7, LS9, and LSA are the only LS small-blocks equipped with forged crankshafts from the factory.
A longer stroke pulls the piston farther down the bore at BDC, decreasing the clearance between the counterweights and the piston skirts. Making sure there are no interference issues is a balancing act among counterweight height, piston skirt design, and connecting rod length.
The 4.000-inch LS7 crankshaft is the longest crank ever used in any Chevy small-block of any generation. It’s forged from 4140 steel and features a crank snout that’s nearly 1 inch longer than that of a standard Gen III/IV crank; it’s made longer to accommodate the dry sump oil pump. With the introduction of the Gen IV LS2 in 2005, GM began replacing 24-tooth reluctor wheels with 58-tooth units. (© GM Corp.)
For the most part, the 3.622-inch crankshafts used in the 5.3L, 5.7L, 6.0L, and 6.2L Gen III/IV engines are all the same. A few noteworthy differences are the thicker flywheel/flexplate flanges that were used in many Vortec truck motors and the 58-tooth (instead of the previous 24-tooth) reluctor wheels that GM began phasing in with the introduction of the Gen IV small-block in 2005. Also, all LS-series crankshafts built prior to 2009 have a universal six-bolt flywheel/flexplate pattern. From 2009 onward, the LSA uses an eight-bolt pattern, which it shares with the GMPP LSX454 crank, while the LS9 crank comes with a nine-bolt pattern.
An area of the crank notorious for failure is where the rod journal meets the counterweight. Some contend that the forging process exacerbates this condition, because it is the area where the grain flow is stretched and contorted.
Aftermarket cranks typically employ a fillet radius at the edge of the journal to relieve the area of stress risers and improve durability. This is accomplished by forcing a roller into the edge to compact the metal and create a smooth transition. A sharp, grooved edge is typical with factory cranks, but the stock LS design is an exception to the rule. In addition to a fillet radius, stock LS cranks have a variable radius undercut on the counterweights to increase bearing surface area.
None of these changes impacts performance at all. The factory computer uses the reluctor wheel to detect the position of the crankshaft, so it’s important to make sure that the wheel and computer are compatible. The aftermarket offers cranks with both styles of reluctor wheel, and the wheels can also be removed and swapped out, if necessary.
Because all LS crankshafts have the same main and rod journal diameters, they fit into any LS block. This allows bolting a 4.000-inch LS7 crank into a 5.3L, 5.7L, 6.0L, or 6.2L block for a nice bump in displacement. Unfortunately, these cranks can be difficult to balance, as they were designed to be used with superlightweight titanium connecting rods found in the LS7. Likewise, a 3.622-inch crank can also be fitted in a 4.8L Vortec motor for a gain of 32 ci, but such a swap is very uncommon in practice, because a 325-ci motor is still relatively small in the wake of stroked small-blocks. Due to the affordability of aftermarket crankshafts, they’re a much more popular alternative for stroking an engine. They’re offered in a variety of stroke lengths ranging from 3.622 to 4.600 inches.
Just as important as the extra displacement that long-arm crankshafts offer are the dividends in strength they provide. Not only does the typical stroker motor make more power than a production engine, but it also turns more RPM. As RPM increases, the bending and twisting loads transmitted through the crank jump dramatically. Stock nodular iron crankshafts were never intended to survive under these conditions, so aftermarket forgings are highly recommended for engines that produce more than 500 hp and routinely turn 7,000 rpm or more. Premium forged steel aftermarket cranks can easily handle 1,000-plus hp, and considering how easy it is to make serious power with an LS small-block, their popularity is hardly surprising.
Like the LS7’s crank, the crankshafts in the LS9 and LSA are built from forged steel. Because the crankshaft must cope with the rigors of driving a supercharger, it has a keyway integrated into the crank snout to prevent the harmonic balancer from spinning out of place. (© GM Corp.)
Cast vs. Forged vs. Billet
Two of the most important factors that determine the strength of a crankshaft are the material it’s made from and how that material is processed. Casting and forging are the two most common manufacturing methods, and each has its benefits and drawbacks. Cast cranks start life as liquid iron or steel, which is poured into a mold. This allows the raw casting to closely resemble its final shape, which reduces the amount of final machining required. Because the equipment necessary to produce cast cranks is relatively inexpensive, it’s obvious why they’re the predominant choice of the OEMs, including GM. Aftermarket cast steel cranks offer significant improvements in strength, and they can be had for as little as $500.
When comparing a cast crank (left) to a forged crank (right), it’s obvious why the forged unit fetches a higher price tag. The cast crank’s rough surface shows that very little finishing machine work is required, as the casting process yields a shape that closely resembles the end product. The forged crank’s smoother and more refined appearance reveals the extensive machining operations required after the crank leaves the forging die.
Distinguishing a cast crank from a forged unit at the swap meet or on eBay is easy. Cast cranks have a distinct parting line, a vestige from where the casting cores were separated during the manufacturing process.
In contrast, the forging process requires heavy-duty presses and more extensive final machining operations. Forging involves heating a cylindrical slug of metal to a molten state, then pounding it into shape with 200-ton presses and dies. It is this compressing action that creates an inherently stronger end product over a casting. In a casting, the grain structure is very loosely held together. In a forging, the force of the press compresses the grain together, so it becomes one uniform grain flow. As the space between the molecules is compressed, they are forced to bond together, which dramatically improves strength. In fact, forged small-block cranks routinely handle in excess of 1,000 hp.
Compared to a cast crank, the drawback of a forging is cost. The heavy-duty hydraulic presses used in the forging process cost at least $100,000, so aftermarket manufacturers must sell vast quantities of cranks before they even recover their equipment costs. This leads to a costlier product, typically about $900.
Billet cranks are closely related to forged cranks. Like a forging, a billet crank starts out as a large cylindrical ingot of steel. However, while a forged crank is compressed during the forging process, the steel ingot used in a billet crank is already forged, albeit not quite as compressed as in a forged crank. The key difference between the two is how the ingots are shaped into cranks.
The metal bar used to make a forged 4.000-inch Gen III/IV crank measures about 4.75 inches in diameter, and the crank’s total width ends up being 6.75 inches when the forging process is complete. The metal bar used in a billet crank of the same stroke is much larger at roughly 8 inches, and it weighs 350 pounds, compared to the 150-pound metal bar used to make a forged crank.
Instead of twisting and pounding the metal in different directions as done in forging, a CNC mill whittles away the metal of a billet crank into its final shape, so the grain structure runs parallel throughout the entire length of the crank. Due to the increase in materials and labor over a forged crank, billet cranks are the most expensive of them all. Custom one-offs carry price tags in the neighborhood of $3,000.
Billet cranks, like this 4.000-inch unit from Bryant Racing, offer the ultimate in strength. However, a custom billet crank costs $2,000 to $3,000, and a forged unit works just as well for most street motors at a fraction of the price.
A price tag that steep makes a billet crank impractical for the average street/strip motor. If money is no object, however, billet cranks represent the pinnacle in strength. By nature, a forging is not as strong as billet, because the forging process stretches and shears the grain structure. A forging starts out as a round bar of metal and gets twisted and turned to make the rod throws. What used to be centerline of the bar is now offset, and the grains get stretched, traumatized, and weakened, although some sections of it are substantially stronger than those in a casting. With billet, there are no stress riser areas, because the grain structure runs parallel to the length of the entire crank. Forgings are stronger than billet in bolts and axles, because the metal isn’t stretched and sheared, but not in crankshafts. The most demanding forms of racing—including NHRA Top Fuel, NASCAR Sprint Cup, and Formula One—all rely on billet cranks.
Strength
Before delving into the specifics of metallurgy, I’ll mention that there are strength characteristics universal to all castings and forgings that are worth nothing. In a lab, metal is often tested for strength by pulling a 1-inch round bar apart until it breaks. Tensile strength relates to the amount of force required to start to stretch the bar. Yield strength describes the force needed to continue to pull the bar apart. The difference between tensile strength and yield strength between castings and forgings is significant. With a casting, the cross section of the bar only needs to be reduced by 6 percent before it breaks, but with a forging, the cross section can be reduced by 20 percent before the bar breaks.
In order to balance this 4.500-inch Callies crank, several slugs of heavy metal had to be added to the counterweights. The long stroke necessitates reducing the height of the counterweights to ensure adequate piston skirt clearance, and heavy metal must be added back in to compensate for the loss in mass.
Crank overlap is simply the portions of the rod and main journals that overlap each other. Stroker cranks move the rod journal farther away from the main journal, thereby reducing overlap. Reducing the diameter of either the rod journal or the main journal decreases parasitic friction but compromises strength.
Not that long ago, entry-level forged crankshafts were built from 5140 and 4130 alloys. These days, lower manufacturing costs have enabled aftermarket companies, such as Compstar, Eagle, and Scat, to offer premium 4340 crankshafts for roughly the same price as cranks made of lesser grades of metal. Consequently, 5140 and 4130 forgings are not common these days.
Furthermore, designing a durable crank is an exercise in striking a balance between hardness and ductility. Increased hardness can lead to a stronger crank, but it still has to have some give in it so it can bend without cracking, a property that is referred to as ductility. A good way to explain ductility is by comparing glass to rubber. Glass is very hard, but it cracks easily, so it’s not ductile. Rubber bends easily, so it is very ductile, but not hard. Like a fishing pole, a crank should, ideally, give a bit under load, but it should snap back into shape without being permanently deformed. Cranks do, in fact, flex under load, and in a motor with an aluminum block, they can bend as much as .200 inch.
Where premium forged cranks shine is in their ability to be extremely hard while still maintaining ductility. The ideal crank is one that can be very hard and maintain its shape to spread bearing loads evenly throughout the crank while still having enough ductility to prevent cracking. Generally, as a crank’s hardness increases, so does its tensile strength. Having higher carbon content in steel increases hardness, but it sacrifices ductility in the process. That’s why too much carbon content in a crank isn’t always a good thing. Cast iron is the least ductile material used to build cranks, and the next step up the ladder is 5140 alloy, followed by 4130 and 4340. As you go up scale, you can increase hardness without sacrificing ductility.
Not that long ago, entry-level forged crankshafts were built from 5140 and 4130 alloys. These days, lower manufacturing costs have enabled aftermarket companies, such as Compstar, Eagle, and Scat, to offer premium 4340 crankshafts for roughly the same price as cranks made of lesser grades of metal. Consequently, 5140 and 4130 forgings are not common these days.
Metallurgy
In an alloy consisting primarily of iron, the small quantities of metal added to that iron are what determine the differences in strength between various grades of steel. A set of standards established by the American Iron and Steel Institute (AISI) determines the content of metal grades, in addition to their nomenclature. Generally, increasing the carbon content in proportion to iron improves strength. The most basic cranks are cast iron, which typically have a tensile strength of about 70,000 to 80,000 psi. Slightly increasing the carbon content of iron produces nodular iron, resulting in a tensile strength of roughly 95,000 psi. Both materials are used extensively by the OEMs, but they won’t handle the demands of aftermarket stroker crank applications. Commonly used in entrylevel aftermarket crankshafts, cast steel has greater carbon content than nodular iron and a tensile strength of about 105,000 psi.
Factory forged cranks are usually made from steel alloys, such as 1010, 1045, and 1053. Although their tensile strengths are similar to that of a cast steel crank, their elongation rating is more than three times greater. This translates to a far less brittle material. In these types of alloys, chrome and nickel are what make them stronger. There are other materials involved, but they’re used to make sure everything mixes together properly and don’t impact strength. Nonetheless, factory forgings are a far cry from the ultimate durability of an aftermarket steel crank. Factory forged steel cranks have high carbon content, but they often lack the chrome and nickel content of the premium alloys used in aftermarket cranks. Forged from 4140 steel, the cranks used in the LS7, LS9, and LSA are an exception to the norm.
Balancing is performed on machines, such as the Sunnen DCB-750 digital balancer, which is the industry standard. Essentially a glorified tire balancer, the machine holds the crank in place on two stands, and then it spins the crank and bobweights up to 750 rpm. The stands on each side detect how much imbalance exits, and the machine calculates how much weight must be removed or added to correct it.
are an exception to the norm. The most basic aftermarket-grade steel is 5140, which boasts a tensile strength of about 115,000 psi. This material used to be—and to some extent still is—an excellent choice for racers on a budget, but it is less common than it was in years past, due to the increasing affordability of premium alloy cranks. These include 4130 and 4340 forgings, which have tensile strength ratings of approximately 125,000 and 145,000 psi, respectively. Engine builders and crankshaft manufacturers universally accept 4340 as the ideal alloy for strength and durability. Because aftermarket LS 4340 cranks start at $900 for most engine platforms, the lesser grades of steel are dwindling in popularity. In fact, almost all aftermarket forged LS crankshafts are made from 4340 steel.
Overlap
Just as the term implies, journal overlap is simply how much of a crank’s main and rod journal diameters overlap. If you were to stand a crank up vertically, it can easily be seen, as the portions of the main and rod journals overlap each other. As stroke is increased, moving the rod journals farther away from the main journals reduces overlap and compromises strength and durability. To compensate for this, when GM increased the stroke from 3.480 inches to 3.750 inches in the Gen I 400-ci small-block Chevy, it also increased the size of the mains from 2.45 inches to 2.65 inches to maintain adequate journal overlap.
After the spin cycle, the crank is rotated by hand, and an encoder on the balancer very accurately measures crankshaft position to help a machinist pinpoint the exact spot where the counterweight must be modified. A digital readout on the balancer tells the operator the exact location where weight must be added or removed and the amount of the weight. Balancing to “x” number of ounces simply means how much imbalance, in ounces, exists 1 inch from the crank centerline.
Drill char ts from crank manufacturers specify how much weight a given drill size and drill depth will remove. Because the crank acts as a lever, the farther away from the centerline weight is removed or added, the greater effect it has on balance. Typically, balancing takes 1 to 11⁄2 hours to perform.
With today’s lightweight rods and pistons, weight is removed from the counterweights the majority of the time when balancing a rotating assembly. If an unusually large amount of weight must be removed, the counterweights can either be Swiss-cheesed with a bunch of holes or be turned down in a lathe.
However, with improved modern alloys, crank overlap isn’t as important as it used to be. For instance, GM was able to maintain the same main and rod journal diameters throughout the Gen III/IV family when it increased the stroke to 4.000 inches in the LS7. A common practice in high-end race motors is to run smaller rod and main journals to reduce the surface area of the bearings. This, in turn, reduces friction and can increase power, but it also reduces overlap. It also requires either turning down the crank journals or ordering a custom billet crank, and both options are very expensive. Unless you’re racing in a class where 5 hp can determine the winner of a race, sticking with factory LS main and rod journal diameters makes the most sense.
Twist vs. Non-Twist Forging
Forged cranks are pressed into place on a die, but there are two different techniques used to accomplish this. The simplest method is to forge one of the crank throws at a time in a flat forging die. The crank is then twisted, and the die forges the next throw. Conversely, in a nontwist forging, all four throws are forged simultaneously, which requires a more complex die. Non-twist forgings are said to reduce internal crankshaft stresses during the manufacturing process, but whether or not that’s true is up for debate. If all variables are controlled properly during the forging process, there’s little, if any, difference between twist and non-twist forgings. Most aftermarket cranks these days are non-twist forgings anyway, so there’s no sense in arguing either way.
Heat-Treating the Crankshaft
In addition to materials and casting or forging techniques, heat-treating can greatly impact the strength of a crankshaft. Nitriding is the most prevalent method of heat-treating used in aftermarket cranks; it is where ionized nitrogen is vacuum-deposited onto the crank surface in an oven. By penetrating .010 to .012 inch into the metal surface and changing the microstructure of the steel, surface hardness is doubled from 30 to 60 on the Rockwell scale, and fatigue life is increased by 25 percent. Although the process does strengthen the crank a bit, improving the impact and wear resistance is the real benefit of nitriding, and this reduces the potential for cracking. That’s very important, because impact and wear are the most common causes of crank failure.
The older method of heat-treating is induction-hardening, in which the journals are heated using a magnetic field and then plunged into water. This results in deeper penetration into the metal surface (.050 to .060 inch), but it is more localized than with nitriding, which treats the entire crank at once. Inductionhardening can be performed with cheaper equipment, so it’s usually the method of choice for the OEMs. However, if the rate of cooling isn’t carefully controlled, it can create stress risers and soft spots. For this reason, most aftermarket crankshafts are heat-treated through the nitriding process.
Knife-Edging the Crankshaft Counterweights
For decades, hot rodders have maintained that knife-edging a crank’s counterweights reduces windage, and, therefore, increases horsepower. However, this is more of an old wive’s tale than reality. The theory is that because oil is viscous and has resistance, a crank that’s more narrowly profiled slices through it more easily. However, with windage trays and today’s low-profile oil pans, like the ones used in LS smallblocks, windage isn’t much of an issue. In reality, knife-edging was developed more for ease of balancing than power and won’t increase horsepower much at all on a street motor. Oil hits a knife edge and gets thrown all over the place when it should ideally land on the nose and flow off to the side, like snow on a snow plow blade. A bull-nose rounded leading edge is the most efficient, like the bow of a ship, and it is the design more commonly used in modern crankshafts.
Balancing the Crankshaft
In every performance engine build, the crankshaft must be balanced to match the rest of the rotating assembly. Otherwise, a motor can literally rattle itself to death. By nature, a 90-degree V-8 isn’t the smoothest-running engine configuration, so balancing a performance rotating assembly requires some extra precision.
When balancing a rotating assembly, the goal is to make the reciprocating mass equal to the rotating mass. This yields a smoothly running motor free of unwanted vibrations that reduce bearing life. With today’s lightweight aftermarket pistons and rods, weight is removed from the counterweights the majority of the time. Only in applications where extremely heavy-duty nitrous or blower parts are used, or where space constraints reduce the size of the counterweights, is weight added.
It’s a common misconception that bobweights simply duplicate the weight of a pair of pistons and rods. Bobweights are actually equal in mass to 100 percent of the rotating weight (big rod ends and rod bearings) and 50 percent of the reciprocating weight (pistons, pins, locks, and small rod ends). In a 90-degree V-8, each piston has a companion piston it travels with to TDC at the same time. So, to equalize rotating and reciprocating weight, only half the total reciprocating weight is taken into account when balancing. After carefully measuring both the rotating and reciprocating weights, bobweights are selected that match that formula when balancing a crankshaft.
Many manufacturers drill holes through the rod and main journals to reduce weight. The amount of weight that’s reduced isn’t as important as the location the weight is removed from. Drilling the main journals removes mass from the centerline of the crank, but it doesn’t do much at all for performance. Conversely, removing weight from the rod journals and counterweights reduces rotating mass, which is far more effective. That said, lightweight cranks do little to improve the performance of the average street/strip motor.
When balancing a rotating assembly for a street motor, the goal is to equalize the rotating mass and the reciprocating mass. However, in race motors, it’s not uncommon to overbalance the crank. A balancer generally spins a crank 500 to 750 rpm, and for obvious safety reasons, you can’t replicate the actual RPM the crank experiences in a running engine. However, if you spin a motor at very high RPM, say 7,000 to 8,000 rpm, parts can stretch and move around. Aluminum rods might stretch as much as .030 inch. This stretch increases load on the crank and bends it, making the pistons and rods behave as if they’re heavier than they really are, due to dynamic inertial effects.
To the crank, the pistons feel heavier, so if you have a rotating assembly that calls for a bobweight of 1,800 grams, a motor may run more smoothly if you overbalance the crank by 2 percent. This compensates for the inertial loads the crank endures at high RPM by balancing the rotating assembly to a bobweight of 1,836 grams instead of 1,800 grams. Although the balancer indicates that the crank isn’t balanced, the bearings actually look better when you tear the motor down.
On a 6,500-rpm street motor, there’s no need to overbalance. It’s more for race engines that run 7,000 to 8,000 rpm all day. When in doubt, it’s advisable to consult with your machinist to see if overbalancing is necessary.
Crankshaft Weight
Many hot rodders are under the impression that reducing crankshaft mass equates to an increase in horsepower. Although that can hold true in some instances, not all lightweight cranks are created equal, and few street/strip engines can actually benefit from them. The theory is that a lightweight crank has less rotating mass and is, therefore, easier to accelerate, which increases horsepower. However, the overall weight of a crankshaft is less important than how and where that weight is allocated throughout the crank.
Simple physics dictate that the farther weight is from the centerline of the crankshaft, the more difficult it is to turn. Consequently, removing weight from the centerline of a crank does nothing for performance. On the other hand, there are gains to be had by removing weight from the crank throws and counterweights, thereby reducing rotating mass, as long as it doesn’t compromise the strength of the crank.
The effect is similar to running a lightweight flywheel. On a street car, you may notice slightly improved acceleration, but lightweight cranks aren’t really intended for street cars, or drag cars, for that matter. In circle track and road race applications, where a motor is moving up and down the powerband over and over again and maximum acceleration on corner exits is important, a lightweight crank makes more sense. Of course, lighter cranks also decelerate more quickly, which in circle track application can unload the suspension too quickly when entering a corner.
Reduced rotating mass also relieves main bearing loads and puts less stress on the block. However, in drag applications, a lightweight crank probably won’t determine the winner of the race, and the extra money it would cost to buy one is better spent on cylinder heads. Moreover, if a lightweight crank isn’t matched with a lightweight rotating assembly, it could require adding heavy metal to the counterweights for proper balancing. So without careful planning, it’s possible to spend lots of money on a lightweight crank, only to have to put weight back into it during the balancing process.
Dampeners
Four-stroke internal-combustion engines operate by converting the reciprocating motion of the pistons and connecting rods into rotating motion. This process naturally sends vibrational pulses into the crankshaft every time each cylinder fires. At a certain RPM, these pulses start to resonate and can literally destroy the crankshaft. To prevent this from happening, all production engines come equipped with harmonic balancers attached to the crankshaft snout to dampen these vibrations. Stock balancers work just fine at stock horsepower levels, but as output and RPM increase, a more rugged unit is always a good idea. Interestingly, street motors are more susceptible to uncontrolled resonant harmonics, because they spend more time at a sustained RPM. By comparison, drag and road race engines that are constantly moving up and down the RPM range are less vulnerable.
In engine combos exceeding 600 hp, an aftermarket balancer is a wise investment. The ATI Super Damper is a favorite of many engine builders, and it is SFIapproved for competition use.
Stock GM harmonic balancers are of an elastomeric design that sandwiches vulcanized rubber between a pair of rings. Car and truck LS variants use different balancers, but these units have proven to be extremely durable and effective up to 600 hp. There really is no definitive point at which an aftermarket harmonic balancer is necessary, but they do offer a greater degree of dampening ability in high-horsepower applications. Some aftermarket units are filled with viscous fluids, and others are similar in principle to GM’s elastomeric design. Because the centrifugal force a dampener must endure increases significantly as engine speed rises, there is a risk that a stock balancer can self-destruct at high RPM. For safety concerns, many sanctioning bodies require SFI-approved aftermarket balancers in certain racing classes.
Manufacturer Choices
With the basics of crankshaft design covered, it’s time to take a closer look at the specific cranks offered by the aftermarket. Although it’s impossible to list every LS crankshaft on the market, here’s a breakdown of the most popular stroker cranks. Whether it’s due to durability, overall value, or reputation, many LS enthusiasts rely on these cranks for stroker builds.
Callies Crankshafts
For more than two decades, Callies crankshafts have been synonymous with bulletproof performance. Today, the company offers premium domestic cranks under its Callies brand and more affordably priced off-shore cranks under its Compstar banner. For Gen III/IV applications, Callies’ entry-level Dragonslayer cranks are offered in 3.625- and 4.000-inch strokes. Made of forged 4340 steel, these feature drilled main and rod journals, nitrided wear surfaces, and have roundness and taper tolerances held within .0003 inch. While Callies doesn’t publish an official maximum horsepower rating for its Dragonslayer crankshafts, they have proven reliable in 1,800-hp drag cars.
Moving up the ladder, Callies Magnum and Magnum XL cranks offer many of the same features of the Dragonslayer lineup, but in a lightweight package. They’re available in strokes up to 4.600 inches and have a unique counterweight design that spreads balance forces evenly throughout the entire length of the crank for improved bearing life. For LS7 and LS9 engines, Magnum cranks are available with longer snouts to maintain compatibility with the factory dry sump oil drive system. A 4.000-inch Magnum crank weighs 47 pounds, and Magnum XL cranks can weigh as little as 36 pounds. For the ultimate in strength and customizability, Callies also offers Ultra Billet cranks. Made from Timken steel, they can be tailored to just about any configuration imaginable.
Designed for sportsman racers, Compstar cranks are forged overseas and imported to the United States, where Callies performs the finishing machine work in-house. Forged from 4340 steel, Compstar cranks feature profiled counterweights, drilled rod journals, and nitrided wear surfaces. They’re available in strokes up to 4.250 inches and in both 2.100- and 2.000-inch rod journal diameters. Compstar’s Sportsman label can be a bit misleading, as these cranks routinely handle in excess of 900 hp.
Eagle
Ever since overseas crankshafts started hitting the hot rodding scene in the late 1990s, Eagle has established itself as one of the market leaders. Much of that has to do with the quality and diversity of products the company offers. As is common in the industry, Eagle sources its forgings from overseas, and then performs the final machine work at its Mississippi facility. For the LS-series small-block, Eagle’s catalog is packed with 4340 steel nontwist forgings in 3.622-, 4.000-, 4.100-, 4.125-, 4.250-, and 4.375-inch stroke lengths. Rated at an impressive 1,500 hp, Eagle cranks are shot-peened and nitrided, and they also boast micro-polished wear surfaces. To simplify the stroking process, Eagle bundles together its cranks and rods with pistons and bearings from leading manufacturers to offer turnkey rotating assemblies.
Lunati
Lunati’s LS-series crankshafts are 100 percent made in the United States. The company’s Pro Series crankshafts are some of the highest quality forgings on the market, and they come in 3.622-, 4.000-, 4.125-, 4.185-, 4.250-, 4.500-, and 4.600-inch sizes. They’re constructed from 4340 aircraft-grade steel to ensure optimal levels of cleanliness and purity. Journal roundness is kept within .0001 inch, and Lunati cranks feature lightening holes drilled into the rod journals. Other highlights include contoured counterweights and polished-and-inductionhardened bearing surfaces. According to Lunati, the Pro Series cranks easily endure 1,500 hp of punishment.
Crankshaft end play should be set at .005 to .008 inch because too much fore-andaft crank movement can prematurely wear out the bearings. Since the thrust bearing is located on the number-3 main cap, end play is measured with the center cap torqued down.
Manley
Although best known for highquality valvetrain components, Manley also offers a line of crankshafts for Gen III/IV small-blocks. These 4340 steel forgings come in two stroke lengths, 4.000 and 4.100 inches. All Manley cranks are shoot-peened and stress-relieved with profiled counterweights and polishedand-drilled journals. They’re available in lightweight and super-lightweight designs, which weigh 50 and 46 pounds, respectively. Manley cranks are slightly less expensive than competing designs, making them a great value.
Scat
During the development phase of the LS-series small-block, GM turned to Scat to manufacture the cranks and rods in its prototype engines. Scat was one of the first companies to release aftermarket LS crankshafts. Today, Scat offers high-quality forged 4340 steel crankshafts in 4.000-, 4.125-, and 4.250-inch strokes. Scat’s entry-level standard-weight cranks boast profiled counterweights, straight-shot oiling holes, large-radius journal fillets, lightening holes, and nitrided bearing surfaces. The mid-level Pro Comp cranks feature aero-wing counterweights for reduced mass and windage. The top-ofthe-line Superlight cranks add pendulum undercuts on the inner face of the counterweights to further reduce mass without sacrificing strength. For most street/ strip applications, Scat’s standard-weight cranks provide the best value and can handle more than 1,000 hp. The company can also custom-build billet cranks in any configuration imaginable, but be prepared to spend more than $3,000.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
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