Читать книгу LS Gen IV Engines 2005 - Present - Mike Mavrigian - Страница 9
ОглавлениеCHAPTER 3
CRANKSHAFTS AND CONNECTING RODS
All Gen III and Gen IV crankshafts share a similar design, but construction materials, stroke length, and engine oiling system requirements differ among versions. Most OEM LS crankshafts are made of cast iron, except for stronger forged cranks used in the LS7 and LS9 engines. LS2, LS3, and LS9 cranks feature a 3.62-inch standard stroke, while the LS7 crank features a 4.00-inch stroke. To accommodate the oil pump drive on LS7 and LS9 engines, the crankshafts feature a snout that’s about 1 inch longer than other LS crank snouts. What remain the same among all LS cranks are main journal diameters of 2.65 inches and rod journal diameters of 2.10 inches. All LS cranks also accept the same one-piece rear main seal. All rod journals have the same spacing to accommodate the block’s 4.400-inch bore spacing, and all LS blocks feature the same cylinder bore spacing.
The crank should always be treated to a balancing job when swapping an LS crank from one version to another, regardless of what pistons and rods are to be used, and whether using GM or aftermarket pistons and rods. Never assume that the crank is accurately balanced, even if you intend to use rods and pistons that were originally part numbered for a specific crankshaft. Spending $150 to $250 or so for a balancing job is well worth the investment to verify correct balance. An out-of-balance crankshaft can quickly result in catastrophic damage to the crank, rods, pistons, bearings, and potentially even the block.
Crankshaft Specifications
| Crankshaft Stroke | |
| 6.0L LS2 (364 ci) | 3.62 inches |
| 6.2L LS3/LS9 (376 ci) | 3.62 inches |
| 7.0L LS7 (427 ci) | 4.00 inches |
| Crank Journals | |
| Main journal diameter | 2.650 inches |
| Rod journal diameter | 2.100 inches |
| Crank Flange | |
| 2006–2008 LS2 | Six-bolt |
| 2009 and later LS | Eight-bolt |
| 2009 and later LS9 | Nine-bolt |
| GM Crankshaft Part Numbers | ||
| Type | PN | Cast/Forged |
| LS2 | 12588612 | Cast iron |
| LS7 | 12611649 | Forged steel |
| LS3 | 12597569 | Cast iron |
| LS9 | 12603616 | Forged steel |
| Crankshaft Position Sensor | ||
| Gen III | Black (for 24-tooth reluctor wheel) | PN 12560228 |
| Gen IV | Gray (for 58-tooth reluctor wheel)* | PN 12585546 |
| *The LS9 sensor is specific to the LS9, as PN 12601389. |
All LS crankshafts are cast iron except for the LS7 and LS9 forged-steel units. The cast cranks feature a main journal diameter of 2.650 inches and a rod journal diameter of 2.100 inches.
While GM OEM cranks accept the crank pulley as a press-on fit with no indexing keyway, aftermarket performance cranks usually do include a front key to accept a keyed crank balancer. If you plan to run a keyed aftermarket balancer such as ATI or Fluidampr, make sure that the crank has a front keyway.
Crankshaft Reluctor Wheel
The crankshaft reluctor wheel, often referred to as a “tone” wheel, features a precision-spaced number of teeth along the circumference, which provides a timing reference for the ECM. As the crankshaft rotates, signals produced as the reluctor wheel passes by the stationary crankshaft position sensor relay the crankshaft’s position to the ECM. In combination with the camshaft position sensor, these signals provide the ECM with information used to regulate ignition spark timing and fuel injector timing. The reluctor wheel is interference-fit to the rear crankshaft flange.
Both OEM and aftermarket crank snouts feature a key to locate the oil pump drive gear. Aftermarket cranks are available with or without a damper key. If you plan to run a keyed aftermarket damper, the crank snout must feature a front key.
All Gen IV cranks feature a 58-tooth reluctor wheel. When purchasing a new crank, make sure that the reluctor wheel is already installed. If you buy a crank and the wheel is separate, a special indexing tool is required to position the wheel in the correct clock position. Goodson Tools & Supplies offers such a tool. The wheel is carefully pressed into position. Never hit or tap the wheel, which is easily distorted. The wheel should never move if properly interference-fit. Some builders prefer to add a tack weld to secure it from potential rotation.
If a tone wheel is damaged, or if you purchase a crankshaft that was shipped without the tone wheel already installed, a special tone wheel indexing tool is essential.
The tooth count of the reluctor wheels began with 24-tooth versions and evolved to the use of 58-tooth versions. The greater number of teeth provide a slightly more precise timing signal, allowing the ECM to control spark more. To provide a relative example, think of it as a desktop computer that has a stronger processor for faster and more accurate processing.
In practical terms, it really doesn’t matter which tooth count you have, as long as the ECM is compatible and designed to work with that specific tooth count. For instance, if you’re buying an aftermarket ignition controller for an LS application, you simply need to choose the 24-tooth or 58-tooth controller, based on the tooth count of your crankshaft’s reluctor wheel. If you have a 24-tooth wheel and for some reason you wish to change to a 58-tooth wheel, the reluctor wheel may be swapped out. Be aware that a special indexing tool is necessary when installing a wheel to the crank, to properly index the wheel. This special tool is available from suppliers such as Goodson Tools & Supplies.
A special tool fixture is required to install a reluctor/tone wheel to an LS crank. The Goodson Tools & Supplies reluctor wheel installation tool, PN RRJ-350 Reluctor Ring Jig, will work with either the 24- or 58-tooth wheel (24-tooth wheel seen here).
The crankshaft position sensor mounts to a smooth-bore hole on the right rearward side of the block. This hole aligns to the teeth of the reluctor wheel. Gen III sensors are black in color, while Gen IV sensors are gray. Gen III sensors are suited to 24-tooth tone wheels, while Gen IV sensors match to 58-tooth wheels.
Some early Gen IV engines feature a 24-tooth crankshaft reluctor wheel (2005 LS2 Corvette, 2005–2006 LS2 GTO, 2005–2006 LS2 SSR), GM part number 12551520 or 12559353. Later Gen IV engines feature a 58-tooth reluctor wheel (2006–2007 LS2 Corvette, 2006–2009 LS7 Corvette, 2008–2009 LS3 Corvette, etc.), as GM PN 12586768.
Note: The LS9 crankshaft reluctor wheel also features 58 teeth, but it is slightly smaller in diameter and requires a different crank position sensor. As of this writing, General Motors apparently does not have the specific reluctor wheel for the LS9 available as a service part. However, the LS9 crankshaft position sensor is available as PN 12601389.
The installation tool features an 8-mm locating dowel that engages into the tone wheel and is located on a welded tang on the outside of the tool body.
The registering tool’s internal locating pin provides a high-precision fit into the hole in the crank flange.
With the wheel heated and affixed to the tool, the wheel will easily slip onto the crank flange. Note that the tone wheel is indexed on the crank with the two arrowhead-shaped holes at 90 degrees to the first rod pin, with the series of large holes in the wheel positioned opposite from the first rod pin. However, you simply cannot install the wheel by eyesight alone. The specialty tool is mandatory to properly locate the clock position of the wheel.
Inside the tool body is an internal dowel that locates into the crankshaft’s rear flange dowel hole.
Note how the installation tool’s outer dowel pin precisely engages into the tone wheel’s 8-mm indexing hole.
Crank Snout Length
Dry sump engines such as LS7 and LS9 feature longer snouts, approximately 1 inch longer than other LS crank snouts, to accommodate the dry sump drive.
Standard (wet sump) crank snout length is 3.3880 inches. LS7 and LS9 dry sump crank snout length is 4.2740 inches. Dry sump and supercharged applications require a longer crankshaft snout to accommodate the dry sump oil pump drive.
Note: Main crank journal and main bearings are the same size for all LS engines. The only difference with the GM main bearings for LS7 and LS9 applications is the addition of an antifriction bearing coating. If buying aftermarket main bearings (in standard size), an example is the Clevite MS-2199HK. These bearings are available coated.
Here’s a comparison of crankshaft snout length between LS1/LS6/LS2/LS3 cranks and LS7/LS9 cranks. The snout length of most LS cranks is 3.3880 inches, while the snout on LS7 and LS9 cranks is longer, at 4.2740 inches, to accommodate the dry sump drive. The bevel for the crank gear is identical on all LS cranks, at .8910 inch deep. (Photo Courtesy Callies Crankshafts)
GM Bearing Part Numbers
| Main Bearings | GM Part Number |
| All except LS7/LS9 | 88894271 |
| LS7/LS9 | 89017877 |
| Main thrust (except LS7/LS9) | 89017572 |
| Main thrust LS7/LS9 | 89017808 |
Connecting Rods
All OEM connecting rods for LS engines are made of powdered metal except the rods for LS7 and LS9 engines, which are forged titanium. Powdered metal rods are surprisingly strong and are generally acceptable for horsepower applications up to around 400 to 450 hp. For higher-horsepower assemblies, it is strongly recommended to upgrade to quality aftermarket forged-steel rods, such as those offered by Scat, Eagle, Callies, Lunati, Manley, and others.
Rod-to-piston design changed as well from earlier models. Pre-2006 rods featured a press-pin design, while 2006 and later feature a floating pin design that has bronze bushings installed in the rod small end and retaining clips to secure the wrist pins.
The LS7 rod small-end front and rear outer surfaces are machined at a partial relief cut angle to accommodate the LS7 piston pin boss design, so you can’t use OEM LS7 pistons with rods from a different version. Another unique aspect of the OEM LS7 and LS9 titanium rods involves the rod big-end bore diameter, which differs from other LS rods. Although the crankshaft rod journals are the same diameter as other LS cranks, the LS7 and LS9 rod bearings require GM PN 89017811, as opposed to LS1/LS2 rod bearings under GM PN 89017573 (or equivalent crossover to aftermarket bearings).
Keep in mind that we’re talking about OEM parts. When dealing with performance aftermarket rods, rod bearing OD may be identical regardless of the engine version.
Rod Bearings
Aftermarket rod bearings are readily available. An example is the Clevite CB-663HNK (standard size). Rod bearings are offered in a variety of under and over sizes. CB-663HX bearings, for example, are slightly thinner, allowing an extra .001 inch of oil clearance (or when mixed with a standard bearing on the same journal, this provides an added .0005 inch of oil clearance). Under sizes for reground crank journals are also available.
While most LS engines feature powdered metal connecting rods, a performance upgrade should include a set of forged-steel H-beam rods. The factory PM rods are actually very strong, but if horsepower expectations exceed around 450 hp, upgrading to forged-steel rods is recommended.
Powdered metal rods (known as PM rods) are pressure cast as one piece. The parting line is then created by snapping off the cap. This creates an uneven and unique mating surface for each rod and cap. When assembled, the cap registers perfectly to the rod because of its unique “fingerprint.”
PM rods are also known as “cracked cap” rods for an obvious reason: the method involved in separating the rod cap. The interlocking nature of the cap-to-rod mating provides a very accurate alignment.
As mentioned earlier, factory original LS7 and LS9 applications utilize a different thickness of rod bearing due to the unique LS7 and LS9 rod big-end diameter.
Several respected performance aftermarket manufacturers offer upgraded crankshafts and connecting rods for the LS family of engines. Enhancements over OEM components include high-density forgings; a wide selection of crank strokes and rod lengths; choices of I-beam or H-beam rod designs equipped with high-strength rod bolts that are installed by torque rather than torque-plus-degree tightening; lighter-weight rotating assemblies; and more. Offerings in terms of stroke length and rod length allow the builder to achieve the stroke desired for an application. Rods for LS cranks feature on-center bores with no offset to accommodate LS rod pin spacing.
High-quality, high-strength aftermarket rod bolts such as those made by ARP are not torque-to-yield and can be reused. This eliminates the need to perform a torque-plus-angle tightening, as these are designed for a straight torque application. Also, each end of the rod bolt (shank tip and head) features a centered dimple that allows the use of a rod bolt stretch gauge to monitor bolt stretch during installation for a more precise clamping load.
OEM and aftermarket full-float piston pin applications feature a bronze bushing. A full-float pin design reduces friction, making it applicable regardless of horsepower level. However, in my opinion, if you plan a build to exceed around 400 hp, a full-float wrist pin system should be considered mandatory.
All Gen III and Gen IV rod and piston combinations feature powered metal connecting rods and hypereutectic cast pistons except the LS7, which features titanium rods and hypereutectic pistons, and the LS9, which features titanium rods and forged-alloy pistons. Forged pistons are required to withstand the higher cylinder pressures caused by supercharging. Shown here is a powdered metal rod and hypereutectic piston. Piston wrist pins are interference-fit to the pistons except for the LS7 and LS9 applications, which feature a full-floating pin.
A performance upgrade of aftermarket rods and pistons will benefit any Gen III or Gen IV build. Various rod lengths and piston compression heights are available to suit any bore and stroke combination. While OEM powdered metal rods and hypereutectic pistons are reasonably durable, if you plan to exceed 450 hp, upgrading to forged rods and pistons is highly recommended. The same applies to forced induction. If you plan to apply serious boost, or if you plan to use nitrous oxide injection, moving to these stronger components is critical.
Aftermarket performance connecting rods feature laser-etched numbers on one side of the big end. If rods and rod caps happen to be mixed up during any rod service, during assembly these matching cap-to-rod numbers allow you to verify the correct cap for any specific rod. Also, since the numbers appear only on one side, this helps to identify cap orientation to the rod. Of course, one side of the big-end bore will feature a larger chamfer, which always faces the crank journal fillet, so the chamfer of the rod saddle and cap must be identical when assembled.
The LS7 OEM connecting rods are made of forged titanium, primarily due to their lighter weight. Note the beveled area of the rod small end, which is designed to accommodate the pin boss bracing of the LS7 OEM piston. Unlike other LS series powdered metal rods that feature a cracked-cap design, where the cap is separated from the rod to provide a perfect mating match-up with no machining required, the LS7 titanium rods feature traditional machined surfaces that are honed to round.
Rod Length
One big difference among Gen IV LS rods involves rod length (center of the wrist pin bore to center of the big-end bore). The 6.0L (LS2) and 6.2L (LS3 and LS9) engines originally used a rod length of 6.098 inches, while the 7.0L (LS7) rod length is 6.067 inches. If moving to a longer crankshaft stroke, rod length will vary to work with the combination of block deck height, stroke, rod length, and piston compression distance (piston CD). Depending on crankshaft stroke and piston CD, listed here are minimum rod lengths based on stroke. Given a stock block deck height of 9.240 inches, the remaining variable will be piston CD:
| Stroke | Minimum Rod Length |
| 4.000 inches | 6.100 inches |
| 4.125 inches | 6.125 inches |
| 4.250 inches | 6.300 inches |
| 4.450 inches | 6.300 inches |
| 4.600 inches | 6.300 inches |
Crank Stroke and Rod Length
If cylinder bore diameter and crankshaft stroke are equal, the engine is referred to as being “square,” with a stroke/bore ratio of 1:1. If the cylinder bore diameter is greater than stroke, this is called “oversquare.” If stroke is greater than cylinder bore diameter, this is called “undersquare.” With an undersquare combination, by increasing the crankshaft stroke, peak torque is created at a lower RPM range and piston speed increases at higher RPM. By increasing bore diameter and/or stroke, you increase engine displacement.
Determining the proper crank stroke, rod length, and piston compression distance directly affects the piston deck height in a specific block. For example, an LS block with a deck height of 9.240 inches (crankshaft bore centerline to head deck surface) requires a crank stroke, rod length, and piston pin height combination that will achieve an assembled deck height that does not exceed the block’s deck height; otherwise the piston would be above block deck at TDC. Most OEM LS blocks feature an assembled deck height that would bring the piston dome to .005 to .010 inch below the block deck. After machining to square the block decks to correct for factory tolerances, it’s not uncommon for assembled deck height to bring the piston .005 to zero the deck height.
As an example, we’ll pose a zero-deck assembly for the sake of illustration. When considering assembled deck height, we need to factor only half of the stroke because we only want to consider the distance/length from the crank’s rod journal at TDC to the block deck.
Here’s a simple formula:
(Stroke Divided by 2) + Rod Length + Piston Pin Height = Assembled Deck Height
Using a 4.000-inch-stroke crankshaft with 6.125-inch rods and piston pin height at 1.115 inches:
(4.000 Divided by 2) + 6.125 + 1.115 = 9.240 inches
If the required block deck height is 9.240 inches, the example package that includes a 4.000-inch stroke, 6.125-inch rods, and 1.115-inch piston pin height would result in a theoretical assembled deck height of 9.240 inches, which would result in a zero deck.
If you decide to increase crankshaft stroke, clearances must be checked as mentioned earlier, including crank counterweight to block pan rail, piston skirt to counterweight, rod big end to block pan rail and bottom of bores, and rod big end to camshaft lobes.
Aside from clearance issues, we need to understand the effect of connecting rod ratio, which involves the leverage effect of the rod relative to the crankshaft. Rod ratio is represented by rod length divided by crank stroke.
An example of a stroker combination that features 6.125-inch rods and a 4.000-inch stroke would be a rod ratio of 1.53:1. Compare this to an OEM LS3 package that features a stroke of 3.62 inches and rod length of 6.098 inches, which has a rod ratio of 1.68:1.
As rod ratio is lowered, rod side-loading increases. Side-loading can be understood by imagining that the piston is being shoved against the thrust side of the cylinder wall in addition to traveling up and down through the cylinder. Increased side-loading places additional friction between the piston skirt and cylinder wall. But maintaining a rod ratio within reasonable limits of about 1.44:1 shouldn’t be a concern as long as proper cylinder wall clearance, cylinder wall finish, the use of stronger aftermarket forged pistons, and recommended piston rings are adhered to. Granted, certain race-only packages may call for shorter stroke and higher rod ratio, but for street or street/race setups, you should be fine sticking within the stroke and rod length combination limits recommended and offered by performance aftermarket manufacturers. In short, if you want more torque at lower RPM, the bigger the bore and longer the stroke, the better.
Determining Displacement Based on Stroke and Bore Diameter
It’s easy to determine theoretical engine displacement with one of two simple formulas. The first formula uses .7854, a factor of pi:
Bore × Bore × Total Stroke × .7854 × Number of Cylinders
Example using a 4.125-inch bore diameter and a 4.000-inch stroke in a V-8 engine would look like:
4.125 × 4.125 × 4.000 × .7854 × 8 = 427.65 ci
An alternative formula for a V-8 engine using the same bore and stroke is as follows:
Bore × Bore × Total Stroke × 6.2838
4.125 × 4.125 × 4.000 × 6.2838 = 427.69 ci
Aftermarket Connecting Rods
Selecting the most suitable connecting rods for your build is essential. Nearly all stock LS connecting rods are made of powdered cast metal, so when high-horsepower engines are built, owners often upgrade to forged or billet rod in H- or I-beam construction. Titanium rods are installed in the LS7 and the LS9.
The connecting rod is under enormous stress and must support the power output of the engine; therefore, you need to install a connecting rod that meets or exceeds the engine’s requirements. OEM powdered metal rods are adequate for medium-HP street builds, but if you plan for more than 400 hp, it is strongly recommended to upgrade to forged-steel connecting rods. When deciding between H-beam or I-beam rods, an I-beam design is slightly lighter than an H-beam rod, making an I-beam perhaps more desirable in terms of higher RPM. However, while an H-beam rod may be slightly heavier, the H-beam design offers greater rigidity and stiffness more suitable for high-torque applications and is able to better withstand high compressive force. Aluminum, billet, and titanium rods offer lighter weight but come at a higher cost. For the majority of high-performance street builds, forged-steel H-beam rods are generally the best choice, considering both durability and budget.
Callies
Callies has a rod selection that includes Ultra XD, Ultra H-Beam, Ultra I-Beam, and Compstar lines in both H- and I-beam construction. There are sizes for 2.100-inch rod journals.
Brian Crower
The Pro Series H-Beam features 4340 steel with radial grooved pin bushings, a lightening hole above the big end, and double-ribbed cap for added strength. Lengths include 6.100 inches and 6.125 inches.
Eagle Specialty Products
Eagle offers a range of H-beam and I-beam rods for LS fitments. Within its LS Series, lengths include 6.100, 6.125, 6.200, 6.250, 6.460, and 6.560 inches, all with .927-inch wrist pins. The standard rod pin size is 2.100 inches, but lengths of 6.460 and 6.560 are also available for 1.8890-inch rod pins. The LS Series for L92 heads includes I-beam design in a 6.125-inch length. The company also offers applications for the LSX tall-deck 9.700-inch block and for the LS World Warhawk 9.800-inch-deck block.
GRP Connecting Rods
GRP specializes in billet-aluminum and billet-titanium rods, made to order. Billet rods are completely CNC-machined to the builder’s specifications, so center-to-center lengths and bore diameters can be achieved per the builder’s wishes. High-density forgings are CNC-machined to shape. Center-to-center distance is CNC-machined to within .0002 inch. Final bore sizing is also finished to the same tolerance. The rods are then highly polished to remove any potential stress risers. Consider billet-alloy rods only for extreme racing applications.
K1 Technologies
K1 offers a steel-billet H-Beam in either 6.098-inch or 6.125-inch center-to-center lengths. It’s difficult to place a horsepower rating on connecting rods. Performance rods are designed, including material of choice, profile, and dimensions, to handle high loads experienced in high-performance and racing applications. Several variables affect the rod’s ability to handle high loads, including peak operating RPM, weight of the piston, and crankshaft stroke. Heavier pistons, higher engine speed, and longer crank stroke are all factors that increase inertia loads on the rods. If we’re speaking in very broad generalities, high-quality forged rods should be able to withstand up to about 1,000 hp, but again, this is assuming that the rods are not overloaded, that bearing clearances and oil delivery were not compromised, and that rod caps have been properly tightened with the appropriate rod bolts at the correct torque value while not exceeding rod bolt stretch limits.
Lunati
The company’s Voodoo Series rods feature H-beam design, while the Signature Series rods feature I-beam. All Lunati LS rods are offered in lengths of 6.125, 6.250, 6.300, and 6.400 inches. All accommodate a 2.100-inch journal size. All rods are CNC-machined forgings of 4340 steel. A number of variables affect the connecting rod’s ability to withstand the inertia loads produced by piston weight, length of crank stroke, and engine speed, in addition to engine tuning and piston-to-head and piston-to-valve clearances. When combustion occurs, the piston is pushed down, placing a compressive load on the rod. At TDC on the exhaust stroke, the piston is trying to continue upward while the crankshaft is trying to pull it back down, resulting in tension exerted on the rod. With all of this said, a quality forged connecting rod is expected to handle in the range of 1,000 hp. For big power builds, select high-quality forged or billet rods that have been properly designed, machined, stress relieved, and inspected for anticipated performance applications by any of the established aftermarket rod makers. If you plan to exceed 400 hp, it’s best to shy away from powdered metal OEM rods.
Manley
Manley’s H-beam and I-beam construction comes in lengths of 6.100 and 6.125 inches. In addition, it offers longer rods for tall deck blocks, including 6.300 inches for RHS tall deck blocks, 6.350 inches for World Warhawk tall deck blocks, and 6.460 inches for GM LSX tall deck blocks. While either H-beam or I-beam forged rods offer far superior strength as opposed to pressure-cast powdered metal rods, H-beam rods are generally considered a bit stronger than I-beam designs.
MGP Connecting Rods
MGP specializes in aluminum rods, custom made to order, for horsepower ranges from 600 to 1,100 hp. Aluminum rods, once considered only for extreme horsepower builds, are becoming more popular for those building upward of 240 to 300 hp per cylinder. Aluminum rods offer a few advantages, including lighter weight for higher revs and the ability to reduce bearing wear, as aluminum tends to absorb shock more than steel rods. However, aluminum rods are larger than steel rods in terms of material thickness, so more attention needs to be paid to rod-to-block and rod-to-cam clearance. Also, aluminum rod length tends to grow more under stress, so an additional .010 inch or so should be added at the piston-to-head clearance. The downside to aluminum rods is expense; aluminum rods are more costly than steel rods.
Oliver
Oliver offers rods in both standard 2.100-inch journals and 2.000-inch journals, at a 6.125-inch length. In addition, its Speedway Series offers rods for blown and turbo applications of up to 2,000 hp.
Scat Enterprises
Scat offers a variety of performance rods in both H-beam and I-beam designs, machined from 4340 steel, including the Premium Pro, Premium Pro Sport, and Ultra Lite Series. A variety of lengths are available, as well as choices of wrist pin diameters of .927 and .945 inch. Scat’s stroker rods provide low-profile big-end shoulders for increased clearance.
Venolia
Venolia specializes in custom-order aluminum rods for all-out racing applications. Bear in mind that aluminum rods are thicker than steel rods, so extra attention must be paid when checking big-end clearances to the block pan rail, cylinder bottoms, and other components.
High-Performance Crankshafts
Crankshaft are available in cast, forged, and billet materials. Cast iron or steel is the most economical, as molten metal is poured into a mold, with subsequent machining, heat treating, and stress relieving and nitriding for hardness. Cast cranks are generally heavier and somewhat more brittle compared to a forging, being more prone to fractures under high-stress conditions. However, for the average factory stock street car, with the engine built to a moderate power level, a cast crank will get the job done. It’s difficult to give a horsepower rating because many variables enter the picture, such as quality of the material, balancing, assembly technique, and level of abuse, to name a few. If I were to assign a number, a quality cast crank should be acceptable up to about the 500-hp range. A quality aftermarket cast crank runs in the range of about $250 to $450. Today’s cast cranks offered by leading manufacturers provide far higher quality and greater durability than in decades prior.
For high-horsepower performance, forged cranks are much stronger and will better withstand the forces applied by the rod and piston. Forged cranks are generally made using one of two metal makeups: 4130 or 4340. Both feature a percentage of molybdenum for added strength, with 4130 having about 20 percent moly and 4340 about 25 percent moly. Both nickel and carbon are part of the mix, to add hardness and grain uniformity. The 4340 cranks feature a greater carbon and nickel content. The 4130 cranks are a bit lighter, while 4340 cranks offer the highest strength. This is a very brief explanation of the material mix numbers, but the point is that 4340 cranks are more suited to high-performance applications. Expect to pay in the neighborhood of $700 to $1,000 for a quality forged crank.
Billet cranks start as high-density bar-stock forgings with a very uniform grain pattern, 100-percent machined to final shape and finish. Top makers of billet cranks choose the highest-grade billet bar stock, taking care to avoid any material that may contain inclusions that can result from hammer forging, where atmospheric particles might be introduced. They go to lengthy procedures to ensure that tensile strength is optimized. Not surprisingly, billet cranks are more costly to manufacture, and they can run $2,000 to $3,000. Billet cranks are commonly used in NASCAR and 10,000-hp Top Fuel engines.
Why the disparity in prices between forged cranks and billet? Producing forged crankshafts requires designing and making a two-piece mold, which is a hefty investment. However, forged cranks for common applications are made in quantity, keeping the price affordable. A billet crank requires no mold and the CNC-machining process allows the maker to machine any profile, so you might first think that it would be less expensive, but this still requires buying much more expensive billet bar stock, and CNC-machine hours to produce “one off” cranks. If you can afford a high-dollar billet crank, there’s no downside other than the higher cost. For most of us, a quality forged crank will fill the bill and should handle upward of 2,000 hp.
Some forged cranks are made using a twist or nontwist method. A twisted crank is made with rod throws inline in a single plane. After the initial forging process, specific main journals are then heated to a malleable state. The crank is then twisted to place the rod journals into their required offset positions. This causes the grain of the steel to be interrupted and nonuniform, potentially decreasing crank strength. All the aftermarket crank makers that I’m aware of use a nontwist approach. A nontwist forging is created by forging the crankshaft in two planes from the very start, placing the rod pins in the proper angles, requiring only finish machining, stress relieving, and heat treating.
Manufacturers of highperformance crankshafts offer several enhancements that improve durability and the ability to rev faster and at higher RPM while reducing weight. Examples include gun-drilling, where the main centerline is drilled to remove mass. Reducing weight at the centerline of rotation won’t make the crank rev higher, but this is a step that reduces crank weight, and any weight reduction to the vehicle is beneficial. Rod journals are drilled through to reduce both overall and rotational weight. Fillets, the corners of the bearing journals that meet the counterweights, are generously radiused instead of being square cut, which enhances strength by removing stress risers. A feature that may be standard or optional, depending on the crank, is aero-profiling the counterweights, where the trailing faces of the counterweights are tapered much like the trailing edge of an airplane wing. This reduces parasitic oil weight as the crank spins, allowing oil to leave the counterweight surfaces quicker, reducing drag. Another enhancement, not really necessary for most street-strip performance builds, includes removing mass from the counterweights in order to produce a lightweight crankshaft by CNC-carving or skeletonizing the counterweights.
Bryant Racing
Bryant specializes in custom-ordered cranks machined from billet steel, targeted at pro-level competition use. Any sensible stroke, journal diameter, or custom feature is available. Its Ultralight Package offers counterweight grooving, lightening holes, scalloped flange, etc., to produce the lightest crank that will still handle high loads. It also offers in-house REM Isotropic super finish, which produces a low Ra finish for enhanced friction reduction.
Callies
Callies offers an extremely wide selection of cranks, including Ultra Billet, Magnum, Magnum XL, Stock Eliminator, and Dragonslayer models. Designs range from stock configuration to super-exotic scalloped and lightened versions for street to street/race to all-out competition.
Eagle Specialty Products
Eagle’s line of 4340 forged-steel cranks for LS applications includes stroke choices of 3.6220, 4.000, 4.125, 4.250, and 4.3750 inches, handling horsepower from 1,000 to 1,500. All are available with either 24- or 58-tooth reluctors.
K1 Technologies
All cranks are forged steel with 2.650-inch main and 2.100-inch rod journals. Available strokes (each with either 24- or 58-tooth reluctors) include 3.622, 3.900, 4.000, 4.100, 4.125, and 4.250 inches.
Kings Crankshaft
Kings is another firm that specializes in custom billet crankshafts, made to order. Starting with high-density forged-billet blanks, the crankshafts are then entirely precision CNC-machined.
Lunati
All Lunati cranks are made of 4340 nontwist forged steel. Three different lines of cranks are available: the Voodoo Series, Signature Series, and Signature Series Blower. All feature 2.559-inch main and 2.100-inch rod journals.
The Voodoo Series’ (non-LS7 type) available strokes include 4.000 or 4.100 inches.
The Signature Series is Lunati’s premium performance line, with rated capability of handling more than 1,500 hp. Features include gun-drilled mains, micro-polished journals, windage-reducing contoured wing counterweights, and plasma nitriding. Strokes available in the non-LS7 type include 3.622, 4.000, 4.125, 4.250, 4.500, and 4.600 inches. The LS7 long-nose line offers strokes of 4.000, 4.125, 4.500, and 4.600 inches.
The Signature Series Blower line, intended for high-pressure forced induction, includes dual keyways, larger-diameter nose bolt threads, and larger-diameter flexplate flange threads. The Blower line offers the non-LS7 type in strokes of 4.000, 4.250, 4.425, 4.500, and 4.600 inches. The Blower long-nose LS7 type is available with strokes of 4.000, 4.125, 4.250, 4.500, and 4.600 inches.
Manley Performance Products
Manley offers three lines of cranks: Lightweight LS non-LS7, Lightweight LS7, and Super Lightweight. All are machined from 4340 forgings, all with 2.559-inch main and 2.100-inch rod journals. Note: Manley cranks are not intended for highly boosted Roots-style cog belt supercharger applications.
The Lightweight LS (standard snout length) is offered in strokes of 3.622, 4.000, and 4.100 inches, available with either 24- or 58-tooth reluctors. The Lightweight LS7 type (long nose) is available in strokes of 4.000 or 4.100 inches, with a 58-tooth reluctor only. The Super Lightweight line is available in a 4.000-inch stroke with 24- or 58-tooth reluctor. Features include nitriding, stress relief, gun-drilled mains, lightened rod journals, and fully profiled counterweights.
Scat Enterprises
Scat cranks are made of 4340 forged steel that is heat treated, shot-peened, and nitrided for added hardness. All LS cranks feature 2.100-inch rod journals, lightened rod throws, gun-drilled mains, large radius on all journal fillets, and dual linear post keyways for keyed dampers. Available strokes include 3.622, 4.000, 4.125, and 4.250 inches.
Winberg Crankshafts
Winberg cranks are intended for upper-level professional racing applications, and they are primarily custom ordered for stroke and journal size. All are fully counterbalanced and are available with or without reluctors. LS1-style cranks (applicable to all blocks except LS7 and LS9) are offered in strokes of 3.250, 3.400, 3.500, 3.625, 3.750, and 4.000 inches, with rod journals of 2.000, 2.100, or 1.888 inches. The long-snout LS7/LS9 cranks are offered in 3.400-inch or 4.000-inch strokes. All feature a main diameter of 2.559 inches.
