K1 is flush with LS stroker crankshafts to take your block from boring to big-inch.
Ready to feel old? The LS engine turned 21 this year. If it were human, it would have a high-school diploma and could legally down a six-pack of beer. After two decades of LS swaps, builds, records, and race wins, it's as popular as ever, and there more of cores than ever to go around.
If you've picked up an LS core for your project, there's a good chance it has considerable miles on it. A bore, hone, and hot tank almost always work into the build plan, but what about the crank? The stock LS crankshaft is a stout and admirable piece, but one of the many strong points of the LS architecture is its taller deck height (over the gen I small block) and the ability to stroke it to torquier cubic inches.
That's where K1's line of LS stroker crankshafts come in. Currently available in 4.00in, 4.125in, and 4.250in, strokes, these longer arms can add invaluable displacement to your build. Better yet, they are also available as rotating kits prepackaged with the correct rods and pistons for an easy inch increase.
A Sum Greater Than The Parts
K1 built their reputation around crankshafts and rods that deliver quality at an affordable price, offering value that your average imported parts canâ€™t match. However, they've teamed up with Wiseco pistons to provide complete rotating assembly kits that pair professionally-matched components into a single part number to make ordering simple.
â€œWe currently offer Chevy LS applications as an off the shelf rotating assemblies,â€ K1â€™s Nick DiBlasi explains. â€œHowever, many of our customers make their own combinations with our pistons, rods, and cranks daily. We found it easy for our customers to pick and choose any combination they wanted and we could suit their needs.â€
Itâ€™s no surprise that the LS engine family would be the first target on K1â€™s radar for complete kits; factory blocks are so ubiquitous and cheap that theyâ€™ve become the hands-down favorite for racers and hot rodders looking for a solid foundation for a high-horsepower build. Though the stock LS components can definitely take a beating, upgrading the internals is a sure-fire way to create a durable, powerful race or high performance street engine.
Crank it Up
K1â€™s LS rotating assemblies start with a high-quality crankshaft, with a number of options. Both 58 and 24 tooth reluctors are available, and customers have a wide selection of crank throws from stock to stroker. Per DiBlasi, â€œThe K1 LS cranks are all forged 4340 steel and are designed for the latest demands of our customers. We offer strokes from factory 3.622 all the way up to 4.250, in 3.622, 3.900, 4.000, 4.100, 4.125, and 4.250 throws.â€
A nitrided finish improves crank strength and bearing life, and the large-radius fillets remove potential areas of stress concentration and potential failure. K1 employs a straight hole oiling system for superior bearing lubrication, and tolerances are held to plus or minus one ten thousandth of an inch.
The second ingredient in the successful recipe is a robust connecting rod, and K1 has that covered as well. â€œWe offer our K1 H-beam 4340 forged rods with our kits,â€ DiBlasi explains. â€œThey are designed specifically to be matched with our crankshafts and clear all the stroker applications. They feature ARP2000 bolts and have seen over 1,500 horsepower on many of our customersâ€™ race cars.â€
Many racers will debate the relative benefits of an H-beam versus an I-beam design in terms of ultimate strength, but for applications where shaving grams isnâ€™t absolutely critical, the H-beam delivers additional rigidity and better load distribution than a comparable I-beam connecting rod, and makes perfect sense for K1â€™s rotating assembly kits. Dual reinforced ribs add strength on the big end, while radiused sides maximize clearance. A shot peened finish is the finishing touch, placing the outer surface in compression and removing any potential locations for stress riser formation.
Slugging it Out
When it comes to pistons, Wiseco offers a wide selection, no matter what bore or compression ratio youâ€™re shooting for. Per DiBlasi, â€œOur main rotating assemblies come packaged with Wiseco pistons. We offer various popular compression ratios based off the combinations we know work best.â€ Depending on combustion chamber volume, the shelf stock LS rotating assemblies range from 9.3:1 to 13.0:1, suitable for boosted or naturally aspirated builds.
Wisecoâ€™s Professional Series forged pistons also utilize their proprietary ArmorGlide skirt coating that reduces friction, increases horsepower, and improves wear resistance. â€œIf you are looking for a compression ratio that we do not offer [in a stocking part number], we can gladly build a rotating assembly with the same components and another piston combination that we offer,â€ DiBlasi adds.
When you order up a rotating assembly from K1, youâ€™re getting all the other matched components you need to round out the engine internals as well. â€œThey come with pistons, pins, locks, and rings,â€ DiBlasi explains. The goal is to provide everything you need under a single part number, so that you can order with confidence, knowing that there wonâ€™t be any bits and pieces that you need to figure out before you start putting everything together. â€œAll of our kits come with rod and main bearings,â€ he adds.
â€œOur kits are designed to go together and have been tested on our in-house dyno,â€ DiBlasi says. â€œWe have an in-house engine dyno just for LS-based engine testing. Everything was designed to work together. We take the work out of ordering parts from different places, and do the testing for you. Creating rotating assembly kits for the LS family was simply a no-brainer."
An intense look at crankshaft stroke and its affect on mean piston speed, inertia, and controlling the massive, destructive forces at work inside an engine.Engine builders have long calculated the mean piston speed of their engines to help identify a possible power loss and risky RPM limits. This math exercise has been especially important when increasing total displacement with a stroker crankshaft, because the mean piston speed will increase when compared to the standard stroke running at the same RPM.
But what if there was another engine dynamic that could give builders a better insight into the durability of the reciprocating assembly?The video above shows two engines, one with a short stroke crankshaft, and the other with a considerably longer stroke. Note that both pistons reach top dead center and bottom dead center at the same time, but the piston in the longer stroke engine (left) has to move significantly faster.
â€œRather than focus on mean piston speed, look at the effect of inertia force on the piston,â€ suggests Dave Fussner, head of research and development at K1 Technologies.
Letâ€™s first review the definition of mean piston speed, also called the average piston speed. Itâ€™s the effective distance a piston travels in a given unit of time, and itâ€™s usually expressed in feet per minute (fpm) for comparison purposes. The standard mathematical equation is rather basic:
Mean Piston Speed (fpm)=(Stroke x 2 x RPM)/12
Thereâ€™s a simpler formula, but more on the math later. A pistonâ€™s velocity constantly changes as it moves from top dead center (TDC) to bottom dead center (BDC) and back to TDC during one revolution of the crankshaft. At TDC and BDC, the speed is 0 fpm, and at some point during both the downstroke and upstroke it will accelerate to a maximum velocity before decelerating and returning to 0 fpm.
There are formulas to calculate the piston speed at every degree of crankshaft rotation, but thatâ€™s usually much more information than needed by most engine builders. Traditionally they look at the average or mean piston speed during the crank rotation, and they possibly will calculate the maximum piston speed.
The mean piston speed takes the total distance the piston travels during one complete crankshaft revolution and multiplies that by the engine RPM. Piston speed obviously increases as the RPM increase, and piston speed also increases as the stroke increases. Letâ€™s look at a quick example.
A big-block Chevy with a 4.000-inch-stroke crankshaft running at 6,500 rpm has mean piston speed of 4,333 fpm. Letâ€™s review the formula again used to calculate this result. Multiply the stroke times 2 and then multiply that figure by the RPM. That will give you the total number inches the piston traveled in one minute. In this case, the formula is 4 (stroke) x 2 x 6,500 (RPM), which equals 52,000 inches. To read this in feet per minute, divide by 12. Hereâ€™s the complete formula:
(4 x 2 x 6,500)/12=4,333 fpm
You can simplify the formula with a little math trick. Divide the numerator and denominator in this equation by 2, and youâ€™ll get the same answer. In other words, multiply the stroke by the RPM, then divide by 6.
(4 x 6,500)/6=4,333 fpm
With this simpler formula, weâ€™ll calculate the mean piston speed with the stroke increased to 4.500 inch.
(4.5 x 6,500)/6=4,875 fpm
As you can see, the mean piston speed increased nearly 13 percent even though the RPM didnâ€™t change.
Again, this is the average speed of the piston over the entire stroke. To calculate the maximum speed a piston reaches during the stroke requires a bit more calculus as well as the connecting rod length and the rod angularity respective to crankshaft position. There are online calculators that will compute the exact piston speed at any given crankshaft rotation, but hereâ€™s a basic formula that engine builders have often used that doesnâ€™t require rod length:
Maximum Piston Speed (fpm)=((Stroke x Ï€)/12)x RPM
Letâ€™s calculate the maximum piston speed for our stroker BBC:
((4.5 x 3.1416)/12)x 6,500=7,658 fpm
By converting feet per minute to miles per hour (1 fpm = 0.011364 mph), this piston goes from 0 to 87 mph in about two inches, then and back to zero within the remaining space of a 4.5-inch deep cylinder. Now consider that a BBC piston weighs about 1.3 pounds, and you can get an idea of the tremendous forces placed on the crankshaft, connecting rod and wrist pinâ€”which is why Fussner suggests looking at the inertia force.
â€œInertia is the property of matter that causes it to resist any change in its motion,â€ explains Fussner. â€œThis principle of physics is especially important in the design of pistons for high-performance applications.â€
The force of inertia is a function of mass times acceleration, and the magnitude of these forces increases as the square of the engine speed. In other words, if you double the engine speed from 3,000 to 6,000 rpm, the forces acting on the piston donâ€™t doubleâ€”they quadruple.
â€œOnce started on its way up the cylinder, the piston with its related components attempt to keep going,â€ reminds Fussner. â€œIts motion is arrested and immediately reversed only by the action of the connecting rod and the momentum of the crankshaft.â€
Due to rod angularityâ€”which is affected by connecting rod length and engine strokeâ€”the piston doesnâ€™t reach its maximum upward or downward velocity until about 76 degrees before and after TDC with the exact positions depending on the rod-length-to-stroke ratio,â€ says Fussner.
â€œThis means the piston has about 152 degrees of crank rotation to get from maximum speed down to zero and back to maximum speed during the upper half of the stroke. And then about 208 degrees to go through the same sequence during the lower half of the stroke. The upward inertia force is therefore greater than the downward inertia force.â€
If you donâ€™t consider the connecting rod, thereâ€™s a formula for calculating the primary inertia force:
0.0000142 x Piston Weight (lb) x RPM2 x Stroke (in) = Inertia Force
The piston weight includes the rings, pin and retainers. Letâ€™s look at a simple example of a single-cylinder engine with a 3.000-inch stroke (same as a 283ci and 302ci Chevy small-block) and a 1.000-pound (453.5 grams) piston assembly running at 6,000 rpm:
0.0000142 x 1 x 6,000 x 6,000 x 3 = 1,534 lbs
With some additional math using the rod length and stroke, a correction factor can be obtained to improve the accuracy of the inertia force results.
Crank RadiusÃ·Rod Lenth
â€œBecause of the effect of the connecting rod, the force requi