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Whether you're racing or looking for increased performance out on the trail, there are a plethora of performance upgrades to consider to increase the power of your machine. Piston manufacturers like JE Pistons offer high compression piston options for many applications, but there are important merits and drawbacks you should consider when deciding if a high compression piston is right for your application. To better understand, we’ll take a look at what increasing compression ratio does, what effects this has on the engine, detail how high compression pistons are made, and provide a high-level overview of which applications may benefit from utilizing a high compression piston. Bumping up the compression in your motor should be an informed decision. It's important to first understand what effects high-compression has, the anatomy of a high-comp piston, and what applications typically benefit most. Let’s start with a quick review of what the compression ratio is, then we’ll get into how it affects performance. The compression ratio compares the volume above the piston at bottom dead center (BDC) to the volume above the piston at top dead center (TDC). Shown below is the mathematical equation that defines compression ratio: The swept volume is the volume that the piston displaces as it moves through its stroke. The clearance volume is the volume of the combustion chamber when the piston is at top dead center (TDC). There are multiple different dimensions to take into account when calculating clearance volume, but for the sake of keeping this introductory, this is the formula as an overview. When alterations to the compression ratio are made, the clearance volume is reduced, resulting in a higher ratio. Reductions in clearance volume are typically achieved by modifying the geometry of the piston crown so that it occupies more combustion chamber space. Swept volume is the volume displaced as the piston moves through the stroke, and clearance volume is the volume of the combustion chamber with the piston at top dead center. How does an increased compression ratio affect engine performance? To understand how increasing the compression ratio affects performance, we have to start with understanding what happens to the fuel/air mixture on the compression stroke. During the compression stroke, the fuel/air mixture is compressed, and due to thermodynamic laws, the compressed mixture increases in temperature and pressure. Comparatively, increasing the compression ratio over that of a stock ratio, the fuel/air mixture is compressed more, resulting in increased temperature and pressure before the combustion event. The resulting power that can be extracted from the combustion event is heavily dependent on the temperature and pressure of the fuel/air mixture prior to combustion. The temperature and pressure of the mixture before combustion influences the peak cylinder pressure during combustion, as well as the peak in-cylinder temperature. For thermodynamic reasons, increases in peak cylinder pressure and temperature during combustion will result in increased mechanical efficiency, the extraction of more work, and increased power during the power stroke. In summary, the more the fuel/air mixture can be compressed before combustion, the more energy can be extracted from it. Higher compression allows for a larger amount of fuel/air mixture to be successfully combusted, ultimately resulting in more power produced during the power stroke. However, there are limits to how much the mixture can be compressed prior to combustion. If the temperature of the mixture increases too much before the firing of the spark plug, the mixture can auto ignite, which is often referred to as pre-ignition. Another detrimental combustion condition that can also occur is called detonation. Detonation occurs when end gases spontaneously ignite after the spark plug fires. Both conditions put severe mechanical stress on the engine because cylinder pressures far exceed what the engine was designed for, which can damage top end components and negatively affect performance. Detonation and pre-ignition can spike cylinder pressure and temperature, causing damage. Common signs of these conditions include pitting on the piston crown. Now that there is an understanding of what changes occur during the combustion event to deliver increased power, we can look at what other effects these changes have on the engine. Since cylinder pressure is increased, more stress is put on the engine. The amount of additional stress that is introduced is largely dependent on the overall engine setup. Since combustion temperatures increase with increased compression ratio, the engine must also dissipate more heat. If not adequately managed, increased temperatures can reduce the lifespan of top-end components. JE's EN plating is a surface treatment that can protect the piston crown and ring grooves from potential damage caused by high cylinder pressure and temperature. EN can be an asset for longevity in a high-compression race build. Often, additional modifications can be made to help mitigate the side effects of increasing the compression ratio. To help reduce the risk of pre-ignition and detonation, using a fuel with a higher octane rating can be advantageous. Altering the combustion event by increasing the amount of fuel (richening the mixture) and changing the ignition timing can also help. Cooling system improvement can be an effective way to combat the additional heat generated by the combustion event. Selecting larger or more efficient radiators, oil coolers, and water pumps are all options that can be explored. Equipping the engine with a high-performance clutch can help reduce clutch slip and wear which can occur due to the increased power. High-level race team machines are great examples of additional modifications made to compensate for increased stress race engines encounter. Mods include things like larger radiators, race fuel, custom mapping, and performance clutch components. Let’s take a quick look at what considerations are made when designing a high compression piston. Typically, high compression pistons are made by adding dome volume to the piston crown, which reduces the clearance volume at TDC. In some cases, this is difficult to do depending on the combustion chamber shape, size of the valves, or the amount of valve lift. When designing the dome, it is essential to opt for smooth dome designs. Smooth domes as opposed to more aggressively ridged designs are preferred because the latter can result in hot spots on the piston crown, which can lead to pre-ignition. Another common design option is to increase the compression distance, which is the distance from the center of the wrist pin bore to the crown of the piston. In this approach, the squish clearance, which is the clearance between the piston and head, is reduced. Higher compression is commonly achieved by increasing dome volume while retaining smooth characteristics, as pictured here with raised features and deep valve pockets. Compression height can also be increased, which increases the distance between the center of the pin bore and the crown of the piston. A high-level overview of which applications can benefit from increased compression ratio can be helpful when assessing whether a high-compression upgrade is a good choice for your machine. Since increasing the compression ratio increases power and heat output, applications that benefit from the additional power and can cope with additional heat realize the most significant performance gains. Contrarily, applications where the bike is ridden at low speed, in tight conditions, or with lots of clutch use can be negatively impacted by incorporating a high compression piston. Keep in mind these statements are generalizations, and every engine responds differently to increased compression ratios. Below are lists of applications that may benefit from increasing the compression ratio as well as applications where increased compression may negatively influence performance. Applications that may benefit from utilizing a high compression piston: Motocross Supermoto Drag racing Road racing Ice racing Flat track Desert racing Motocross and less technical off-road racing are two of multiple forms of racing in which high-compression pistons can benefit performance due to higher speeds and better air flow to keep the engine cool. Peick photo by Brown Dog Wilson. Applications that may be negatively affected by utilizing a high compression piston: Technical off-road/woods riding Trials Other low speed/cooling applications Lower speed racing and riding may not benefit as much from a high-compression piston, as heat in the engine will build up quicker due to lessened cooling ability. Fortunately, if you’re considering increasing your engine’s compression ratio by utilizing a high compression piston, many aftermarket designs have been tested and optimized for specific engines and fuel octane ratings. For example, JE Pistons offers pistons at incrementally increased compression ratios so that you can incorporate a setup that works best for you. For example, high-compression pistons from JE for off-road bikes and ATVs are commonly available in 0.5 compression ratio increases. Assume an engines stock compression ratio is 13.0:1, there will most likely be options of 13.5:1 and 14.0:1, so that you can make an informed decision on how much compression will benefit you based on your machine and type of riding. From left to right are 13.0:1, 13.5:1, and 14.0:1 compression ratio pistons, all for a YZ250F. Notice the differences in piston dome volume and design. If performance is sufficient at an engine’s stock compression ratio, there are still improvements in efficiency and durability that can be made with a forged piston. Forged pistons have a better aligned alloy grain flow than cast pistons, creating a stronger part more resistant to the stresses of engine operation. In addition to forged material, improvements can be made on piston skirt style design to increase strength over stock designs, such as with JE’s FSR designs. JE also commonly addresses dome design on stock compression pistons, employing smoothness across valve reliefs edges and other crown features to improve flame travel, decrease hot spots, and ultimately increase the engine’s efficiency. Even if stock compression is better for your application; forged construction, stronger skirt designs, and more efficient crown designs can still provide improved performance and durability. If it’s time for a new piston but you’re still not sure what compression ratio to go with, give the folks at JE a call for professional advice on your specific application.
Different machines, types of riding, and skill levels may benefit from different clutch setups. So how do you decide which clutch is right for you? Here, we break down each of Rekluse's clutch offerings to help you make an informed decision. While riding a motorcycle may seem elementary to an experienced individual, it’s not the act of riding that’s so impressive as how a motorcycle works. Very few people take to the time to think about all of the minute steps required for a bike to even start, let alone be ridden. Of course, there’s the piston pumping up and down, fuel igniting in the combustion chamber, and the crankshaft turning energy into rotary motion. One of the most overlooked components of an engine is the clutch system. In fact, it’s generally considered an afterthought; that is, until it stops functioning properly. Never overlook the importance of a properly functioning clutch. Motorcycle enthusiasts may view the engine’s clutch as a small piece of a large puzzle, unnecessary to worry about until new clutch plates are required. However, the clutch can actually be a huge performance advantage. Rekluse, an Idaho-based company that has been making their own line of clutch systems for 17 years, knows this all too well. Their first centrifugal automatic clutch (known as the Z-Start), put them on the map. Top off-road racers across various disciplines have raced, and won, with the Rekluse auto clutch. As an aftermarket company, reaching the pinnacle of the sport can’t be accomplished by offering an inferior product. Every component is tested to its maximum capabilities before ever being used in a race situation. Today's Rekluse clutches are the result of 17 years of development, engineering, and testing. This is an ever-evolving process that fuels Rekluse's continued development. Rekluse offers six different options across the auto and manual clutch categories for dirt bikes. Although known for their automatic clutch systems, Rekluse makes state-of-the-art manual clutch packages. Which one is right for you? Auto or manual? RadiusCX or EXP 3.0? Core Manual TorqDrive or Core Manual? Read on to find out. Understand Your Options Think about your preferences, expertise, and shortcomings as a rider. Are you a beginning motocross racer, focused on mastering throttle control and maintaining corner speed? Perhaps you’re an avid trail seeker, searching for unconquered terrain in the most hostile environments. Whatever the case, it’s important to understand that your bike’s clutch can either help or hinder your goals as a rider. Understand that you have options. Different riders will benefit from different clutch setups. Read on to understand which of the various options will be most beneficial for you. Conventional clutch systems can be easily abused, leading to premature wear and eventual failure. Constantly pulling in and releasing a clutch lever causes fatigue. Automatic clutches can help solve those problems. Is there a drawback to using an auto clutch? Some may find the technology foreign, requiring practice in order to achieve comfort. Wrap your head around the idea of coming to a stop with the bike in gear and your hand off the clutch. Fortunately, Rekluse covers the spectrum of clutch configurations. Rekluse Technology Through extensive research and development, Rekluse created three technological advancements that are shared among various clutch systems in their line. These components are a telling sign of Rekluse’s commitment to achieving clutch mastery. EXP The Houdini of clutch tech, Rekluse’s EXP disk is responsible for engaging and disengaging the clutch based on centrifugal force. When the motorcycle reaches a certain rpm, the EXP wedges slide out to expand the disk and engage the clutch. All of this is happening from engine idle to about 3,000 rpm. The point at which the clutch engages can be fine-tuned with different wedges and springs for a customized feel. The EXP disk is the key to auto clutch performance. This is the piece that automatically expands and contracts based on RPM to engage and disengage the clutch. Austin Paden, Rekluse Product Manager/Race Development, elaborates, “There was a lot of thought that went into the ramp angles during the development process, and how the wedges would ramp out while rotating. Small changes to the wedges made a big difference in how the auto clutch performed. Our goal was to make something lightweight, easy to adjust, and functional.” This graphics illustrates the simple, but innovative, process of the EXP disk and how it achieves auto clutch functionality. EXP technology is utilized on the RadiusCX, RadiusX and Core EXP 3.0 automatic clutch systems. Read more about how EXP works and find clutch systems with EXP here. TorqDrive Exactly what the name implies, TorqDrive is based on the principle that using more friction plates in a clutch pack creates increased torque capacity. Rekluse accomplished this by decreasing the thickness of their plates in order to use more plates in the same confines, while developing their own friction material for increased durability. Check out how TorqDrive increases torque capacity. Paden states, “The idea was to increase torque capacity to the system. Ultimately, the goal was to allow for more tuning options, lighter feel at the lever, and lessen clutch operating temperatures. The world of Supercross and motocross is based around a standard functioning manual clutch. The market in that segment is very competitive. We learned that other companies were using standard-based friction plates. Yet race teams were still having issues with breaking friction plates and experiencing clutch fade, which was caused by expansion. Our goal was to find a fiber compound that was durable, even when the operating temperature became extremely hot, yet be thin enough to fit more fiber plates into that same working area.” "Our goal was to find a fiber compound that was durable, even when the operating temperature became extremely hot, yet be thin enough to fit more fiber plates into that same working area." - Austin Paden, Product Manager The friction plates are made out of steel, which bucks the trend of using aluminum. When subjected to extreme heat, aluminum expands roughly twice as much as steel. Expansion leads to clutch fade. Rekluse essentially solved an age-old clutch malady through metallurgy. Additionally, the steel-based friction plates have unusually shaped friction material totally unlike a traditional square or rectangle-shape. Paden explains, “We came up with our own fiber material and design, which is based around oil flow. That material is on a steel core, which maintains its integrity, even when the engine gets really hot. As a result, you don’t get clutch fade or constantly have to adjust the clutch cable in the middle of your moto. The Rekluse TorqDrive system contains 12 friction plates in most Japanese-manufactured bikes, versus seven or eight in a OEM/stock configuration.” Additionally, the TorqDrive pack comes with steel lining clutch basket sleeves to eliminate wear and notching to the clutch basket tangs. Rekluse left no stone unturned. Rekluse developed a more durable clutch fiber compound while simultaneously improving the pad design for better cooling. The fiber material sits on a steel core, creating a complete package that drastically reduces clutch fade. TorqDrive technology can be found in the RadiusCX and RadiusX auto clutches, as well as the Core Manual TorqDrive and TorqDrive Clutch Pack manual editions. Read more about how TorqDrive works and find TorqDrive-equipped clutch systems here. Core Heat is the mortal enemy of an engine’s clutch. Rekluse confronted that problem head-on by developing their own hub, pressure plate and clutch cover. Made out of billet aluminum and designed around optimizing oil flow to lower clutch operating temperatures, Core is literally cool. Paden states, “We made the parts lighter in order to create less rotating mass. In comparison to the competition, what’s noticeable about our hubs and pressure plates are that they have very open profiles. The bottom and top of the hub have features that basically act as a dam for the oil. Oil that makes its way into the center hub is directed through the clutch plates. More flow reduces heat. The pressure plate is also open, and any oil that comes from the front side of the clutch system makes its way to the center clutch.” Rekluse Core billet inner hubs and pressure plates are designed to promote better oil flow and less rotating mass. A close inspection of an OEM/stock hub will likely reveal oil holes and features that are located in the profile where the drive plates would ride. With this design, the holes are potentially blocked, preventing oil from reaching the clutch plates. Rekluse found a solution. Paden explains, “The Rekluse-designed hub has the oil holes and features on the ribs themselves. There are features in the drive plates, which act like pockets, so the oil is able to flow to the clutch plates without restriction.” Taking it a step further, Rekluse created their own clutch cover that allows for roughly 50cc more oil capacity. More oil equals decreased operating temperature. Rekluse billet hubs have oil flow features directly on the ribs, adding another measure to clutch plate oiling. Also, Rekluse billet clutch covers allow for additional oil capacity to keep things cooler. Core technology is utilized in RadiusCX and Core EXP 3.0 auto clutches, as well as Core Manual TorqDrive and Core Manual clutches. Read more about Core technology and find Core-equipped clutch systems here. Automatic: What are your Options? Rekluse offers three automatic clutch options – RadiusCX, RadiusX, and Core EXP 3.0. RadiusCX is the Taj Mahal of automatic clutch systems, featuring a plethora of Rekluse’s latest technologies. It contains the best features, as far as cooling and auto clutch performance. If you are a clutch abuser, the RadiusCX is for you. Like the other auto clutch options, the rider can use the clutch lever for manual operation. Given that it’s full of benefits, this is also the most expensive auto clutch in Rekluse’s line ($1,019). The RadiusCX is the ultimate clutch package for riders desiring the auto clutch. It includes the Core billet components, TorqDrive technology, the EXP 3.0 disk, and the billet slave cylinder for DDS models (shown here). Find RadiusCX for your ride here. RadiusX is the little brother to the RadiusCX. Featuring EXP and TorqDrive technology, the system comes with the EXP disk and clutch pack, as well as the clutch basket sleeves. It does not come equipped with the Core billet components, and as such, is priced at $629. The RadiusX features EXP and TorqDrive to deliver a great auto clutch experience, it just does not include the Core billet components to keep the price point lower. Find RadiusX for your ride here. Core EXP 3.0 ($919) utilizes the EXP centrifugal disk, meaning that you can come to a complete stop in gear with clutch out and not stall the bike. The package also includes the Core billet parts. OEM/stock clutch plates are required with the Core EXP 3.0. The Core EXP 3.0 includes the EXP disk and all the Core billet components, but utilizes stock clutch plates. Find Core EXP 3.0 for your ride here. Manual: What Are Your Options? Rekluse also offers three manual clutch options – Core Manual TorqDrive, Core Manual, and TorqDrive Clutch Pack. Core Manual TorqDrive ($949) was designed for serious racers, used at the Supercross level on down to the amateur ranks. It has the most adjustments as far as tunability, and outstanding durability. The kit comes with Core and TorqDrive technology. Find Core Manual TorqDrive for your machine here. The Core Manual TorqDrive kit inludes Core billet components and TorqDrive technology. The power delivery improvement and added durability is nothing short of impressive. Core Manual is essentially a billet replacement for the stock hub and pressure plate. Some riders may prefer the feel of riding with OEM/stock friction plates. If that statement explains you, then the Core Manual is your best option. It is priced at $519. Find Core Manual for your machine here. If you want the durability and cooling characteristics of the Core billet components but prefer the feeling of stock clutch plates, the Core Manual is your clutch. The TorqDrive Clutch Pack takes the clutch pack used in the Core Manual TorqDrive and puts it into a stock hub and pressure plate. It’s very affordable, and a good alternative for racers on a tight budget. At $349, it doesn’t break the bank. Find TorqDrive Clutch Pack for your machine here. The TorqDrive clutch pack gives you the advantages of increased torque capacity without the added cost of billet components. The most affordable way to get all the holeshots. What the Professionals Run Rekluse’s list of sponsored riders reads like a who’s who in all of the major forms of two-wheeled off-road motorcycle racing series. In fact, Rekluse relies on some of the world’s best athletes for product development and durability. Given that Rekluse produces a variety of clutch applications, it makes sense that their fleet of sponsored riders have their particular favorites. The 2018 Monster Energy Supercross Champion, Jason Anderson, along with the rest of the Rockstar Husqvarna factory team, prefers the Core Manual system, which they pair with OEM/stock fiber plates. Dean Wilson opts for the TorqDrive clutch pack, as it easily drops into a stock clutch system. The Star Racing Yamaha team has been using the full Core Manual TorqDrive kit for roughly five years. In that span, the 250 program has won championships with Cooper Webb and Aaron Plessinger. Rekluse products go through multiple stages of testing and development, from in-house prototypes to detailed refinements with elite race teams. Dubbed “Mr. Versatility” by Racer X Illustrated, Ryan Sipes has competed in a bevy of different off-road disciplines over the past few years. From ISDE to GNCC, Sprint Enduro and event Flat Track, Ryan’s clutch of choice is the RadiusCX. Another GNCC racer, Ricky Russell, has used the RadiusCX system for the past year and a half. It makes sense, given that GNCC races are gruelingly long at three hours, where hand fatigue and engine stalling can be major issues. Paden explains that Endurocross riders tend to bounce back and forth between auto and manual clutch options. “Auto clutches were incredibly popular for several years in Endurocross, and then racers started gravitating to manual clutches. Right now, we’re in this state where guys are going back to the auto systems. It’s one of those scenarios where if one guy who is winning goes auto, the rest follow.” Given that a motorcycle clutch is a beneficial aftermarket modification, it is a change that is quickly picked up and copied by the competition. Believe it or not, there are some riders who prefer to race Supercross with an automatic clutch. Paden explains, “I have done back-to-back testing with top privateers in Supercross, and most post faster lap times with an auto clutch. They couldn’t believe it. That’s because an auto clutch makes the bike's power feel smoother.” Smooth doesn’t feel fast to most riders, but the stopwatch doesn’t lie. Paden believes that more riders will start preferring automatic clutches in Supercross over time. It’s not a crazy theory, given that roll speed is an important part of clearing jumps and being successful in Supercross. While an auto clutch may not 'feel' as fast to some Supercross riders, many of those that have tested it have posted faster lap times. Could we see a migration to auto clutches in Supercross? If you’re still unsure of which Rekluse clutch to install in your motorcycle, give the clutch experts a call at 208-426-0659, or browse the Rekluse website at www.rekluse.com.