How we Developed our Best KTM 350 and 450 Four-Stroke Piston Kits Yet
As KTM has stepped up the standards in OEM engine components over recent years, Wiseco went back to the R&D department to fine-tune their four-stroke KTM pistons for improved performance and longevity characteristics over KTM’s OEM pistons. See what went into this development here.
There is no question KTM has been one of the front runners in the dirt bike industry. They have routinely cranked out technological and engineering advancements consistently every year. In the last several years, KTM has added power to its engines while reducing weight. In addition, they have extracted weight from their chassis and improved their bikes’ handling through geometry and suspension refinements. These are impressive feats. However, perhaps even more impressive is how one aftermarket company, Wiseco, keeps up and sets the bar even higher.
Wiseco has been in the piston business for over 80 years. They were in lockstep with the industry, deploying their expertise, in the early 2000s when the transition to four-stroke dirt bikes was in its infancy. Today, Wiseco continues finding innovative ways to maintain pace with OEMs like KTM and improve upon OEM designs. Wiseco’s specialty is providing customers with products that offer more performance and durability than the OEM equivalent. One of Wiseco’s latest developments is a new piston for KTM, GasGas, and Husqvarna 350 and 450cc dirt bikes. How Wiseco designed and developed this new piston and brought it to market is a fascinating feat of engineering.
Why Design a New KTM Four-Stroke Piston?
Wiseco has always considered itself a leader in piston technology and is relentlessly looking at ways to improve OEM pistons, or even their own. When deciding to design a new piston for the KTM engine, Wiseco representative Scott Highland said, “We saw an opportunity to incorporate new features into the piston design that our old design didn’t have. We’re striving to be best in class for the Austrian engine platforms since multiple models unitize common engine components, and we want to lead performance across these platforms. We studied the competition’s offering and evaluated used pistons to identify areas of improvement. We identified a series of small improvements we wanted to implement. These small but essential features ultimately increase strength and reduce weight in the new piston, improve frictional loss, improve ring seal and ultimately, long-term durability.” Anytime you can take weight out of the piston while maintaining or improving its strength is a huge deal and worth pursuing!
What Does Developing and Validating a New Piston Entail?
Once the Wiseco team kicks off the program, they start development by reviewing and scrutinizing their past development program (if they are updating a product) and the OEM version of the piston. The goal is to learn as much as possible about the existing piston because it provides the basis to start and iterate.
When reviewing the OEM piston, they use cutting-edge technical tools to capture every detail. Both new and used pistons are inspected. For example, pistons are 3D scanned to capture their dimensions, dome geometry, and to help visualize what the piston skirt profile looks like. 3D scans are validated against measurements performed by their technicians and CMM machines to ensure they are as accurate as possible. In addition, wear patterns are studied on old pistons to assess running fit, areas of abnormal wear, and to look for blow-by.
The design progresses to engineering and the virtual environment next. Engineers and designers work together to model the piston in CAD software. At this point, changes to the piston model are made to improve its performance.
Once engineering has made their updates to the piston, they begin the validation process virtually by leveraging finite element analysis (FEA). FEA allows the engineering team to simulate how the new design will respond to the thermal and mechanical loads it will see in the engine.
The design and simulation portions of the development process are iterative in nature. The engineering team learns something new after each simulation and updates its design accordingly. The culmination of all the iterative changes is what gets turned into a physical prototype for engine testing.
Between FEA and engine testing, is the ever crucial step of prototyping the new piston design and assembling the test engine. The prototype piston is forged and machined exactly as the production units will be. This work is essential and is always done in-house by seasoned team members.
For the KTM program, Wiseco used the engine from their 2020 KTM 450 SX-F dirt bike. With baseline data from OEM configuration testing on their in-house dyno already completed, a highly experienced and meticulous technician carefully assembled the test engine with the prototype piston. The technician documented all aspects of the engine build so they could be referenced after testing was complete and the engine was torn down for evaluation. Most importantly, the test engine and new piston underwent a series of static checks to double-check and ensure the running clearances within the engine were optimal.
To kick off engine testing, the Wiseco team set up their SuperFlow water brake engine dyno. The test cell is configured to collect copious amounts of data because raw horsepower and torque aren’t the only vital determinants in deciding if a test passes or fails. Water temperature, oil temperature, and blow-by are monitored, among a handful of other parameters. When testing and developing pistons, the water and oil temperature can indicate how the piston is performing inside the engine. For example, an increase in water temperature can mean excessive piston skirt-to-cylinder wall contact or an abnormal fit.
Similarly, oil temperature can spike when the heat transfer through the piston, to the rings, and out to the liner is suboptimal. Oil temps can also skyrocket when there are issues with the piston pin bore fit or small end bushing. Measuring blow-by via crankcase pressure provides critical insight into how well the piston rings are sealing.
The Wiseco team welcomes the new piston design into the world by performing a series of increasingly punishing performance and durability tests. The tests showcase some of the worst conditions imaginable for a piston and allow it to prove it will withstand the heavy-handed abuse customers will throw at it. In the case of their new KTM piston, it tested and performed exceptionally well from the get-go.
After all the engine tests have been performed, the engineers, quality inspectors, and technicians all work together to assess the condition of the tested piston. Wiseco engineer, Ryan Nau, says, “We measure the key features before and after testing, which are the major outer diameter, piston pin hole diameter, ring grooves, and lands. Visual inspection is very critical at this point. We want the part to look like it was never run, so no scuffing or heavy wear on any of the surfaces is what we’re after. We also ensure the interaction with all mating components, including the rings, pin, and circlips, is functional and visually compatible.”
Upon reviewing the piston skirt geometry from the tested piston, Wiseco opted to make a minor refinement to the piston skirt shape and clearances and retest. Ryan elaborated on the intricacies of the subtle change and stated, “This falls into our vast experience with piston shapes and how they interact with the cylinder in a running engine. The change between the first design and the second was an adjustment to the ovality of the part. We were able to look closely at the light contact marks on the first test and make an adjustment to eliminate this contact on the second prototype. This minor change was successfully tested on the first attempt.” In piston design terms, the ovality of the piston refers to its shape circumferentially at specified heights from the top of the piston all the way down to the bottom of the skirt. Therefore, adjustments to the piston’s ovality directly affect how well it mates with the cylinder bore.
After a new piston undergoes all its testing, Wiseco reviews its performance, prepares for manufacturing, and release to the market. Wiseco sets high standards for a new product launch and compares the new pistons’ performance with well-developed internal standards. Once all the criteria have been met, the piston moves on to production.
Once a new piston design is validated and approved, it moves to Wiseco’s 100% USA production.
What About Real World Testing?
Successful engineering firms know that engine dyno and real-world performance don’t always coincide. Nor does dyno testing always equate to a successful product, so real-world testing has to be part of the development program. Wiseco approaches real-world testing very seriously and equips its sponsored teams and riders with new pistons to test. Depending on the riding discipline, test pistons can accumulate anywhere from 8-30 harsh hours of run time before teams proceed with their grueling service schedules to keep their engines in top condition. Pistons are operated in machines competing in numerous types of racing, including pro-level motocross races all over the West Coast at tracks such as Glen Helen. Supercross and Arenacross teams have also actively run the pistons, including one that will be racing AMA Supercross in 2023. In-field testing is not just limited to racing applications. Wiseco furnishes pistons to select off-road and dual sport riders, some of whom are still accumulating hours on their original test pistons.
Wiseco has been working with select riders and teams to validate the new KTM piston design, from outdoor MX to Supercross style tracks to trail riding.
Inspections and Quality Control During Manufacturing
As with all Wiseco pistons, these redesigned KTM pistons are manufactured 100% in Wiseco’s Ohio, USA manufacturing facility. All the pistons Wiseco manufactures at their facility undergo in-process and end-of-line inspections. Each piston undergoes numerous machining operations to transform it from forging to the finished part. As the piston is being machined, each machine operator has a specific set of checks they perform to ensure the machining process is progressing correctly. These are their in-process inspections.
End-of-line inspections occur when the piston is completely finished and ready to ship. Before moving the piston from their manufacturing environment to their packaging area, a set of examinations are completed on the pistons to double-check that everything in the machining process was completed correctly.
Wiseco is unique because they control all aspects of its pistons’ design, forging, machining, and coating processes. This allows them to have complete oversight from start to finish and offers their customers a level of quality that many of their competitors cannot rival.
What Sets these KTM Pistons Apart from OEM and from Previous Wiseco Versions?
Revised forging and finished piston with updated boxed and strutted design to maximize strength needed for the high-performance nature of KTM, Husqvarna and GASGAS engines without compromising lightweight characteristics.
Updated piston skirt shape and ovality to improve operational stability and reduce frictional loss caused by cylinder wall contact, providing consistent ring seal and power and eliminating premature wear conditions.
Accumulator groove reduces pressure buildup below compression ring to greatly reduce the risk of ring flutter and aid in consistent ring seal, compression, and power.
Wiseco’s proprietary ArmorGlide skirt coating simultaneously reduces operating friction and minimizes wear.
Each updated KTM piston kit is supplied standard with a DLC coated wrist, which, in conjunction with double-broach pin oilers in the pin bores, greatly improves wrist pin and small-end lubrication for improved wear and longevity. Each piston also includes high-quality rings and circlips.
Available for late model KTM, Husqvarna, and GASGAS 350 and 450cc four-stroke models in standard and increased compression ratios. Complete application list below.
| Part Number | Make and Model | Model Year | Compression Ratio | Bore Size |
| 40264M08800 | Updated Design Piston KTM 350 SX-F, XC-F (’16-22) | ’11-15 ’16-22 | 13.5:1 14.0:1 | 88.00mm |
| 40264M08800 | Updated Design Piston KTM 350 EXC-F | ’20-23 | 14.0:1 | 88.00mm |
| 40297M09500 | Updated Design Piston KTM 450 SX-F, XC-F (’16-22) | ’13-17 ’18-22 | 12.6:1 12.75:1 | 95.00mm |
| 40278M09500 | Updated Design Piston KTM 450 SX-F, XC-F (’16-22) | ’13-17 ’18-22 | 12.6:1 13.5:1 | 95.00mm |
| 40306M09500 | Updated Design Piston KTM 450 SX-F Factory Edition | 2022.5 | 13.1:1 | 95.00mm |
| 40306M09500 | Updated Design Piston KTM 450 SX-F, XC-F | ’23-24 | 13.1:1 | 95.00mm |
| 40264M08800 | Updated Design Piston Husqvarna FC350, FX350 (’17-22) | 2015 ’16-22 | 13.5:1 14.0:1 | 88.00mm |
| 40264M08800 | Updated Design Piston Husqvarna FE350 | ’20-23 | 14.0:1 | 88.00mm |
| 40297M09500 | Updated Design Piston Husqvarna FC450, FX450 (’17-22), FS450 (’16-22) | ’14-17 ’18-22 | 12.6:1 12.75:1 | 95.00mm |
| 40278M09500 | Updated Design Piston Husqvarna FC450, FX450 (’17-22), FS450 (’16-22) | ’14-17 ’18-22 | 12.6:1 13.5:1 | 95.00mm |
| 40306M09500 | Updated Design Piston Husqvarna FC450 Rockstar Edition | 2022.5 | 13.1:1 | 95.00mm |
| 40306M09500 | Updated Design Piston Husqvarna FC450, FX450 | ’23-24 | 13.1:1 | 95.00mm |
| 40297M09500 | Updated Design Piston GASGAS MC 450F | ’21-23 | 12.75:1 | 95.00mm |
| 40278M09500 | Updated Design Piston GASGAS MC 450F | ’21-23 | 13.5:1 | 95.00mm |
| 40306M09500 | Updated Design Piston GASGAS MC 450F | 2023.5 | 13.1:1 | 95.00mm |
As leading OEMs continue to advance their designs and push the powersports industry forward, Wiseco will continue to find ways to improve upon those designs and set the bar even higher. Going deep into the design and development of Wiseco’s new 350 and 450cc pistons for KTM, Gas Gas, and Husqvarna models exemplifies how their team works together to identify, collaborate, and execute whenever they find a way to improve on a design, whether their own or an OEM’s design. There is no question that the process of bringing a new piston design to market is intricate and riddled with technical challenges. However, when executed to perfection, the resulting products are game changers.