Source: Cycle World
The 450cc motocross class is highly competitive and matured in the sense that what works is very well sorted out. What will Ducati bring to set its Desmo450 MX apart? Is desmodromic valve operation enough? (Ducati/)Ducati showed its Desmo450 MX prototype motocrosser along with a few words revealing that 2024 will be a development year for experimental factory prototypes, with production to begin in late 2025. How will Ducati’s significant background in racing help it compete against long-established players in motocross and supercross? Let’s examine some of Ducati’s design decisions for its new motocross racebike.Desmo450 Chassis DesignAs you can see, the chassis is a conventional welded aluminum structure that passes compactly around the desmo single-cylinder engine on its way from swingarm pivot to steering head. Why use aluminum, when it is both one-third the weight of steel and one-third of its stiffness? Where’s the advantage?We know that the stiffness of a tube increases very rapidly with diameter, but if we try to save weight this way with steel tubes, as we increase their diameter their wall thickness becomes so thin that its buckling resistance is inadequate. It is also a problem to feed concentrated loads (engine mounts, steering head, swingarm pivot) into very thin steel tubes. The local doublers and gussets this requires will kill any weight savings. Here aluminum offers an advantage; with the same weight per foot as a very thin steel tube, aluminum’s wall thickness can be three times that of steel, giving it much increased buckling resistance. This is what lies behind the modern substitution of aluminum for steel in motorcycle chassis—including this one.Aircraft structures are the ultimate expression of these principles: The fuselage is a thin-walled tube of very great diameter. This makes it highly efficient in terms of the weight required to achieve a given stiffness.Ducati Desmo Motocross EngineThe question on everyone’s lips is, how will Ducati use its unique direct, springless valve operating system (“desmodromic”) to gain a performance advantage? In this system, each valve is opened conventionally by a cam lobe and finger follower, but is closed not by a spring but by a second cam lobe, operating an L-shaped closing lever that positively pulls the valve closed. Ducati, coming late to this party, has the opportunity to study the best solutions of other makers, and possibly to identify areas in which Bologna can improve upon them. (Read this tech piece for more on desmo valve operation.) Sometimes a fresh look is better than years of staring!Related: Choosing Materials For Motorcycle Manufacturing Is More Complicated Than You ThinkThis is desmodromic valve operation from Ducati’s classic two-valve-per-cylinder engines (four-valve is identical in theory). Cam lobe 1 opens the valve and cam lobe 2 closes the valve. Barely shown are light “helper” springs—the coils can be seen on the lower shaft closer rocker arm. This aids start and idle by holding the valve more positively to the seat. (Jim Hatch/)The trend in giving engines strong, wide powerbands is to shorten valve-open time and increase lift. In MotoGP, Ducati has shown that it can do this at least as well as its pneumatic-spring competition. This means lifting valves higher than before, in less time than before—that is, at higher levels of acceleration. This is exactly where the limitations of steel springs hurt performance.Back in 2006, constructors who had started in MotoGP with conventional steel valve springs were having to replace them with pneumatic spring systems. To make steel springs do the job, they were having to increase their working stress, and that was fatiguing the material so fast that teams were changing springs every night on race weekends. They could make metal springs reach competitive rpm only by reducing valve acceleration, and that in turn meant reducing valve lift. The only alternative to reduced lift was longer valve timing, giving acceleration-limited steel springs more time in which to reverse the motion of a rapidly lifted valve and then return it to its seat. But extended valve timings narrow an engine’s torque band, moving it to the upper rpm range, weakening bottom-end and midrange. This makes engines harder to ride.Steel springs have been standard in MX for years, sometimes further loaded with the added moving mass of rocker arms. During recent years we have seen so-called “beehive” steel springs somewhat improve valve control, and surely there have been refinements in spring wire material. Yet even with such changes, no one in MotoGP has gone back to steel springs. On street engines, steel springs are by far the most chosen means for valve control and even Ducati has opted for springs on some of its current street engines. Read this tech piece with detailed photographs on the differences between the Panigale V-4 desmo engine and the V-4 Granturismo spring-head engine for a closer look at Ducati four-valve heads. Expect the Desmo450 MX to mimic the design of the Panigale’s head.Ducati, armed with its highly developed desmo system, should therefore be better able to make the 450MX engine’s valves follow the short-duration, higher-lift cam profiles that deliver a torque band that is both strong and wide. That in turn should make the 450 less challenging to ride.Turbulence Is KeyA further possible advantage Ducati can bring to any new engine design is the company’s long and deep experience in making combustion more efficient by speeding it up (the slower combustion is, the longer the time it spends losing heat to surrounding cooler metal). Remember the early days of World Superbike, when Ducati was constantly changing its bore or stroke? The racing department had learned how to generate the necessary combustion-accelerating mixture turbulence by varying both the diameter and downdraft angle of an engine’s intake ports. The smaller the intake diameter, the higher the velocity, which can “punch up” a weak midrange. More intake downdraft emphasizes cylinder filling, while less generates a rotating vortex that we call tumble: As the piston approaches TDC on its compression stroke, the energy in this vortex is transformed into turbulence that speeds combustion.The Desmo450 MX prototype has machined engine cases, not cast as would likely be for production. Ducati is exceptionally well studied in the ways of intake airflow. This coupled with desmodromic valve operation could lead to an exceptionally flexible and powerful 450cc motocross engine. (Ducati/)These principles are well known today, but Ducati has great experience in their use.Riders always prefer strong, wide, predictable power to power that’s mainly at the top. A person associated with the Kawasaki Supercross/motocross effort recently said the current factory KX450 racebikes make less peak power than previous production versions due to emphasis on midrange.Many have in the past believed that desmo Ducatis make more power because there are no valve springs exerting extra pressure on the mechanism. In high-rpm race engines, friction may consume as much as 25 percent of their gross horsepower, but valve drive has been shown to contribute only a small fraction of that. And if the power notionally saved by desmo wins races, why did Ducati win no MotoGP championship in the 14 seasons between 2008 and 2021?Let’s watch what happens in 450 MX in 2024 and 2025.
Full Text:
The 450cc motocross class is highly competitive and matured in the sense that what works is very well sorted out. What will Ducati bring to set its Desmo450 MX apart? Is desmodromic valve operation enough? (Ducati/)
Ducati showed its Desmo450 MX prototype motocrosser along with a few words revealing that 2024 will be a development year for experimental factory prototypes, with production to begin in late 2025. How will Ducati’s significant background in racing help it compete against long-established players in motocross and supercross? Let’s examine some of Ducati’s design decisions for its new motocross racebike.
Desmo450 Chassis Design
As you can see, the chassis is a conventional welded aluminum structure that passes compactly around the desmo single-cylinder engine on its way from swingarm pivot to steering head. Why use aluminum, when it is both one-third the weight of steel and one-third of its stiffness? Where’s the advantage?
We know that the stiffness of a tube increases very rapidly with diameter, but if we try to save weight this way with steel tubes, as we increase their diameter their wall thickness becomes so thin that its buckling resistance is inadequate. It is also a problem to feed concentrated loads (engine mounts, steering head, swingarm pivot) into very thin steel tubes. The local doublers and gussets this requires will kill any weight savings. Here aluminum offers an advantage; with the same weight per foot as a very thin steel tube, aluminum’s wall thickness can be three times that of steel, giving it much increased buckling resistance. This is what lies behind the modern substitution of aluminum for steel in motorcycle chassis—including this one.
Aircraft structures are the ultimate expression of these principles: The fuselage is a thin-walled tube of very great diameter. This makes it highly efficient in terms of the weight required to achieve a given stiffness.
Ducati Desmo Motocross Engine
The question on everyone’s lips is, how will Ducati use its unique direct, springless valve operating system (“desmodromic”) to gain a performance advantage? In this system, each valve is opened conventionally by a cam lobe and finger follower, but is closed not by a spring but by a second cam lobe, operating an L-shaped closing lever that positively pulls the valve closed. Ducati, coming late to this party, has the opportunity to study the best solutions of other makers, and possibly to identify areas in which Bologna can improve upon them. (Read this tech piece for more on desmo valve operation.) Sometimes a fresh look is better than years of staring!
Related: Choosing Materials For Motorcycle Manufacturing Is More Complicated Than You Think
This is desmodromic valve operation from Ducati’s classic two-valve-per-cylinder engines (four-valve is identical in theory). Cam lobe 1 opens the valve and cam lobe 2 closes the valve. Barely shown are light “helper” springs—the coils can be seen on the lower shaft closer rocker arm. This aids start and idle by holding the valve more positively to the seat. (Jim Hatch/)
The trend in giving engines strong, wide powerbands is to shorten valve-open time and increase lift. In MotoGP, Ducati has shown that it can do this at least as well as its pneumatic-spring competition. This means lifting valves higher than before, in less time than before—that is, at higher levels of acceleration. This is exactly where the limitations of steel springs hurt performance.
Back in 2006, constructors who had started in MotoGP with conventional steel valve springs were having to replace them with pneumatic spring systems. To make steel springs do the job, they were having to increase their working stress, and that was fatiguing the material so fast that teams were changing springs every night on race weekends. They could make metal springs reach competitive rpm only by reducing valve acceleration, and that in turn meant reducing valve lift. The only alternative to reduced lift was longer valve timing, giving acceleration-limited steel springs more time in which to reverse the motion of a rapidly lifted valve and then return it to its seat. But extended valve timings narrow an engine’s torque band, moving it to the upper rpm range, weakening bottom-end and midrange. This makes engines harder to ride.
Steel springs have been standard in MX for years, sometimes further loaded with the added moving mass of rocker arms. During recent years we have seen so-called “beehive” steel springs somewhat improve valve control, and surely there have been refinements in spring wire material. Yet even with such changes, no one in MotoGP has gone back to steel springs. On street engines, steel springs are by far the most chosen means for valve control and even Ducati has opted for springs on some of its current street engines. Read this tech piece with detailed photographs on the differences between the Panigale V-4 desmo engine and the V-4 Granturismo spring-head engine for a closer look at Ducati four-valve heads. Expect the Desmo450 MX to mimic the design of the Panigale’s head.
Ducati, armed with its highly developed desmo system, should therefore be better able to make the 450MX engine’s valves follow the short-duration, higher-lift cam profiles that deliver a torque band that is both strong and wide. That in turn should make the 450 less challenging to ride.
Turbulence Is Key
A further possible advantage Ducati can bring to any new engine design is the company’s long and deep experience in making combustion more efficient by speeding it up (the slower combustion is, the longer the time it spends losing heat to surrounding cooler metal). Remember the early days of World Superbike, when Ducati was constantly changing its bore or stroke? The racing department had learned how to generate the necessary combustion-accelerating mixture turbulence by varying both the diameter and downdraft angle of an engine’s intake ports. The smaller the intake diameter, the higher the velocity, which can “punch up” a weak midrange. More intake downdraft emphasizes cylinder filling, while less generates a rotating vortex that we call tumble: As the piston approaches TDC on its compression stroke, the energy in this vortex is transformed into turbulence that speeds combustion.
The Desmo450 MX prototype has machined engine cases, not cast as would likely be for production. Ducati is exceptionally well studied in the ways of intake airflow. This coupled with desmodromic valve operation could lead to an exceptionally flexible and powerful 450cc motocross engine. (Ducati/)
These principles are well known today, but Ducati has great experience in their use.
Riders always prefer strong, wide, predictable power to power that’s mainly at the top. A person associated with the Kawasaki Supercross/motocross effort recently said the current factory KX450 racebikes make less peak power than previous production versions due to emphasis on midrange.
Many have in the past believed that desmo Ducatis make more power because there are no valve springs exerting extra pressure on the mechanism. In high-rpm race engines, friction may consume as much as 25 percent of their gross horsepower, but valve drive has been shown to contribute only a small fraction of that. And if the power notionally saved by desmo wins races, why did Ducati win no MotoGP championship in the 14 seasons between 2008 and 2021?
Let’s watch what happens in 450 MX in 2024 and 2025.
