A motorcycle exhaust is a complex design. The more modern the model, the more intricate it is. Moreover, the operation of most options is directly related to electricity. For example, if you remove the chip, the “iron horse” may not start at all, but simply blink a light. We will focus on how a motorcycle muffler works, its operating principle and parameters. Thanks to this information, you can quickly figure out the cause of the breakdown, a change in the sound of the running engine.
Modern motorcycle models are equipped with sound-absorbing or resonator mufflers. In rare cases you can find a combined system. Most often, resonator mufflers are installed. However, lovers of rumbling sound prefer sound-absorbing types made of stainless steel or aluminum. They are also distinguished by their aesthetic appearance and improve “breathing”. Models made from other materials are more expensive.
Titanium mufflers have proven themselves to be particularly durable. That's why they are chosen by lovers of active driving. Installation of this type helps to minimize the possibility of damage to the muffler when colliding with an asphalt surface.
How does the exhaust work?
The main responsibility is to ensure that the air is vented and cooled so that the reflected gas flows back to the outlet before it opens. However, some people forget about this, focusing only on sound quality. So, the muffler also:
- Improves engine fillability, increasing its power.
- Extinguishes the flame from the remaining fuel.
- Reduces noise levels.
Ideally the exhaust works like this:
- the intake valve opens;
- a wave of reduced pressure is created going to the air filter;
- near the end of the pipe, the flow is partially reflected, resulting in high pressure;
- the exhaust valve opens;
- the high pressure jet passes to the very end of the exhaust system;
- gases are reflected, turning into a low-pressure wave.
To cool gases efficiently and quickly, they must expand . To do this, the volume of the exhaust system must be significantly larger than the volume of the cylinder.
According to the rules, the length of the intake tract is designed so that the reflected gas flows back directly to the valve opening. In this case, the filling of the cylinder becomes greater, which increases the power of the motorcycle. The reflected waves, returning to the new outlet, help remove the exhaust gas.
If the gas returns to the valve while it is still closed, then when it opens it will direct some of the waves back.
Extinguishing the flame, cooling the gases and venting them to the rear of the motorcycle
This is the second most important function of the exhaust, protecting primarily the driver, and not the device itself. It is strictly not recommended to start a motorcycle without a muffler, because flames fly out of the pipe, which can cause irreparable harm.
Hot gas must be cooled - this is what pipes do . To prevent smoke and hot air from causing inconvenience to the driver, the pipe is routed to the rear of the vehicle. The most optimal exhaust location is when the pipes are not directed towards sensitive parts of the motorcycle. Some people forget about this, which causes panniers or other plastic parts to become scorched.
Environmental friendliness
Currently, much attention is paid to ecology. Therefore, modern models are equipped with complex exhaust systems with catalysts and filters.
Noise reduction
This is not such an important option, but you can’t do without it. When the exhaust is properly tuned, the motorcycle produces that velvety “purr” that pilots love so much. However, sound is not a design goal, but only an accompanying characteristic.
No one likes a high, rough exhaust tone - a lower timbre is much more pleasant to the ear. For this reason, many drivers chase beautiful rumbling sounds, and after installing such an exhaust they find out that they have additionally increased the power of their iron horse. A well-tuned and functioning exhaust can improve the performance of a motorcycle.
Technical features of a saxophone muffler on a scooter and its operating principle
Almost no scooter, even the most minimal tuning, is complete without a resonant exhaust. What can we say about the sporting modifications of your “motohorse”. When does this make any sense, and when is it very desirable to visit a motorcycle parts store and buy a new saxophone muffler for your scooter?
We will talk about the advisability of such a purchase for a scooter with a two-stroke engine in a separate article, where we will look at the main model range, analyze the price segment of “saxophones”, and also help you choose the most successful resonators for both budget tuning and sports tuning.
A saxophone muffler for a scooter is not something you can buy just like that, so you won’t be able to navigate it by eye based on the model’s appearance. Before purchasing, it is necessary to carry out more than one stage of calculations, which will tell you which of all the models meets all the requirements and parameters. The key aspects will be the engine size, its model, tuning already done, then you should decide on the budget and the list of tasks. I would like to emphasize that there are no “penny” saxophone mufflers. Even the most modest models will start from one hundred US dollars, not to mention the more “cool” options.
Chinese resonators are completely different from conventional mufflers. The Chinese saxophone-type exhaust pipe is a product that is visually very similar to a resonator, but in fact it is not one. When the design stage took place, neither the volume of the pipe, nor its dimensions, nor the dimensions of the cones were taken into account. The main emphasis was placed solely on external similarity. If such motorcycle parts are installed at the factory (especially on four-stroke motorcycles), then this should be understood simply as a marketing ploy that does not carry any special load while riding.
What is the operating principle of a saxophone muffler on a scooter?
According to its principle of operation, the operation of the resonator should resemble the operation of a powerful turbine, with an increase in the compression of the mixture inside the cylinder. When operating a scooter with a two-stroke engine, the fuel-air mixture is partially lost (just during compression-intake). The main function of the resonator is the need to create a certain pressure inside the pipe, and for this purpose certain amounts of exhaust gases are restrained. In this case, the fuel-air mixture cannot freely exit the channel, the combustion chamber is almost completely filled with gases, and the pressure in it increases several times. All this leads to an increase in the power of the engine itself.
As the piston begins to move downwards, the exhaust port begins to gradually open, which triggers a series of different events in the resonator, which in turn increases the torque and power of the engine. Immediately after ignition (in a two-stroke engine), the mixture opens the exhaust channel and rushes into the exhaust pipe. Its speed reaches enormous sizes, so a wave with positive pressure is created.
The “exhaust stroke” indicator is the time during which the exhaust channel opens and the moment of intake occurs. It shows how long it takes for hot exhaust gases under pressure to enter the resonator. As soon as this happens, the necessary vacuum is immediately created in the combustion chamber, and a fresh portion of the fuel mixture ignites, starting the process again.
Then the wave with negative pressure begins its “work”. The process starts in the combustion chamber, where negative pressure is created around the intake channel. Gases escaping at maximum speed have, by their nature, greater inertia. Thanks to this negative pressure, another portion of the fuel-air mixture enters the combustion chamber, and part of it is immediately sent to the exhaust pipe (both channels remain open for a short period of time).
This is the operating principle of a two-stroke engine. Then the negative wave is replaced by a positive one. And all because the exhaust gases, flying into the pipe, expand in the first cone, and passing through the saxophone muffler, they hit the opposite wall and sharply narrow. They remain in the resonator for some time without coming out. And part of it manages to return back to the exhaust channel area, preventing a vacuum from forming in the combustion chamber of the scooter engine.
Shape and length
As mentioned above, the volume of the exhaust pipe must be greater than the volume of the cylinder. Therefore, a short pipe will have less effect than a long one. In addition, hot gas from a short system will be dangerous for the pilot.
The shape of the structure should be round. At sharp corners, air movement will begin to slow down, causing the bends to become hot, resulting in a crack appearing over time.
The exhaust configuration also refers to the shape - these are pipes coming out of the cylinders. There may be different numbers of them:
- 2 in 1 system;
- 4 in 1 system;
- 4, turning into 2, and then into 1 system;
- other spider-like options connected by a common diffuser.
It depends on the motor itself. On two-stroke machines they usually have a separate pipe per cylinder. The volume of the exhaust then exceeds the volume of the engine so much that the air waves can expand enough at the exhaust to cool completely.
Why do you need a tuning muffler?
Tuning companies produce a huge number of wonderful mufflers for the most popular European, Japanese, Taiwanese and Korean scooters. You can always choose a specific model for any budget. The price in this case depends on the complexity of the design, quality, and popularity of the scooter model for which it is designed. However, it's worth it.
After installing a high-quality and correctly configured resonator on a two-stroke scooter, you can expect an increase in power of up to 25% only after professional adjustments to the power system. This is a considerable figure, considering that in tuning, for example, for racing, the struggle is for every millisecond during the competition. For everyday life this is not so important, and the difference in power increase between 20 and 25% is difficult to notice, but experienced scooter riders will not remain indifferent after installing a branded saxophone.
An exhaust manifold
In motorcyclist slang it is called a “knee” due to its similar curve.
The most popular configuration system is 4 in 1. That is, the manifold has 4 outlets per cylinder, connecting into a single one and leading to the muffler. Suitable for driving at high speeds, and therefore it is often chosen by motorcyclists.
Long connection manifolds are less common, but are ideal for new riders because the bike's performance improves at different rpms.
This system is most often made of stainless steel because it receives the first wave of hot air. If it is made, for example, of cast iron, then the condensation formed after turning off the engine can lead to corrosion. Stainless steel is not afraid of this, plus it is quite durable.
In some cases, collectors are made of ceramics. However, this is in demand mainly among professional pilots, since this material is good only because it is relatively light in weight. The main disadvantage is that it wears out extremely quickly.
Muffler on a two-stroke
But muffler for two-stroke engines are much more complex in production, settings and selection for each specific model for specific tasks.
The principle of operation of the exhaust system for two-stroke bikes is known and was discussed in the section “Scooter design”. It is known that part of the power is returned to the engine from the exhaust system during operation at certain speeds. If this whole process is implemented ideally, after tuning the muffler the scooter will be unrecognizable. Naturally, if other components were tuned before. After a general boost of the scooter, the stock muffler is not enough for adequate engine operation throughout the entire speed range and replacing the muffler with a tuning one is perhaps the only way to make your scooter run faster and more dynamically.
Muffler
The very part that is capable of changing the timbre of the exhaust. This is what pilots reinstall when they want to change the sound.
Various gadgets can be installed inside the muffler. The most common:
- Catalysts and filters help bring emissions to an environmentally friendly level. Found in more modern models.
- Db Killer is a system that has many channels with holes that allow air waves to pass through. It increases resistance to gas flows. Without such a “flute”, the exhaust system will become similar to a forward flow with a completely different sound.
Some motorcycles allow you to open and close the throttles using a button on the handlebars. This helps to change the sounds and exhaust according to the situation. The most famous brand of such a system is Dr. Jekill & Mr. Hyde, which can be installed on many devices.
When considering how a motorcycle muffler is designed, one cannot help but mention the power valve. It distributes the reflected waves of air flow. This is necessary to prevent gas from reaching the exhaust valve when it closes. The valve only allows waves to fill the cylinder and rid it of recycled air. Most often used in manufacturing: titanium, aluminum, carbon, stainless steel.
