Every self-respecting motorcyclist spends a lot of time and effort on improving his own apparatus. By increasing the power of the engine, improving the performance of the tank, the focus eventually shifts to the exhaust system. A brand new forward flow to a motorcycle, installed with your own hands, will delight the eyes and ears of the driver. The modernized exhaust system on motor vehicles looks much more stylish, aesthetically pleasing, and a loud sound makes the bike noticeable on the road and helps to avoid unpleasant situations.
What is forward flow?
Direct flow is a structure for moving liquids and gases in a single direction. From the factory, the motorcycle is supplied with a standardized exhaust system, but subsequently customizing the bike and increasing its power of the original configuration is no longer enough - the amount of exhaust gases increases. Specialists install a forward flow system, visually and technically ennobling your motorcycle (the power will increase by 3 - 5 Horse power), but it's much more pleasant to do it yourself. This will not require a lot of time, the materials are readily available, it remains to arm yourself with information.
How to make a muffler for a motorcycle?
· Unscrew the fixing screws and remove the old factory muffler.
· Pull out the standard guts - tubes and other offal.
· Purchase a thin-walled tube or make it yourself from improvised garage materials. Stainless steel or aluminum without defects are the best option... Furrows, chips and holes will give the forward flow an unpleasant metallized noise, and the incorrect dimensions of the tube will impede the gas exhaust. Be careful when creating a muffler for a motorcycle with your own hands: maintenance requirements should not be violated.
· The outer shell of the muffler and the thin inner tube differ significantly in volume, it is recommended to fill the gap between them tightly with glass wool - this will help reduce noise. The risk of fire for the glass wool is minimized by wrapping the pipe with a fire-resistant substance or asbestos.
· Using the fasteners, attach the muffler back to the motorcycle, cover the exhaust part with a lid and check the result of our manual work. When the bike starts, you should hear a slight bass tone. If you want more expressive effects in the forward flow sound, there is another way to create a silencer, which we will discuss below.
How to create a sonorous forward flow to a motorcycle with your own hands?
· There are a large number of types of forward flow: some increase the power, others improve the sound, the third category of forward flow gives a double result.
· The essence of the work of a high-quality forward flow is to control gases and liquids in a motorcycle heat exchanger, directing substances blocked by a wall in a single direction.
· Having conceived your own forward flow project, be sure to check out the videos of the workshops posted on the network. With experience and engineering thinking, you can experiment and invent new types of cocurrent flows.
· A welding machine and a grinder will help you to make a unique muffler for a motorcycle with your own hands. To do this, we buy sheet stainless steel, roll it up into a pipe, fastening the individual elements with arc-argon welding. The inner tube is made in the same way, only in a smaller diameter, and many small holes are drilled in the steel sheet beforehand. At the final stage, end caps are attached.
· The further process resembles the replacement of the original muffler with a homemade one. Stuffed with glass wool, covered with asbestos. It is necessary to fill the space between the shell and the tube more densely, then vibration and noise during driving will be less.
· Some specialists convert car mufflers to motorcycle ones, how do they do it and what does it give? The only difference is the excellent motorcycle and auto mounts, which can be tweaked with a welding machine. Seams are covered with chrome paint. At the output, we get a stylish velvet sound of forward flow and increased power indicators. A pleasant bonus is job satisfaction and tangible cost savings.
Information on how to make a muffler for a motorcycle is very popular not only among tuning specialists and craftsmen with golden hands. We believe that every motorcycle enthusiast should have this knowledge, given the simplicity of the workflow and the availability of materials.
Instructions on how to independently give a new and beautiful look to an old scooter muffler, and at the same time make it quieter.
Point 1. For work we need.
Materials:
A piece of thin stainless steel, 0.4-1 mm thick.
A piece of fabric, rolled heat-resistant sound absorber, ~ 5 mm thick.
Instruments:
Semi-automatic welding.
Grinder with a thin disc 1 mm.
Clause 2. Reasons.
Over time, even from the most eminent manufacturers of motor vehicles, as in this case Honda, there is a complete clogging of the muffler with exhaust deposits, after which the engine does not start and there are only two ways out, buy a new Chinese muffler or disassemble and clean the old one.
But since the Chinese muffler completely lacks a reverse resonance wave system, that is, this is just an empty can, which is also very thin, and as a result, for a two-stroke motor, this is a power loss of up to 50%, and as a result, the scooter completely stops driving!
During disassembly of the muffler, it is necessary to forcefully remove the internal sound absorber of the fiberglass body, after which the sound of the scooter working becomes louder and nasty (ringing), that is, the body bank itself rings and resonates, and appearance not as neat as before.
Therefore, self-installation of an additional decorative case with an additional noise absorber will be very useful.
Clause 3. Manufacturing and installation.
We unscrew and remove the muffler.
We measure the circumference of the muffler can and the length between the welds.
To the obtained dimensions of the circle, add 2-3 cm for overlap, and to the width of 2 cm for bends.
Cut out a calculated rectangle from thin stainless steel.
On both sides of the wide side, we make bends of 5-6 mm.
We polish the surface with GOE paste.
We make cuts with a thin disk with a step of 5 mm.
We remove sharp edges and burrs.
According to the resulting dimensions, we cut out a piece of a sound absorber (for example, weave asbestos, fiberglass, etc.) so that it fits tightly inside between the bends.
We wrap the muffler around the can so that the joint is on the back side.
For the convenience of welding, we fix it with clamps or other fasteners (for example; rubber rings).
We make spot welding.
It is difficult to imagine a sports or tuning city car without a straight-through muffler. The noble roar of the engine pleases the keen ear of the owner, thrills the girls, arouses the envy and admiration of friends. However, neighbors do not always like this, and the traffic police prefers a quiet forward flow. This is where the driver faces the question: what to do to muffle it, what methods are used to make the exhaust quieter.
Why do you need a forward flow and why sometimes it needs to be muted
A car with an exhaust louder than 96 dB will not be able to pass a technical inspection and will not cross the border - in Europe, traffic rules are strict, and police officers are incorruptible. Even in motorsport, the sound is limited. Only Formula 1 promoters do not like the attempt to drown out the noises from cars. They even opposed new regulations for switching from eight-cylinder to V6 engines, fearing for the prestige of racing.
Having conceived to muffle the forward flow with your own hands, you need to clearly understand the principles of the coordinated release, and determine the purpose of the car tuning performed. The improvement in dynamic performance is only due to the installation of a new "spider" - the exhaust manifold. The rest of the components of the exhaust system simply should not create resistance to gases and have a bad effect on the result.
When properly tuned, the resonant exhaust provides a 3-9% increase in torque for naturally aspirated engines and more than 10% for turbocharged engines. But in production cars the increase in the rate of filling the cylinders with the working mixture during modernization is less than 2–3%.
The installation of a direct-flow muffler on ordinary stock cars is needed only as a decorative option, for a pleasant tone of the exhaust. The main criterion for the quality of the direct flow on a serial machine is the euphony and velvety noise of the engine, and not the increase in power. The car will shout louder or quieter - at high-speed and dynamic characteristics it will not be reflected. In this case, when there is an urgent need to drown the forward flow, you can do this without thinking about the consequences.
What is a flute in a straight-through muffler, and what is the effect of it
To make the forward flow quieter and to get "through" decibels at the output, a simple design is used, which motorists call a flute. This is a piece of perforated pipe 180–250 mm long and a little more than 1/3 of the exhaust diameter, with a welded washer-plug in the form of a disk, cylinder or cone, which is bolted inside the forward flow, at the air cut, thereby allowing it to be muffled. 
The principle of operation of a flute for direct flow is that when the cross-section of the exhaust channel changes, and the exhaust gases exit through the perforations, the following occurs:
- change in speed and pressure;
- the sound wave breaks;
- the volume is reduced by 3-4 dB, the exhaust becomes quieter.
The correct name for this flute is silencer, and it comes with expensive exhaust systems that are sold online. You can also purchase it separately, the average price of good European models is 70–150 dollars, and mass ones from the Middle Kingdom - from 450 rubles.
Do-it-yourself flute for forward flow
If you have the desire and skill, then making a flute with your own hands in order to drown out the forward flow is not difficult at all. It will turn out to be cheaper than a branded one, but not always better than a Chinese one. 
For work, you need a steel (preferably stainless) pipe 20 mm and a piece of sheet metal 0.8-1.2 mm thick. It is desirable to cook by arc welding, observing the rules for working with stainless steel. A plug pre-bent from a sheet of steel with holes for fastening is welded to the pipe. It can be screwed on with three M8 screws, but for installation in a few minutes, one threaded connection is enough.
When manufacturing, you need to try to accurately measure the inner diameter of the muffler at the air cut, so that the plug fits loosely, but without a gap. Then, when entering the track, you can quickly remove the flute from the hot pipe with a pair of wrenches or pliers. 
It is important to remember that any obstruction in the exhaust pipe, including the silencer, will inevitably reduce engine power. Making it quieter and muffling without loss will definitely not work.
To make a quiet direct-flow muffler, but not to lose the additional power, which is provided by the modernization of the exhaust tract, use a direct-flow damper. This exhaust design has been known for a long time and is found in many BMW models (more often with a manual transmission).
When the engine is running at low power, when the advantage of the coordinated exhaust is not used, the exhaust gases exit through a conventional muffler, and the direct-flow one is closed by a damper. At optimal speeds, the damper opens the direct flow outlet, and the motor delivers maximum torque due to the enhanced ventilation of the cylinders.
The damper control is automatic, but there are also manual models. In the city, such a car almost does not differ from a stock car in sound, and on the highway it not only sounds like a tuning car, but has a real increase in power. It is not cheap - for a full machine gun, complete with a titanium "spider", the price often exceeds a couple of thousand dollars.
Similar in capabilities, but not very eminent analogues, are moderately priced, but it is better to select the appropriate option with a specialist - for the success of such an upgrade, the knowledge of a mechanic engineer may be required. 
The budget version of the forward flow with a damper can also be welded independently from scrap materials. The upper part from the old carburetor is suitable for the damper, if you remove the cable idle move to the salon. Making such a structure with your own hands, it will take much more effort and time than for a homemade flute, and the result of the installation cannot be predicted in advance. Muting the sound is easy, but to conserve power, even if you're lucky, you have to tinker with the tuning.
Output
Whichever option you choose to muffle the exhaust, you should understand that you can just buy a ready-made solution if finances allow, or you can muffle it with your own hands, making a device from available tools.
Text: Artem "S1LvER" Terekhov
Exhaust - motorcycle or scooter exhaust system
The rumbling of a V-shaped line, the harsh howl of a sports Japanese rower, the unhurried rattling of an in-line British two ... These are the associations that an ordinary person has when they say "exhaust system". Designers and engineers see everything a little differently, from a harsh technical side. We will not get into deep jungle, but simply form an idea of how the "exhalation" of our motorcycles works, and we will try to make it as interesting as possible.
Theory, theory ...
The main tasks set for the exhaust system are to remove the gases leaving the combustion chamber, cool them and reduce the noise level. Imagine what it would be like if hot exhaust was blown out of the cylinder straight into the atmosphere! Of course, the front tire would melt together with the fender, and the engine noise level would become simply unbearable (for fun, try removing the exhaust system and starting the engine. Let's see how long your tender ears last). In addition, if a little unburned fuel remained in the exhaust, it would effectively burn out upon contact with atmospheric oxygen. Therefore, the exhaust system directs the exhaust gases to the "tail" of the motorcycle, cooling them and eliminating unwanted combustion tendencies in the atmosphere.
Another task of the exhaust system is to use the pressure pulsations generated at each working stroke. This is done to improve cleaning and filling of the combustion chamber.
Typically, the factory exhaust system is made of steel. Depending on the style requirements, the steel is chrome plated or painted with heat-resistant paint. Sometimes, although it is more expensive, stainless steel is used.
The bike also has a pulse
During each combustion stroke, waves are generated in the exhaust pipe as the gas moves high pressure... It is logical to assume that the high pressure wave is followed by the wave low pressure... At some point in the exhaust system, which is determined by the designers, part of the high pressure waves collide with the system, while the remaining high pressure wave leaves the pipe, the low pressure wave following it is reflected back. The low pressure wave fills the combustion chamber with a fresh air-fuel mixture. The reflected high pressure wave then prevents fresh mix from flowing out through the outlet. The next low pressure wave removes the exhaust gases from the combustion chamber. The process is repeated, the motorcycle breathes smoothly and well.
The length of each pipe of the exhaust system is carefully calculated so that the pressure pulsations are at the required point at a given moment in time. A properly executed release plays a decisive role in high performance engine. Therefore, you should not buy the "ends" of little-known basement firms. If you are already buying a tuning edition, do not spare money on a quality product from a reputable manufacturer.
The exhaust system is designed in such a way that best performance its work is provided in a narrow range of engine speeds. Therefore, various systems are used to improve engine performance over the entire speed range, which we will talk about later.
Valves are everywhere! Even in exhaust systems
Outside certain speeds, the engine runs relatively ineffectively. Yamaha specialists were the first to solve the problem, having developed the EXUP system (Exhaust Ultimate Power Valve, which in Russian means the monstrous "Absolute power valve of the exhaust system"). This design was the first mechanism for changing the internal section of the exhaust system, thus achieving maximum power over the entire range of engine operation. EXUP is located between the exhaust pipes and the muffler. The power valve is closed to medium speed, thereby reducing the pipe section, and open at high speeds, increasing the pipe section. It is controlled by the electronics and the servomotor. I wonder what was thinking this mechanism as an additional emission control measure, and was fitted to the FZR1000 in the California version, known for its tough eco-regulations. However, the engineers were surprised to find that the valve evens out the power response, and even slightly raises the horse population in the motor! After that, of course, EXUP began to be installed on many other bikes of the company, including the R1, MT-01 and FZ1.
The power valve is a special flap that partially overlaps the section of the exhaust pipe when the engine is resting at low and medium speeds to increase torque.
Later, solutions appeared from Suzuki called SET (Suzuki Exhaust Tuning), and from Honda - H-VIX (Honda Variable Intake \ Exhaust). They are not fundamentally different from the EXUP, only in the Honda version, separate valves are used in the exhaust pipes.
Two-stroke exhaust systems
The influence of exhaust on engine performance is much more significant here than on four-stroke (if it's not clear why, check out our article on this topic). A separate set of exhaust pipe and muffler, as well as a resonator is always installed on each cylinder.
The photo clearly shows the exhaust system with a resonator. Honda RS250R
The latter is optional, but allows for a significant increase in power due to the natural tendencies of exhaust pulsations to resonate within the exhaust system. The system is designed in such a way that the exhaust pipe gradually merges into a straight muffler cone, at the end of which there is a reverse cone ending with a small exhaust pipe. A properly tuned resonator ensures the best filling of the cylinder with the working mixture, which means high power indicators. This effect is unattainable in any other way.
How it works
When the exhaust port is opened, the gases are forced into the exhaust system, aided by the incoming fresh charge coming from the ports of the purge channel. Exhaust gases move in the form of waves along the resonator, gradually expanding and losing speed. When the wave reaches the backward cone, it contracts and is partially reflected back as a backward wave. The combustion chamber is overfilled at this point, and the excess mixture begins to fill the upper part of the exhaust pipe. As the piston closes the purge ports, the backwash reaches the exhaust port, returning excess mixture to the combustion chamber where it is trapped by the piston blocking the exhaust ports. In this way, a slight "boost" effect is achieved and the engine power is increased compared to normal conditions (that is, if the resonator were not present).
M. Coombs, "Motorcycles. Device and principle of operation."
The optimal time for this effect to travel to the exhaust ports is achieved at a certain engine speed, above and below which the engine operates as usual. To take full advantage of this effect, careful tuning of the system is necessary - this is the only way to realize the additional power and the famous two-stroke "pickup". Two-stroke motorcycles will always have their own character - they live a short (in terms of working speed), but bright life. Power valves are also used on two-strokes (again, about this in our article), but the lot of 2T bikes are high-speed grips somewhere near the red zone.
Oh, those green ones!
We know from chemistry that a catalyst is a substance that initiates a chemical reaction between other elements, but itself does not participate in the reaction. I incited one to myself. That is, the catalyst is not consumed, and its properties do not change. The KH itself is maintenance-free, but it is very fragile and can be damaged if the exhaust system is faulty, or if leaded gasoline or an incorrect air-fuel mixture is used. Leaded gasoline will clog the KN with deposits that no "domestos" will wash away.
Gold pipes Kawasaki ZX-10R 2008
KH is a porous structure that is installed in the exhaust system. The catalysts are platinum, palladium and rhodium, which are used alone or in compounds. They sit there in order to literally "neutralize" harmful emissions in the exhaust gases, as a result of chemical reactions converting CH, CO and NO X into simple water vapor, carbon dioxide and oxygen. The porous KH is made in order not to create resistance to flow and to increase the surface area to ensure that all harmful emissions react with the appropriate catalysts. And it is located exactly where it is located, because the reaction will take place only in a certain temperature range. In addition to the porous element, there is a chamber into which air is supplied, and in which reactions of converting harmful substances into harmless ones take place.
A catalyst, a reaction chamber, an ingenious muffler - the evil ZX-10R is very fond of nature!
This is the real joy of the ecologist, but ordinary riders are clearly disadvantaged here. After all, the catalyst makes the system a couple of kilograms heavier, and steals some of the performance from the motor (although KN is porous, but still it is much worse than if it simply was not there). It would seem - just take it and throw it away, it's just business! But no, the manufacturer puts electronic barriers. For example, the latest GSX-R1000s have a sensor that monitors whether an adrenaline-hungry KN owner has ripped out of the exhaust system. If there is no catalyst, the engine simply will not start, only a light on the tidy will gleefully burn. Conclusion: if you want to increase the number of notorious e-s, it is better to throw out the entire stock system, installing an aftermarket kit instead, and not forgetting to remove the annoying "glitch" in electronics. The tuning release will save weight and, with proper tuning, add power. I will modestly keep silent about the changed sound ...
And finally, the can!
The exhaust system of the serial bike ends with a muffler. Its task is to ensure the maximum free passage of gases while simultaneously removing excess energy, which is noise.
This is usually achieved through absorption. The escaping gases are slowed down due to their expansion in the muffler housing. Further, the pulses are crushed when passing through a metal mesh and packing made of mineral wool or similar material. When they finally find a way out, they will more or less subside - the goal has been achieved.
You can also divide the muffler body into many small "tunnels" through which the gases move in different directions along a rather winding path. Before leaving the exhaust pipe, the sound waves are reflected repeatedly, thereby losing energy.
Typically, both approaches complement each other and find space on board the same motorcycle.Such are the "vicissitudes" await noisy exhaust gases in the muffler liter Ninja.
The power valve is visible below, in this case located in front of the muffler itself.
Third-party muffler cans, which are designed to "improve sound and give a thousand horsepower," are essentially hollow tanks made of titanium, stainless steel, or carbon. There are no suppressing elements at all there, as well as increases in power. All you get is a modified sound, and not always in better side... It is worth knowing in advance how the bank you have your eye on "sings".Making a forward flow
For this work we need:
1.two pipes:
1.muffler inlet pipe diameter (standard);
2.diameter d20 cm, length 1m;
2. old muffler VAZ 2109."We disassemble the old muffler. Cut out the walls, take out the insides (see Figure 1.).
"We take pipe 1.1., In the place where it will be in the muffler we drill holes (see figure 2.).
"From the side indicated by the arrow (see Figure 3.) weld pipe 1.2 onto it using a metal plate.
"We put this structure inside the body of the old muffler, and weld it on both sides (Fig. 4.)
"We wrap the muffler with a heat-resistant insulating plate (eg paronite).
"We wrap the muffler with a sheet of stainless steel with an overlap of 5 cm at each end and 5 cm in length. You can buy stainless steel on the market. (Fig. 5.)
"We wrap the sidewalls and roll the joint. (Fig. 6)
"We weld on the ears for the holders and mount the muffler in place.About tuned exhaust
The article is taken from the magazine "Tuning" St. Petersburg
Perhaps the most popular topic in all "smoking rooms" one way or another related to car tuning is engine exhaust systems. At the very least, I am more likely to answer questions about emissions than about valves, heads, crankshafts and other components of engine tuning. Moreover, the range of questions is approximately the following: from "tell me, how to apply the formula for calculating the resonant frequency (the ratio for the Helmholtz resonator is given) to the four-throttle inlet?" before "a friend gave me a" spider "from his sports" golf ". How much horsepower will be added if I install it on my car?" or "I am building a motor for myself. What muffler should I buy for more power?" Moreover, in all matters, the additional power is the red line.
LET'S START, LET'S UNDERSTAND WHERE THIS ADDITIONAL POWER LIES. AND WHY THE EXHAUST LINE AFFECTS THE PERFORMANCE OF THE MOTOR.
If we all unanimously understand that power is the product of torque and crankshaft rotation speed (revolutions), then it is clear that power is a speed-dependent quantity. Consider a purely theoretical engine (it doesn't matter if it is electric, internal combustion or turbojet), which gives a constant torque from 0 to infinity. (curve 2 in Fig. 1) Then its power will grow linearly with revolutions from 0 to infinity (curve 1 in Fig. 1). The subject of our interest is four-stroke multi-cylinder internal combustion engines, due to the design and processes occurring in them, have an increase in torque with an increase in revolutions to its maximum value, and with a further increase in revolutions, the torque drops again (curve 3 in Fig. 1). Then the power will have a similar form (curve 4 in Fig. 1). An important factor for understanding the functions of the exhaust system is the relationship between torque and cylinder filling ratio.
Let's imagine the process taking place in the cylinder during the intake phase. Suppose the engine crankshaft rotates so slowly that we can observe the movement of the air-fuel mixture in the cylinder and at any moment of time the pressure in the intake manifold and the cylinder has time to equalize. Let's assume that the top dead center (TDC) pressure in the combustion chamber is equal to atmospheric pressure. Then, when the piston moves from TDC to the bottom dead center (BDC), an amount of fresh air-fuel mixture, exactly equal to the volume of the cylinder, will enter the cylinder. They say that in this case, the filling factor is equal to one. Suppose that in the above process we close the intake valve at the piston position corresponding to 80% of its stroke. Then we will fill the cylinder only to 80% of its volume and the mass of the charge will be respectively 80%. The filling factor in this case will be 0.8. Another case. Suppose, in some way, we managed to create a pressure in the intake manifold 20% higher than atmospheric pressure. Then, in the intake phase, we will be able to fill the cylinder by 120% by mass of the charge, which will correspond to a filling factor of 1.2. So, now the most important thing. The engine torque corresponds exactly to the cylinder fill factor on the torque curve. That is, the torque is higher there, where the filling factor is higher, and exactly the same number of times, unless, of course, we do not take into account the internal losses in the engine, which grow with the rotation speed. From this it is clear that the torque curve and, accordingly, the power curve is determined by the dependence of the filling factor on the speed. We have the ability to influence, within certain limits, the dependence of the filling ratio on the engine speed by changing the valve timing. In the general case, without going into details, we can say that the wider the phases and the earlier in relation to crankshaft the area we shift them, the maximum torque will be achieved at high revolutions. In this case, the absolute value of the maximum torque will be slightly less than with narrower phases (curve 5 in Fig. 1). The so-called overlap phase is essential. The fact is that at high rotational speed, the inertia of gases in the engine has a certain effect. For better filling at the end of the exhaust phase, the exhaust valve must be closed a little later than TDC, and the inlet valve must be opened much earlier than TDC. Then the engine has a state when, in the TDC area with a minimum volume above the piston, both valves are open and the intake manifold communicates with the exhaust through the combustion chamber. This is a very important condition in terms of the effect of the exhaust system on engine performance. Now, I think it's time to look at the functions of the exhaust system. I must say right away that there are three processes in the exhaust system. The first is a more or less damped outflow of gases through pipes. The second is the damping of acoustic waves in order to reduce noise. And the third is the propagation of shock waves in a gas medium. We will consider any of these processes from the point of view of its influence on the filling factor. Strictly speaking, we are interested in the pressure in the manifold at the exhaust valve at the time of its opening. It is clear that the lower the pressure, and better even below the atmospheric pressure, can be obtained, the greater the pressure drop from the intake manifold to the exhaust, the more charge the cylinder will receive in the intake phase. Let's start with some pretty obvious things. The outlet pipe serves to discharge exhaust gases outside the car body. It is quite clear that it should not offer significant resistance to the flow. If, for some reason, a foreign object appears in the exhaust pipe, blocking the flow of gases (for example, the neighbors joked and shoved potatoes into the exhaust pipe), then the pressure in the exhaust pipe will not have time to drop, and at the moment the exhaust valve opens, the pressure in the manifold will oppose cleaning cylinder. The filling ratio will drop, since the remaining large amount of exhaust gases will not allow the cylinders to be filled with the same fresh mixture. Accordingly, the engine will not be able to generate the same torque. It is very important to understand that the dimensions of the pipe and the design of the noise mufflers in a production vehicle correspond fairly well to the amount of exhaust gases generated by the engine per unit of time. As soon as a serial engine has undergone changes in order to increase power (whether it is an increase in displacement or an increase in torque at high rpm), the gas flow through the exhaust pipe immediately increases and the question should be answered, whether the serial exhaust system now creates excessive resistance in the new conditions ... So from the consideration of the first process outlined by us, it should be concluded that the dimensions of the pipes are sufficient. It is quite clear that after a certain reasonable size it is pointless to increase the pipe cross-section for a particular engine, there will be no improvement. And answering the question, where is the power, we can say that the main thing here is not to lose, it is impossible to acquire anything. From practice I can say that for a 1600 cc engine. cm, having a good torque up to 8000 rpm, a pipe with a diameter of 52 mm is quite enough. As soon as we talk about resistance in the exhaust system, it is necessary to mention such an important element as a silencer. Since in any case the muffler creates resistance to the flow, it can be said that the best muffler is its complete absence. Unfortunately, for a road car, only desperate boors can afford it. Fighting noise is, no matter how you turn it, taking care of our health. Not only in Everyday life, but also in motorsport there are restrictions on the noise produced by the car engine. I must say that in most classes sports cars exhaust noise is limited to 100 dB. These are quite loyal conditions, but without a muffler, no car will meet the technical requirements and will not be able to be admitted to the competition. Therefore, the choice of a muffler is always a compromise between its ability to absorb sound and low flow resistance.
NOW, PROBABLY, YOU SHOULD IMAGINE HOW THE SOUND IS EXTINGUISHED IN THE MUFFLER.
Acoustic waves (noise) carry energy that arouses our hearing. The task of the muffler is to convert the vibration energy into thermal energy. Silencers should be divided into four groups according to the way they work. These are limiters, reflectors, resonators and absorbers.
LIMITER
The principle of its operation is simple. In the muffler body there is a significant narrowing of the pipe diameter, a certain acoustic resistance, and immediately behind it a large volume, an analogue of a container. Pressing sound through the resistance, we smooth out the oscillations with volume. Energy is dissipated in the choke, heating the gas. The higher the resistance (the smaller the hole), the more effective the smoothing. But the greater the resistance to the flow. Probably a bad muffler. However, it is a fairly common design as a pre-silencer in the system.
REFLECTOR
A large number of acoustic mirrors are organized in the muffler housing, from which sound waves are reflected. It is known that with each reflection, part of the energy is lost, spent on heating the mirror. If we arrange a whole labyrinth of mirrors for sound, then in the end we will dissipate almost all the energy and a very attenuated sound will come out. Pistol silencers are built on this principle. A significantly better design, however, since we also force the gas flow to change direction in the bowels of the hull, we will still create some resistance to the exhaust gases. This design is most often used in end silencers of standard systems.
RESONATOR
Silencers of the resonator type use closed cavities located next to the pipeline and connected to it by a series of holes. Often in one case there are two unequal volumes, separated by a blind partition. Each hole, together with a closed cavity, is a resonator that excites natural frequency oscillations. The conditions for the propagation of the resonant frequency change sharply, and it is effectively damped due to the friction of gas particles in the hole. Such mufflers effectively damp low frequencies in small sizes and are mainly used as preliminary, first in exhaust systems. They do not provide significant resistance to the flow, because the section is not reduced.
ABSORBER
The way the absorbers work is to absorb acoustic waves by some porous material. If we send sound, for example, to glass wool, then it will cause vibrations of the fibers of the wool and friction of the fibers against each other. Thus, the sound vibrations will be converted into heat. Absorbers allow you to build a muffler structure without reducing the cross-section of the pipeline and even without bends, surrounding the pipe with holes cut in it with a layer of absorbing material. Such a muffler will have the lowest possible flow resistance, however it will reduce noise worst of all. I must say that serial exhaust systems use, in most cases, various combinations of all the above methods. There are two silencers in the system, and sometimes more. Attention should be paid to the peculiarity of the muffler designs, which in the case of self-made does not achieve effective noise reduction, although everything seems to be done correctly. If there is no absorbing material inside the muffler, then the walls of the housing become the source of the sound. Many have noticed that some mufflers have an asbestos lining on the outside, pressed by an additional sheet of a false casing. This is the measure that will limit radiation through the walls and prevent heating of adjacent elements of the car. This measure is typical for the first and second types of mufflers. There is one more circumstance that cannot be ignored in the tuning article. This is the timbre of the sound. Often the client's wishes to the tuning company are to achieve a "noble" sound of the engine by replacing the muffler. It should be noted that if the requirements for the exhaust system do not extend beyond the change in "voice", then the task is greatly simplified. We can say that, most likely, an absorption-type muffler is more suitable for such purposes. Its volume, the amount of packing, as well as the packing itself determine the spectrum of frequencies that are intensely absorbed. Almost any soft padding absorbs the high-frequency component to a greater extent, giving a velvety sound. Silencers of the resonator type dampen low frequencies. Thus, by varying the size, content and set of elements, you can choose the timbre of the sound.
NOW YOU CAN GO TO THE MOST POPULAR AND MORE DIFFICULT QUESTION. HOW CAN THE ENGINE GET ADDITIONAL POWER THANKS TO THE EXHAUST SYSTEM ADJUSTMENT?
As we have already seen, fill ratio, torque and power depend on the pressure difference between the intake and exhaust manifolds during the purge phase. The exhaust system can be constructed in such a way that shock waves propagating in the pipes are reflected from various system elements will return to the outlet valve in the form of a pressure surge or vacuum. Where does the rarefaction come from, you ask. After all, we always only pump into the pipe and never suck it off. The fact is that, due to the inertia of gases, a pressure jump is always followed by a rarefaction front. It is the rarefaction front that interests us the most. You just need to make sure that he is in the right place at the right time. We already know the place well. This is the outlet valve. And the time needs to be clarified. The fact is that the time of action of the front is very short. And the opening time of the exhaust valve, when the vacuum front can create useful work for us, strongly depends on the engine speed. And the entire period of the release phase must be divided into two components. The first is when the valve has just opened. This part is characterized by a large pressure drop and an active outflow of gases into the exhaust manifold. The exhaust gases leave the cylinder after the working stroke even without assistance. If the vacuum wave reaches the outlet valve at this point, it is unlikely to interfere with the cleaning process. But the end of the issue is more interesting. The pressure in the cylinder has already dropped to almost atmospheric pressure. The piston is near TDC, which means that the volume above the piston is minimal. Moreover, the intake valve is already slightly open. Remember? This state (overlap phase) is characterized by the fact that the intake manifold communicates with the exhaust manifold through the combustion chamber. Now, if the front of expansion reaches the exhaust valve, we can significantly improve the filling ratio, since even in a short time of action of the front, it will be possible to blow through a small volume of the combustion chamber and create a vacuum, which will help accelerate the air-fuel mixture in the intake manifold channel. And if we imagine that as soon as all the exhaust gases leave the cylinder, and the vacuum reaches its maximum value, the exhaust valve closes, we will be able to receive a charge in the intake phase that is greater than if we cleaned the cylinder only to atmospheric pressure. This process of recharging the cylinders using shock waves in the exhaust pipes can provide a high filling ratio and, as a result, additional power. The result of its action is approximately the same as if we pressurized the intake manifold using a compressor. After all, what difference does it make to how the differential pressure is created, pushing the fresh mixture into the combustion chamber, by means of injection from the intake side or vacuum in the cylinder? Such a process may well take place at the prom. ICE system... There was a mere trifle. It is necessary to organize such a process.
The firstA necessary condition for recharging the cylinders with the help of shock waves is the existence of a sufficiently wide phase of overlap. Strictly speaking, we are interested not so much in the phase width itself as a geometric value, but in the time interval when both valves are open. Without further explanation, it is clear that with a constant phase, with an increase in the rotational speed, the time decreases. It automatically follows from this that when the exhaust system is tuned to certain revolutions, one of the variable parameters will be the width of the overlap phase. The higher the tuning speed, the wider the phase is needed. From practice, we can say that an overlap phase of less than 70 degrees will not allow a noticeable effect, and the value for systems tuned to conventional 6000 rpm is 80 - 90 degrees.
Secondthe condition has already been defined. It is necessary to return the shock wave to the outlet valve. Moreover, in multi-cylinder engines, it is not at all necessary to return it to the cylinder that generated it. Moreover, it is advantageous to return it, or rather, to use it in the next cylinder in the order of operation. The fact is that the speed of propagation of shock waves in the exhaust pipes is the speed of sound. In order to return the shock wave to the exhaust valve of the same cylinder, say at 6000 rpm, the reflector must be positioned at a distance of approximately 3.3 meters. The distance traveled by the shock wave during two revolutions of the crankshaft at this frequency is 6.6 meters. This is the path to the reflector and back. The reflector can be, for example, a sharp multiple increase in the area of the pipe. The best way- cut of the pipe into the atmosphere. Or, conversely, a reduction in the cross-section in the form of a cone, a Laval nozzle, or, quite roughly, in the form of a washer. However, we agreed that we are not interested in various elements that reduce the cross section. Thus, tuned to 6000 rpm, the exhaust system of the proposed design for, for example, a four-cylinder engine will look like four pipes extending from the outlet ports of each cylinder, preferably straight, each 3.3 meters long. This design has a number of significant disadvantages. Firstly, it is unlikely that under the body of, for example, a Golf 4 meters long or even an Audi A6 4.8 meters long, it is possible to place such a system. Again, a muffler is still needed. Then we must introduce the ends of four pipes into a jar of a sufficiently large volume, with acoustic characteristics close to an open atmosphere. From this jar it is necessary to remove the gas outlet pipe, which must be equipped with a silencer.
In short, this type of system is not suitable for a car. Although in fairness it must be said that it is used on two-stroke four-cylinder motorcycle motors for circuit racing. For a two-stroke motor running at over 12,000 rpm, the pipe length is more than four times shorter to about 0.7 meters, which is quite reasonable even for a motorcycle.
Let's go back to our car engines. Cut geometric dimensions an exhaust system tuned to the same 6000 rpm, it is quite possible if we use a shock wave with the next cylinder in the order of operation. The release phase in it will come for a three-cylinder engine after 240 degrees of crankshaft rotation, for a four-cylinder engine - after 180 degrees, for a six-cylinder engine - after 120 degrees and for an eight-cylinder engine - after 90 degrees. decreases and for, for example, a four-cylinder engine will decrease by four times, which is 0.82 meters. The standard solution in this case is a well-known and desirable solution.<паук>... Its construction is simple. Four so-called primary pipes, which discharge gases from the cylinders, bending smoothly and approaching each other at a small angle, are connected into one secondary pipe having a cross-sectional area two to three times larger than one primary. The length from the exhaust valves to the junction is already known to us - for 6000 rpm about 820 mm. The work of such<паука>consists in the fact that the rarefaction jump following the shock wave, reaching the junction of all pipes, begins to propagate in the opposite direction into the other three pipes. In the next cylinder in the exhaust phase, the vacuum jump will do the work we need.
Here it must be said that the length of the secondary pipe also has a significant effect on the operation of the exhaust system. If the end of the secondary pipe is vented to atmosphere, then atmospheric pressure pulses will propagate in the secondary pipe against the impulses generated by the engine. The essence of adjusting the length of the secondary pipe is to avoid the simultaneous appearance of a vacuum pulse and a reverse atmospheric pressure pulse at the pipe junction. In practice, the length of the secondary pipe differs slightly from the length of the primary pipes. For systems that will have a further silencer, at the end of the secondary pipe, it is necessary to place the maximum volume and maximum cross-sectional area of a can with an absorbing coating inside. This bank should reproduce as best as possible the acoustic characteristics of an infinite amount of airspace. The elements of the exhaust system following this can, i.e. pipes and mufflers have no effect on the resonance properties of the exhaust system. We have already discussed their design, the effect on flow resistance, on the level and timbre of noise. The lower the overpressure they provide, the better.
So, we have already considered two options for constructing an exhaust system tuned to certain revolutions, which, by recharging the cylinders at resonance revolutions, increases the torque. These are four separate pipes for each cylinder and the so-called<паук> <четыре в один>... Mention should also be made of the option<два в один - два в один>or<два Y>, which is most often found in tuning cars, since it is easily assembled into standard bodies and does not differ too much in size and shape from the standard release. It is arranged quite simply. First, the pipes are connected in pairs from the first and fourth cylinders into one and the second and third into one, as cylinders equally spaced 180 degrees from each other along the crankshaft. The two formed pipes are also connected into one at a distance corresponding to the resonance frequency. The distance is measured from the valve along the centerline of the pipe. Paired primary pipes must be connected at a distance of one third of the total length. One of the frequently asked questions that have to be answered is what<паук>prefer. I must say right away that it is impossible to answer this question unequivocally. In some cases, a standard exhaust manifold with a standard standpipe works in exactly the same way. However, it is undoubtedly possible to compare the mentioned three constructions.
Here we must turn to such a concept as quality factor. Insofar as the tuned release is the essence of an oscillatory system, the resonant properties of which we use, it is clear that its quantitative characteristic - quality factor - may well be different. She is really different. The quality factor shows how many times the amplitude of the oscillations at the tuning frequency is greater than that far from it. The higher it is, the greater the pressure drop we can use, the better we will fill the cylinders and, accordingly, we will get an increase in torque. Since the quality factor is an energy characteristic, it is inextricably linked with the width of the resonant zone. Without going into details, we can say that if we get a big gain in torque, then only in a narrow rpm range for a high-quality system. And vice versa, if the range of revolutions, in which the improvement is achieved, is large, then the gain is insignificant, this is a low-quality system .. In Fig. 2, the vertical axis shows the pressure - the vacuum obtained in the area of the exhaust valve, and the horizontal axis - the engine revolutions. Curve 1 is typical for a high-Q system. In our case, these are four separate pipes, set at 6000 rpm.
First.Since the torque is proportional to the pressure drop, the number one high Q system will give the greatest gain. However, in a narrow rev range. A tuned engine with such a system will have a pronounced<подхват>in the resonance zone. And absolutely none at other speeds. The so-called single-mode or<самолетный>motor. Such an engine would most likely require a multi-stage transmission. In reality, such systems are not used in cars. The system of the second type has more<сглаженный>character, used mainly for circuit racing. The working rev range is much wider, the dips are less. But the increase in torque is also less. An engine tuned in this way is also not a gift, and there is no need to dream of elasticity. However, if the main thing is high speed while driving, then the transmission will be adjusted to this mode, and the pilot will master the control methods. The system of the third type is even smoother. The operating speed range is wide enough. The price to pay for this compliance is even less torque addition that can be obtained with the right setup. Such systems are used for rallying, in tuning for road cars... That is, for those cars that drive with frequent changes in driving modes. For which even torque is important over a wide rpm range.
Second.As always, there are no free gingerbread. At half the speed of the resonant frequency, the phase of the reflected wave will rotate 180 degrees, and instead of a vacuum jump in the overlap phase, a pressure wave will come to the exhaust valve, which will prevent blowing, that is, it will do the desired work the other way around. As a result, at half the speed, there will be a drop in torque, and the more we get at the top, the more we will lose at the bottom. And no adjustments to the engine management system can compensate for this loss. It remains only to put up with this fact and operate the motor in the range that can be recognized<рабочим>.
However, humanity has come up with several ways to combat this phenomenon. One of them is electronically controlled dampers near the outlet holes in the head. The essence of their work is that at a low multiple of the frequency, the damper partially blocks the exhaust channel, preventing the propagation of shock waves and thereby destroying the resonance that has become harmful. Expressed more precisely, reducing the Q factor many times. Reduction of the cross-section due to closed dampers by low revs not so important as a small amount of exhaust gas is generated. The second way is the use of so-called collectors ... Their job is to offer little resistance to flow when the manifold pressure is less than the valve, and to increase resistance when the situation is reversed. The third way is the misalignment of the holes in the head and the manifold. Manifold hole bigger size than in the head, coinciding along the upper edge with the hole in the head and not coinciding by about 1 - 2 mm along the bottom. The essence is the same as in the case of
cone. From head to pipe -<по шерсти>, back -<против шерсти>... The last two options cannot be considered exhaustive due to the fact that<по шерсти>still somewhat worse than smooth pipes. As a lyrical digression, I can say that hole mismatch is a standard simple solution for many serial motors, which for some reason many<тюнингаторы>considered a defect in line production.
Third.Consequence of the second. If we tune the exhaust system to a resonant frequency, for example 4000 rpm, then at 8000 rpm we get the above<провал>if the system turns out to be efficient at these speeds.
An important aspect when considering the operation of a tuned exhaust is the requirements for its design in terms of acoustic properties. First and foremost, there should be no other reflective elements in the system, which will generate additional resonant frequencies that scatter the shock wave energy across the spectrum. This means that inside the pipes there should be no abrupt changes in the cross-sectional area, corners protruding inward and connection elements. Bend radii should be as large as the motor layout in the vehicle allows. All distances along the centerline of the pipe from the valve to the connection should be the same as possible.
The second important circumstance is that the shock wave carries energy. The higher the energy, the more useful work we can get from it. Temperature is a measure of gas energy. Therefore, it is better to insulate all pipes up to the point of their connection. Typically, pipes are wrapped with heat-resistant, usually asbestos material and secured to the pipe using bandages or steel wire.
Now, after the processes taking place in the exhaust system have become clear, it is quite possible to move on to practical recommendations on setting up exhaust systems. I must say right away that in such work you cannot rely on your feelings and it is necessary<вооружиться>measuring system. It should be measured by a direct or indirect method at least two parameters - torque and engine speed. It is clear that the best instrument is a dynamometer for an engine. Usually they do the following. An experimental exhaust system is made for the engine prepared for testing. Since the motor is on the stand and there are no restrictions in the pipe configuration due to the missing body, the simplest forms are quite applicable. The experimental system should be comfortable and as flexible as possible for changing its composition and pipe lengths. Various types of telescopic inserts give a good and fast result, allowing you to change the lengths of the elements within reasonable limits. If you want to achieve from your power plant maximum parameters, you should be prepared to perform a significant amount of experimentation. Mathematical calculation and<попадание в яблочко>exclude from consideration the first time as an extremely unlikely event. It can be used like<приземление в заданном районе>... Some confidence that you are not far from the truth is given by experience and previous experiments with motors of similar characteristics, which have received good results.
Here, you probably need to stop and answer the question, and at what frequency should the exhaust system be tuned. To do this, you need to define a goal. Insofar as at the very beginning of the article we decided that we would achieve maximum power, then the best option in this sense is if we get an increase in torque on that part of the moment curve where the filling factor, and therefore the moment, begin to drop significantly due to the high rotation speed, i.e. the power will stop growing. Then a small increase in torque will give a significant gain in power. See fig. 3. In order to find out this frequency, it is necessary at least to have the torque curve of the engine with unadjusted exhaust, ie, for example, with a standard manifold open to the atmosphere. Of course, such experiments are very noisy and, excuse the harsh word, smelly, but necessary. Some hearing protection measures and good ventilation will provide the necessary data. Then, when we know the tuning frequency, we load the engine so that the rpm stabilizes at the desired point on the curve at 100% open throttle.
Now you can start experimenting with the different receiving pipes. The goal is to select such a front pipe or<паук>, or rather its length, in order to obtain an increase in torque at the desired frequency. When it hits the right point, the dynamometer will immediately respond with an increase in the measured force. The quickest result will be obtained by using telescopic tubes and changing the length with the engine running and loaded. Safety measures will be useful, since there is a possibility of burns, and an engine running at full load is dangerous in the sense of destruction. There are cases when, in an accident, fragments of a cylinder block pierced the body of a car and flew into the driver's cab. After the configuration has been found<паука>, you can start setting up the secondary pipe in the same way. As I already said, the influence of all other elements of the exhaust system is reduced to not losing what has already been achieved. Therefore, it is enough to attach pipes and mufflers that are planned to be installed in a car to the first two elements found and adjusted and make sure that the settings are preserved or have not significantly deteriorated. Then you can already start designing and manufacturing working system to fit the vehicle and fit in the body tunnel intended for it. I must say that the work is very large and it is unlikely that it can be done without special equipment. In addition, it should be borne in mind that many factors affect the settings of the exhaust system. Smokey Yunick, a well-known authority in the field of sports engines in the United States, believes that the exhaust system, intake and exhaust ports of the head, the shape of the combustion chamber, valve timing (camshaft), engine phasing, intake manifold, power system and ignition system are subject to joint tuning. He argues that any change in one of the named components necessarily entails a readjustment of all the others in order not to harm at worst, but at best to achieve greater motor efficiency. At a minimum, it is clear that in the overlap phase, when the tuned exhaust system is doing useful work, we are dealing with a through flow of gases from the intake to the exhaust manifold through the combustion chamber. The intake manifold, just like the exhaust system, can be considered an oscillating acoustic system with its resonant properties. Since the purpose of the tuning is to obtain the maximum pressure drop, the role of the intake manifold, or rather its geometry, is obvious. Its effect for motors with a wide phase of overlap may be less than from release due to lower energy, however, joint adjustment is absolutely necessary. For narrow-phase motors (read - serial), tuning the intake manifold is perhaps the only way to get resonant boost.
I would like to say a few words about the difference in tuning the injection and carburetor engines.
Firstly, the intake manifold design of an injection engine can be any, since we are not associated with design features carburetor, which means that the setting options are much wider.
Secondly, at multiple frequencies, the negative effect of the reverse pressure drop is significantly lower. The carburetor sprays fuel for any movement of air in the diffuser. Therefore, for multiple frequencies, an over-enrichment of the mixture is characteristic due to the fact that the same volume of air first moves through the carburetor from the combustion chamber to the filter, and then back in the same cycle. When electronic system injection, the amount of fuel can be strictly adjusted using the control program. Also, a programmable ignition timing can help reduce the harmful effects of backwash at these rpm, not to mention controlling those exhaust flaps that have already been mentioned.
And thirdly, the requirement for high-quality preparation of the mixture at low speeds dictates the need to use a narrowing section in the carburetor, known as a diffuser, which creates additional resistance to flow at high speeds.
For the sake of fairness, it must be said that horizontal twin carburetors Weber, Dellorto or Solex partially solve this problem, allowing each cylinder to give a pipe of the required length in order to adjust to the required speed, have a sufficiently large cross section, but still cannot fight over-enrichment. There is another trick to improve the efficiency of the exhaust system. It is used mainly in tuning, since with certain aesthetic inclinations of the designer it allows you to create a catchy appearance of the car. Somewhere, at least in photographs of American car enthusiasts, you have probably seen cars with rear bumper almost to the roof with the ends of the exhaust pipes. The idea behind this design is that when driving behind the rear edge of the car, a<воздушный мешок>, or rarefaction zone. If you find the place where the vacuum is maximum, and the end exhaust pipe placed at this point, we will lower the level of static pressure inside the exhaust system. Accordingly, the static pressure level at the outlet valve will drop by the same amount. Insofar as the filling ratio is higher, the lower the pressure at the outlet valve, this solution can be considered a good one.
In conclusion, I would like to say that despite the seeming simplicity, installing a different, different from the serial exhaust system, no matter how similar it may be to what is used in sports, does not guarantee your car additional horsepower. If you do not have the opportunity to make adjustments for your specific version of the motor, then the most reasonable way is that you buy a complete component for finalizing the motor from someone who has already performed these tests and knows the result in advance. The kit should likely include at least a camshaft, intake and exhaust manifolds, and a program for your ECM.
Good day, friends.
At the moment, the construction of another custom is nearing completion, and I was faced with an interesting problem - the exhaust.
The forward flow that was on the motorcycle, with its sound, caused profuse bleeding from the ears, contusion of squirrels in the forest, and with certain manipulations with the gas and clutch, it could raise the dead from the graves during rides near the cemetery. Who knows this problem, or is bored with the sound of a native muffler - please, under cat.
So, in a hardware store we need:
1) Furnace pipe, chrome-plated, stainless. You can have any other, in taste and color. I took the one that is cheaper :)
2) Perforated sheet. In my case, aluminum is 0.8 mm, size 500 * 250. If you can't find it, there are life hack oil filters from Kamaz-740. Inside the same perforated tube, only galvanized. They cost 80-100r, 2-3 pieces are needed for one muffler.
3) Steel 2mm, for the manufacture of flanges.
4) Minvata or its analogue, 1 sheet 50mm thick (the average price per pack is from 500r, I have left over from the repair)
5) Rivets, grinder discs, 2.5mm electrodes, etc.
I met the 560 rubles, in other cities the amount will vary, but I don't think that much.
We start by making a flute. Aluminum bends with bare hands, in my case, by winding a shovel around the handle :) 
Fixed with rivets.
Then we cut out the flanges. Cutting round parts with a grinder from the point of view of TB is not very correct, but I was naturally too lazy to go for a jigsaw blade. So if I haven't shown this method :) 
There was no compass at hand, but the diameter was needed 115mm, so the 115mm cut-off wheel became an excellent template. 
The pipes were again found in the garage. A small pipe is slightly reduced by cutting a pipe from a Zhiguli exhaust, a large one from a Gazelle exhaust. This part, again, you can make whatever you want - to taste and color. 
On the reverse side, we weld a side 20mm wide, under the rivets, so that everything is inserted flush: 
Like this: 
On the reverse side, we do the same. The flute stands in a spacer on the inlet and outlet branch pipes and does not need fixing, which is convenient in case of disassembly to replace the filler. 
Now the most important thing is to clog it with filler. The more it is, the better the sound damping, and the more densely it is clogged, the longer the service life. And yes, don't forget about protective equipment in the form of gloves and a respirator! 
That's all! It remains to rivet and come up with a beautiful clamp.
As for the flanges, while I'm thinking of polishing and covering with heat-resistant varnish, it will be seen in the future. 
I honestly tried to shoot a video of the sound, but while fiddling with the camera, the remaining gasoline ran out in the tank :)
So the final look and sound will be in the post about the whole motorcycle.
Summing up, we can summarize the following: analogues with the same characteristics cost from 5-6 thousand rubles, Chinese ones for 1.5-2 thousand rubles. terrible so much that it is unpleasant to hold even in the hands. I am silent about the characteristics.
