Today, we will break down how motorcycle exhaust systems work.
An exhaust is one of the most essential parts of any vehicle. Exhausts facilitate the removal of unnecessary waste gasses from the engine. Specifically, by-products of combustion that have no function in the engine are ejected via an exhaust system.
Not to mention, they sound fantastic! The design of an exhaust also greatly influences how your bike sounds and performs.
After having ridden and worked on motorcycles for the better part of 20 years, we have seen the inner workings of exhaust systems a hundred times over. We’ll help you understand the same exhaust system, from header pipe to muffler.
Keep reading for more info on how motorcycle exhausts work.
What Does An Exhaust System Do?
Put simply, an exhaust system facilitates the removal of unnecessary waste gasses that are produced in the engine during combustion. These gasses are extremely hot and toxic, so they need to be routed away from the rider.
In modern motorcycles, the full exhaust system also works to reduce emissions and regulate sound coming from the engine. All of this is done to comply with the emissions and noise regulations that the authorities have laid out.
So How Do Motorcycle Exhausts Work?
In years past, exhaust systems were little more than pipes that directed exhaust gasses away from the engine and into the atmosphere.
Nowadays, exhaust systems are a bit more complex and efficient. Not only do they direct waste gasses out of the engine, but they also work to reduce emissions and enhance the sound and performance of an engine.
Without getting into the minute details of how exhaust gasses are formed during combustion, let’s look at how these gasses are ejected from the engine.
As exhaust gasses make their way out of the cylinder, moving at around the speed of sound, they are directed into the header pipes. From there, they move towards the wider parts of an exhaust. The exhaust gasses start expanding at these wider sections, which creates the phenomenon known as backpressure. As the name suggests, this pressure wave travels back towards the engine, where the resulting pressure difference facilitates better efficiency.
Backpressure is one of the most important aspects of a motorcycle’s design. It helps the engine perform better while also aiding fuel mileage.
You might have heard the term ‘straight pipe’ regarding motorcycle exhausts. This refers to an exhaust system with no cross-sectional changes in its design.
Straight-piping reduces the effort needed to push exhaust gasses out of the engine, resulting in higher power output. However, this same design will result in worse mileage as well.
Most every modern motorcycle exhaust design features a component known as the catalytic converter. This part of the exhaust is tasked with converting the highly toxic and pollutant exhaust gasses into less harmful gasses before they are ejected into the atmosphere.
The catalytic converter itself is made from a combination of various metals that act as catalysts. These include platinum, rhodium, and palladium. The exhaust gasses from your motorcycle’s engine react with these catalysts in two stages.
The first stage converts harmful nitrogen oxides into less pollutant nitrogen and oxygen. While the oxygen is allowed to move on, nitrogen is trapped at the catalytic converter.
The second stage manages unburned hydrocarbons, carbon monoxide, and other harmful gasses.
The last component is your exhaust system’s muffler. The exact shape and size of the muffler, and various internal components such as baffles and butterfly valves that it uses, all govern how loud the exhaust is.
How Does Exhaust Affect Motorcycle Performance?
As mentioned above, an exhaust is integral to the performance of your motorcycle. Different exhaust setups can dramatically change how your bike sounds and how much power the engine generates and how that power is delivered.
Different exhaust systems will produce different amounts of backpressure. Along with the engine’s efficiency, back pressure also plays a massive role in the performance.
Aftermarket exhaust systems add power to the engine by allowing a higher volume of exhaust gasses to be ejected in the same amount of time.
One of the most popular methods of adding power to a motorcycle is swapping out the restrictive stock exhaust for a higher performance pipe.
However, if you swap out one exhaust for another, you will have to retune the engine to match the freer flow design. Otherwise, you will end up losing power instead of gaining any. Tuning an engine refers to setting up the air-fuel ratio so that the engine performs optimally.
You can tune an engine via the carburetor, or the ECU in fuel-injected motorcycles.
Can You Put Any Exhaust On A Motorcycle?
Not exactly. While all exhaust systems work on the same basic principle, different engines will have varying requirements for the exact diameter of the pipe.
Furthermore, just because it fits physically doesn’t mean it will work well with the bike. Different engines will need different levels of exhaust flow to work efficiently.
In most cases, aftermarket exhaust systems are tailored to the bike and its specific requirements. There is a fair bit of cross-compatibility, but not every exhaust will fit every bike. And even if it does, there is no guarantee that you are getting the best performance out of it.
Can You Run A Motorcycle Without An Exhaust?
It depends. If by ‘exhaust’, you mean the muffler, then yes, you can run the motorcycle without the muffler. The bike will be a lot louder. You might be breaking a couple of noise pollution laws, but functionally, it’s possible.
However, you might get slightly worse performance if the bike’s air-fuel ratio also accounts for the muffler—nothing you can’t solve with a tune.
If by ‘exhaust,’ you mean the entire exhaust system, including the headers and exhaust manifold, then no, you can’t run the bike without an exhaust. Doing so could damage the engine beyond repair.
This is because the exhaust is an essential component in the combustion process. It provides back pressure which is all but necessary for proper combustion and power delivery.
You should now have a pretty rudimentary understanding of how motorcycle exhausts work. The exhaust system your bike uses comprises several individual components, each of which has its own function.
Some exhaust components are legally required, such as the muffler and catalytic converter. Others, such as the exhaust manifold, are necessary for proper combustion.
But at the end of the day, each of these components plays a role in how your bike performs, sounds, and rides.