Exhaust is one of the most important parts of the motorcycle. It is a passage for exhaust gases generated in the engine combustion chamber to move out of the motorcycle.
So, what does a motorcycle exhaust do? A motorcycle exhaust primarily takes away the exhaust gas coming from the engine and releases it to the outside atmosphere. It also makes your motorcycle quieter, converts the harmful gases into less harmful and lastly, improves motorcycle performance.
Exhausts were discovered in the late 1800s and back then they were used only to put out the burnt gas from the motorcycle.
As time passed, engineers worked on exhausts so that they can do more than just redirecting the harmful gas away from the bikes. Thus, exhausts underwent drastic modifications to arrive at their present look and design.
Types Of Exhausts
Exhausts come in different varieties that vary in their functions.
Based on the type of exhaust you choose for your motorcycle, the exhaust weight, performance and noise varies.
Here are the different types of exhausts and their functions.
#1: Straight Or Drag Pipe
Straight or drag pipe exhausts are the most common exhausts that are found commonly in motorcycles.
These exhausts have a single header and a single exhaust. The single pipe acts as the sole passage for exhaust gases to escape out from the engine chamber to the outside atmosphere.
#2: Dual Exhaust
Dual exhausts are usually found in heavy motorcycles like Harleys.
In dual exhaust, the two cylinders are attached to two different exhausts. As a result, the exhaust gases don’t have to rush through a single exhaust, thus improving the motorcycle mileage and performance.
On the flip side, dual exhausts increase the weight of the motorcycle.
#3: Two Into One Exhaust
Two into one exhausts have two headers connecting to a single exhaust. These exhausts are lighter than a dual exhaust.
In addition, they also increase the performance by effectively taking away the back-pressure.
#4: Four Into Two Exhaust
In four into two exhausts, four headers are connected to two cylinders. These four headers then split into two exhausts.
These types of exhausts are heavier but some motorcycles perform better with these exhausts.
#5: Four Into One Exhaust
Four into one exhausts have four headers connecting to four cylinders.
These four header pipes then merge into a single pipe before connecting to the collector. These exhausts greatly reduce the weight and are preferred in some motorcycles to increase performance.
Motorcycle Exhaust Parts
Before understanding how the exhaust performs all of those functions let’s dig into different exhaust parts first.
The exhaust gas from the engine enters these pipes. These pipes move along the engine and release those gases into the collector. It also helps in reducing the backpressure.
Collects the gas from the header pipes. Here the conversion of harmful gases and noise reduction (to some extent) happens.
These are housed inside the collectors and inside the connector pipes that connect the header and the collector in a Four into One (or in a Four into Two) exhaust. They convert harmful gases like CO into less harmful CO2.
These are located near the collector. They sense the amount of oxygen present in the exhaust and send feedback to the engine whether it is using more or less fuel.
Just before the muffler, there is a servo-controlled valve that regulates the backpressure as well as noise.
Bafflers or Silencers
These are components that regulate the noise and backpressure. They are housed inside the muffler.
Now that we have a brief idea about different exhaust parts, here is how exhausts work and keep the motorcycles in healthy conditions. We go through the mechanism part by part here.
- In a four-stroke engine, high-pressure exhaust gas enters the header pipe during the exhaust stroke.
- This gas moves along the slender pipe and enters the broader collector.
- In the collectors, two things happen- catalytic conversion of harmful gases and noise reduction.
- In the collector, the gas expands because it has entered a broader pipe.
- Once it expands, it sends a negative wave pressure back to the exhaust valve.
- During this stage, the exhaust valve begins to close and the intake valve begins to open. Because of this, both the valves will be slightly open and this is called the Overlap stage.
- Exactly during the overlap stage, the negative wave pressure enters the exhaust valve that helps in pulling any residue gas present in the exhaust valve.
- The pressure is so much that it also pulls the fuel and air through the inlet valve even before the inlet stroke begins.
- The gas passes through a catalytic converter in the collector (some exhausts have a catalytic converter placed in the connecting pipe that connects the header to the collector as well).
- The harmful gases react with the catalytic converter and get converted into CO2.
- In some exhaust, there will be an Oxygen sensor. This will detect the level of O2 present in the exhaust gas and if the level is low it will make the engine burn less fuel and if it is very high it makes the engine burn more fuel.
- From here the exhaust gas moves through a butterfly valve that regulates the backpressure and sometimes it is also used to regulate the noise.
Bafflers or Silencers
- Then the exhaust gas enters the muffler where the baffler resides.
- Baffler reduces the noise further as the gas passes through the network of porous pipes.
Functions Of A Motorcycle Exhaust
Since we have already touched upon the uses, parts and explained the mechanism of of the exhausts, here is the recap on the functions of a motorcycle exhaust.
- Primarily, a motorcycle exhaust takes away the exhaust gas coming from the engine and releases it to the outside atmosphere.
- It also makes the motorcycle quieter
- Converts the harmful gases into less harmful
- And lastly, improves motorcycle performance.
When it comes to performance, backpressure is a very important thing to consider.
In the exhaust system, the Butterfly Valve plays a major role in regulating the back-pressure and hence the bike performance. It is a new addition to the OE exhaust system.
Many people replace the OE exhaust with an Aftermarket exhaust for the following reasons.
- Better performance
- Better look
- Better sound
- Better efficiency
Yeah, aftermarket exhausts can give you all that. BUT, in most countries they are illegal.
This is because aftermarket exhausts are found to cause high air pollution and noise pollution.
The OE or factory exhaust can’t give you all those because they have to follow emission guidelines provided by the government.
As a result, these exhausts have to put a limit on the dB and a check on harmful gases. However, after market exhausts do not guarantee to comply with these stringent emission guidelines.
How To Choose An Exhaust
Nowadays the OE exhausts also provide better performance along with following all the guidelines from the government.
Still, aftermarket exhausts are popular because people like the loud noise and the look aftermarket exhausts give.
But to install an aftermarket exhaust, you need to get approval from the local regulatory body.
That’s why if you want to go for an aftermarket exhaust for better performance, you should think again. In some countries, installing after market exhausts are downright illegal.
If it is just about changing the exhaust looks, you can consider only changing the mufflers. That should work just fine.
Despite all these obstacles. if you still want to go for an after market exhaust for your motorcycle, here are few things to consider.
- Configuration: A Four into One exhaust is preferred because it can give you better performance along with look and sound – provided your motorcycle is on the heavier side and can hold such a large exhaust.
- Material: If you have a budget you can go for the lightweight and highly efficient titanium exhausts. But, if you are on a budget you can choose a stainless steel exhaust that is both cost-effective and durable. The aluminium exhausts can come in handy if you are living in dry weather. There are carbon fibre exhausts that are costly but they are durable and conduct heat slowly so they don’t get hot quickly. Then there is chrome which gives the look that you want along with longevity.
- Fuel management: If you are replacing your factory exhaust system with an aftermarket one then you should change fuel management. Without fuel management change your aftermarket exhaust is just a waste of money. For that, you’ll need a fuel controller (for fuel-injected bikes) or jet kits (for bikes with carburetors)
How To Take Care Of Motorcycle Exhausts
Exhausts get exposed to high temperatures of the exhaust gas, external factors like dust, water etc, so they do get decolourized and that’s natural. But if you want to avoid that you can by using double-wall pipes, a coat of heat-protective shields or fibreglass tape etc.
Along with this checking, the health of your exhaust system is also equally important, because usually, people neglect to check on their exhaust system thinking that they are there to just throw away the exhaust gas. But if the exhaust system is not in the condition it directly affects the performance of your motorcycle.
Exhausts are vital parts of the motorcycle. It not only keeps the exhaust gas away but also cleans the exhaust of harmful gases, increases the performance of the motorcycle and decreases the noise. Overall it protects the motorcycle, the rider and the environment from the exhaust gas and the noise that is produced.
Nowadays the factory exhausts also consider the performance while controlling the noise and the type of gas that goes out. So, purchase an aftermarket exhaust system only for their looks and sound. But make sure that you are not breaking any laws.