If you want a much louder sound from your motorcycle, then straight piping is an option – but should you do it? What are the cons of straight piping? Will you lose horsepower or even damage your motorcycle engine?
Those are the questions I will discuss in this article. I will go into the details – beginning with what straight piping in a motorcycle even is and why they could be bad for you.
If you are busy and want the quick answer – straight piping a motorcycle will not damage the engine. However, you could lose some horsepower because exhaust scavenging is reduced and emission from your motorcycles will be massive – making it illegal.
If that’s too much to digest, don’t worry. Let’s go through all of them right now.
What’s a Straight Pipe On a Motorcycle?
Straight piping a motorcycle means removing the muffler and catalytic converter from the exhaust of your motorcycle. This means your exhaust will be extremely short – consisting only of the exhaust header.
See this image below. That’s a motorcycle with a straight pipe. Straight piping does not literally mean replacing your exhaust with a ‘straight’ pipe. The shape of the pipe doesn’t matter here!
Straight Piping Motorcycle Vs Car
Straight piping in a motorcycle and in a car is a little different. The concept is the same – it’s about removing the catalytic converter and muffler from the exhaust system. However, the way to do it and the desired result is a bit different.
A car’s exhaust system is much larger than a motorcycle – it contains a standalone catalytic converter (CAT) and muffler. To straight pipe a car’s exhaust, you need to remove the CAT and muffler and then replace it with a steel hollow pipe.
A motorcycle’s exhaust system, on the other hand, is much smaller – the CAT and muffler are combined as a single unit. To straight pipe a motorcycle, you just remove the muffler from the exhaust – no replacement required.
A car enthusiast might want to straight pipe to get louder sound and more horsepower. Most motorcyclists look to straight-pipe only to get louder sound.
Straight piping a motorcycle actually causes it to lose horsepower! I will cover more about this later in the article.
It’s important to understand this difference, because as you read online forums or articles, most times they are talking about straight piping a car and that could get you confused!
Will Straight Pipe Ruin Your Motorcycle Engine?
Straight pipe will not ruin your motorcycle engine. The motorcycle engine is not exposed by a straight pipe and does not get impacted enough to the point that it will break or burn.
The engine aside, there are many things that a straight pipe could impact such as horsepower, backpressure, scavenging and exposed O2 sensor.
All these are related to the horsepower output. So let’s touch on this topic now.
Will Straight Pipe Make Your Motorcycle Lose Power?
Straight piping a motorcycle will make you lose horsepower – around 5-10 horsepower. This is because a straight pipe will likely make your engine run lean.
Why lean? Good question, let me get into the details by first explaining how a motorcycle engine generates power.
A motorcycle engine generates power by mixing fuel and air to create combustion in the combustion chamber.
This combustion is an explosion that generates power and exhaust gases. Thest gases must leave quickly to give room for fresh air for the next combustion.
The fuel and air mixture must be perfect. Too much air will make your engine run lean. Which means there’s not enough fuel required to create the perfect combustion – causing you to lose horsepower.
Too much fuel will make your engine run rich. Which means there’s not enough air to burn off the fuel – causing excess fuel to leave the combustion chamber and reduce your fuel efficiency.
By having a straight pipe, you will have removed all the restrictions from the CAT and muffler – allowing your exhaust gases to flow and escape even quicker.
Not to mention your exhaust is much shorter now – speeding up the time it takes for your exhaust gases to leave even more.
Now that your exhaust gases are leaving the combustion chamber rapidly, more space is made available for fresh air to enter.
Without tuning, this results in your engine running lean because the amount of air significantly increases but the injected fuel remains the same.
And what happens when your engine runs lean? That’s right, not enough fuel to create the perfect combustion – which then reduces horsepower!
Motorcycles Need Backpressure Myth
There’s a common misconception where a motorcycle needs back pressure and when straight piping, you would reduce that back pressure – causing a drop in horsepower.
This is incorrect. A motorcycle engine does not need back pressure to function. Reducing back pressure is always good for a combustion engine. This misconception happens because people are confusing exhaust scavenging with exhaust back pressure.
As discussed above, straight piping may cause you to lose some horsepower because it makes your engine run lean. Not because it reduces exhaust back pressure.
Let me quickly touch with you on the difference between back pressure and scavenging. This should clear up things for you the next time you are lurking around on online forums.
Motorcycle: What’s Exhaust Backpressure?
Exhaust back pressure is the air pressure from the exhaust system and back. This is never desirable – the lower the back pressure the better.
Do you still remember how a motorcycle engine generates power? It uses a mixture of air and fuel to generate combustion in the combustion chamber.
Combustion in turn generates toxic exhaust gases that must leave the chamber as quickly as possible. The quicker exhaust gases leave, the more room is available for fresh air to enter the combustion chamber for the next cycle.
With some high school science, we know that air particles (like exhaust gases) like to travel from high pressure areas to low pressure. This also applies in a motorcycle engine.
Exhaust gases leave the combustion chamber into the exhaust system because there’s a lower air pressure in the exhaust system (back pressure) than the combustion chamber.
Which means, the more you reduce air pressure in the exhaust system (back pressure), the more likely these exhaust gases want to escape from the combustion chamber into the exhaust system.
You should always look to reduce back pressure in your engine. Now that back pressure is clear, let’s talk about exhaust scavenging. It’s a little more complicated – which is why people have misconceptions.
Motorcycle: What’s Exhaust Scavenging?
Exhaust scavenging is a natural effect that helps increase the speed of exhaust flow. When exhaust gases escape the combustion chamber, they move in high speed pulses.
These pulses push forward air particles on their way – causing a high air pressure area in front of them and low pressure area behind them.
The gases in the low pressure area naturally get pulled forward into the higher pressure areas – providing you with an increased exhaust velocity. This natural effect is known as exhaust scavenging.
You always want more exhaust scavenging and lower back pressure. Don’t mix the two! I will write another article to dive deeper into exhaust scavenging and motorcycle engines. So stay tuned!
Pros Of Straight Piping Motorcycle
To be honest, there are not many concrete pros to running a straight pipe – they are all subjective. Here we go.
- Louder and aggressive sound. Without the muffler in place, your motorcycles will be extremely loud – especially during a cold start. There are plenty of before and after videos on YouTube. I recommend checking them out to make sure you like it!
- Exhaust looks cooler. This is subjective. Some riders think that the shorter exhaust from straight piping looks cool and unique. If you are one of them, this point is for you.
Cons Of Straight Piping Motorcycle
Straight piping a motorcycle has many more cons when compared to the pros. Make sure you are fine with all these points before you decide to do it!
- Extremely loud. Without the muffler, your motorcycle will become extremely loud and even deafening. Many people (especially your neighbors) will not enjoy it. These loud sounds tend to be cool initially but become annoying soon after.
- Increased emission. Without the CAT, your motorcycle will be letting off toxic exhaust gases in the surrounding. I hope you are wearing a helmet at all times. Otherwise, some of these gases can get inside your lungs and become dangerous.
- Mostly illegal. This depends on where you live. But in most areas, straight piping is illegal. Both the noise and emission is too much for street use.
- Decreased horsepower. Without tuning, straight piping makes your engine run lean and cause you to lose horsepower.
- Exposed O2 sensor. With straight pipes, the O2 sensor could be exposed into the atmosphere. This causes it to have inaccurate reading and mess up the fuel injection in your engine.
Straight Piping Motorcycle: My Recommendation
I don’t recommend to straight pipe your motorcycles at all. The cons are too many and they all outweigh the pros.
If you are serious about having a better performance or sound, then you should look into installing an aftermarket exhaust for your motorcycle.
Do a lot of research before you pick one. Go into different forums and watch YouTube videos to listen to the before and after sound.
This way you can be sure to improve your motorcycle performance and sound – while still being legal.