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Who else wants to know about the differences between long vs short exhaust pipes?
The best motorcycle exhaust length is something that many riders find confusing.
Well, if you think that simply by changing the exhaust system length you can add more power or sound to your fire-breathing beast, think again.
Motorcycle exhaust systems are carefully calibrated to ensure the best performance. The engineers in design have already done all the hard work
And believe me when I say this- it’s not so simple.
You need to take into account factors like engine rpm, exhaust gas velocity and temperature, valve timings, and more.
Still, if you need to make a choice between the two types, here are the basic differences between the two.
- Firstly, it’s about aesthetics. You may choose the exhaust system length based on the style you prefer. I prefer the traditional longer style in shiny chrome. But you may like the short and sporty design.
- In terms of performance, the difference isn’t much. A short exhaust will increase the torque at high RPM while a long exhaust will increase the low RPM torque. But both increments are minimal.
- Long exhausts are usually quieter. Want your beast to emit a higher-pitched roar? Try short exhausts. However, they might be illegal in your area. But keep in mind, the sound output also depends on the design of the exhaust baffles.
Let me guess…
You’re still not sure about the best choice.
Not to worry.
To help you understand better, we will dig a little deeper and find out more about short exhaust vs long exhaust motorcycles.
The Details of an Exhaust Assembly
If you don’t know this already, the exhaust assembly has multiple parts that are carefully integrated for the best performance. I also touched on the various components of the exhaust system in my post about how hot motorcycle exhausts get.
To start with, let’s take a look at the various sections of a typical exhaust pipe and how the different zones impact engine performance.
- The first section is the head pipe which connects to the engine exhaust. The design of the head pipe is critical and the manufacturing process is expensive. Its design impacts the overall performance as well as the low to mid-rpm power output. Larger head pipes deliver more power at the bottom end.
- After the head pipe lies the divergent first cone of the exhaust system. The volume and taper angle of the cone are carefully calculated as it influences the engine’s peak power delivery. A steep taper angle will result in high peak power, whereas a smooth taper will produce a gradual power delivery.
- The belly is a cylindrical portion that connects the convergent and divergent cones in the exhaust assembly. The length and volume of this portion are adjusted to match the performance of the head pipe.
- The final cone controls the power output delivered after the peak power. A steep taper angle will give less overrun and a gentle taper will deliver more overrun.
- The end part of the exhaust is termed the stinger. Long stingers help in boosting the mid-range power to some extent. If the stinger diameter is kept large, bottom end power is boosted, but the peak power output suffers.
The fact is, the “bigger is better” approach doesn’t work for exhaust assemblies. It’s not just about looking good but about optimizing the overall performance.
Now, some research has indicated that varying the exhaust pipe length and valve timing didn’t produce any significant change in engine volumetric efficiency. However, varying the exhaust pipe diameter can have more effect on the torque output.
Short vs. Long Exhaust Performance
When it comes to picking an aftermarket exhaust, there are two options. You can replace only the mufflers by choosing a slip-on system. It’s less expensive and a good choice if you are looking for a throaty rumble.
Replacing the full exhaust system is more complicated and needs a proper modification plan.
Get this: complete modification of the bike’s exhaust system isn’t cosmetic. It will impact the overall performance of the bike.
The overall length of the pipe influences the process of exhaust wave scavenging and the engine’s ability to exhaust the burnt gases. The pipe length also affects the positive and negative pressures created at the engine cylinders.
Based on the engine rpm, the manufacturer can choose a longer pipe that will better regulate combustion gases. On the other hand, if the pipe is too long, the exhaust backpressure will get reduced and the performance will come down.
Keep in mind, the diameter of the pipe also determines the overall exhaust pipe volume. Smaller pipes can create more backpressure on the engine piston and reduce pumping efficiency. More backpressure also leads to increased fuel consumption and higher emissions.
Let’s keep it simple. Is backpressure good or bad?
Basically, engineers try to adjust the length and diameter of the exhaust pipe to raise exhaust velocity and balance the backpressure to match the engine rpm.
(Reminds me of a funny story about striking a balance in life. Some other time, eh.)
Do you see where we’re going with this?
When you install a new exhaust, the engine needs to be tuned to ensure optimized performance. Miss that step and you’re likely to get lower performance.
Not to forget, when you choose a short exhaust, you are lowering the weight of the motorcycle. And when it comes to performance, every ounce matters. That makes tuning your engine even more important.
If you’re looking for long vs short exhaust choosing tips, know that each system has its own pros and cons. To be honest, there’s no exact formula that will pinpoint a precise length for the exhaust system without compromising performance.
For casual commuters, the performance difference between long and short exhausts isn’t much. As long as you tune the engine correctly, feel free to choose whatever looks better to you.
Frequently Asked Questions
Does the length of the exhaust pipe affect performance?
It surely does. Simply changing the length of the exhaust pipe isn’t the right thing to do. You need to match the pipe dimensions with the engine specifications for optimum performance.
Does exhaust pipe length affect sound output?
In general, shorter exhaust pipes are louder. But the sound output also depends on the baffle design. So, a longer pipe can be loud too.
What happens if the exhaust pipe is too small?
It will generate too much backpressure which will restrict the exhaust gases from leaving the engine. That will lead to lower engine performance.