Does straight pipe exhaust add horsepower?

By July 5, 2020September 28th, 2020Does It Add HP?, Performance Modification

So you heard that a straight pipe exhaust can improve car performance and you want to know why. You begin googling and can’t really understand the explanations at all. Straight pipe exhaust reduces back pressure and thus increases performance. Okay… what did I just read? Back pressure, mufflers, cats, etc. – what do they even mean?! This was me when I started out. Let me explain straight pipe exhaust in a much simpler way.

To answer the question – Straight pipe exhaust could increase horsepower and torque. Straight piping removes mufflers, catalytic converters and resonators from your exhaust – allowing a much better exhaust flow for the after combustion gasses to leave. The better these harmful gasses leave, the more air and fuel can be injected into the combustion chamber, allowing for more performance. 

Still too much to digest? Let’s break it down into multiple components. Read on.

What’s The Use of an Exhaust System?

Every car is equipped with an exhaust system. To understand about straight exhaust pipes, we must first understand what an exhaust system is. An exhaust system has 3 main functions:

 

Allow toxic gases to leave

When your car creates combustion to generate power, toxic gases such as Carbon Monoxide (MO) and Nitrogen Oxide (NOx) are produced. These gases must exit the combustion chamber to make room for the next combustion. Otherwise, your car engine will not be able to combust and generate as much power as it could – leading to a decreased in performance and horrible fuel consumption. 

This is where an exhaust system comes into place. An exhaust system allows these toxic gases to flow out from your car through the tailpipe. 

Image of gas coming out of exhaust pipe

 

Reduce toxic gases 

Now that you know toxic gases need to leave your car into the outside world, you might be wondering – won’t the pollution be crazy then?! It doesn’t make sense for us to allow toxic gases to escape into the air we breathe in. That’s not all – these toxic gases like Carbon Monoxide also destroys the earth’s Ozone layer and causes acidic rain!

But relax, this is why an exhaust system is also equipped with a catalytic converter – AKA ‘cat’. Without going into too much science, a cat converts the toxic gases into non toxic ones. This means:

  • Carbon Monoxide (CO) is converted into Carbon Dioxide (CO2) 
  • Nitrogen Oxide (NOx)  is converted into Nitrogen (N) and Water vapour

Thus, when the toxic gases flow through your car’s exhaust system, they are converted into non toxic gases, before they are released into the environment. 

 

Reduce Noise

When your engine creates combustion to deliver power, it also generates a loud noise. Along with the toxic gases, these sound vibrations will also travel through the exhaust system. Thankfully, a stock exhaust system is always equipped with a muffler – which reduces noise from combustion significantly. 

What is a Catalytic Converter (CAT)?

In this section I cover the workings of a CAT. You may skip this section and go for the explanation of straight exhaust pipe immediately. 

Remember that a catalytic converter converts toxic gases produced by combustion into non-toxic gases. But how does it even work? 

  • A catalytic converter is made of ceramic and consists of Platinum, Palladium and Rhodium
  • Platinum and Rhodium can pull Oxygen molecules from Nitrogen Oxide (toxic) which results in Oxygen and Nitrogen (these are safe!) 
  • Platinum and Palladium can also bind the Oxygen into Carbon Monoxide (toxic) which results in Carbon Dioxide (safe!) 

Simple enough? 😉 

Side info: Do you see why there are people stealing catalytic converters? They consist of these rare metals that could be sold for a high price!

What is a Muffler?

In this section I cover the workings of a Muffler. You may skip this section and go for the explanation of straight exhaust pipe immediately. 

I mentioned that a combustion produces lots of noise and a muffler is used to significantly reduce these noises. But how does a muffler work? 

  • A muffler’s main job is to reverse the direction of sound waves so they hit into each other and cancel out.
  • A muffler’s internal consist of sophisticated channels, holes and tubes – designed to create walls that cause the sound waves to bounce and reverse into each other.

Both exhaust gases and sound waves pass through the muffler. However, only sound waves get bounced and reversed into each other. The exhaust gases simply have to flow through it.

Image of the internals of a muffler

Straight Exhaust Pipe

A straight exhaust pipe has nothing to do with it being straight. Just because an exhaust pipe is straight, doesn’t mean it’s a straight exhaust pipe. Well technically yes… But no! 

A straight exhaust pipe is an exhaust that does not equip any muffler or catalytic converter. The exhaust gas from combustion goes directly from the exhaust header to outside the car – nothing in between. The idea is to remove any components which could restrict the flow of the exhaust gas – allowing the exhaust gas to exit the car as easily and quickly as possible.

More exhaust gas exiting the gas chamber means that more fresh air can flow inside for the next combustion. If exhaust gas is trapped inside the combustion chamber, the next combustion will have less air and thus, generating less power. Adding a catalytic converter and muffler into the exhaust system has its benefits like I covered above. However, this means the exhaust gas will take much longer to exit the car – this is referred to as a back pressure.  With the muffler and catalytic converter gone, the exhaust gas can swiftly exit the car. Which means more air can now flow into the emptied combustion chamber – allowing for an optimal combustion and power. So to recap here again – yes, a straight exhaust pipe has the potential to increase horsepower. 

Image of straight pipe exhaust

Pros of Straight Exhaust Pipe

Improved car performance

As we have already discussed, a straight exhaust pipe does not equip any muffler or catalytic converter. This means the exhaust gas can exit the combustion chamber easily into the outside world. Having this, more air can enter the combustion chamber – which could generate more combustion and power for the car. 

 

Better fuel consumption

This is related to the above point. More air entering the combustion chamber means that the chances of injected fuel completely being utilized will be higher. Without enough air, not all injected fuel will combust – causing it to exit along with the exhaust gas to the outside environment. What a waste!

 

Louder engine sound

Without a muffler in place, noise created by the combustion will not be silenced. This means your car will significantly be louder – especially when you press the paddle. This point could either be a pro or con – depending on the driver. You will either absolutely hate it or love it.

 

Which muffler is your car right now?

Reduced vehicle weight

You will only care about this if you are a complete performance junkie… By removing the catalytic converter and muffler, the weight of the car will also be reduced. Lighter car means that it has the potential to travel faster and save fuel. 

Cons of Straight Exhaust Pipe

Horrible Emission

With the catalytic converter removed, all the toxic gases from combustion will flow straight out. You will most definitely fail every emission test there is. Aside from the failed emission test, you will also be taking a big part in destroying the environment. Ouch. Please consider this heavily before you make the decision 😉

Louder engine sound

Again, this can be a pro or a con – depending on you. I want to stress this point again. The engine sound will significantly be louder – sometimes deafening. Even if you like it, the sound can get boring pretty quickly if you are equipping a straight exhaust pipe on a street / daily car. Also, the government rules and regulation of your area might not allow you to drive without a muffler at all. Check these rules out before you decide on equipping a straight exhaust pipe. 

 

Hard to resell

Should you decide to sell your car that’s equipped with a straight exhaust pipe, it could be a challenge. 

  • A big majority (like 99%) of regular drivers who are not interested in performance will not appreciate the engine sound
  • Most people would not risk getting fine by the failed emission test or by the loud engine noise
  • Your car might even depreciate in value because of equipping the straight exhaust pipe. Even when you paid extra cash to equip these bad boys

Should I Install Straight Exhaust Pipe?

From my personal opinion, I don’t think you should install a straight exhaust pipe on your daily street car. The cons far outweigh the pros. It gets even worse when you are playing around with rules and regulations. I suggest that you only consider installing an exhaust pipe if you have a hobby on racing. Install only your race cars that you will use occasionally on the race track.

If you like a louder engine sound. Look into installing a cold air intake or a performance muffler instead. They are significantly cheaper to install and do not cause emission  Check this article where I talk about cold air intake. And this article where I discuss the best performance muffler to look for.

Ifandi S.

Ifandi S.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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