Does Downpipe Make A Car Louder?

By September 22, 2020October 6th, 2020Common Questions, Downpipe

Aftermarket downpipe definitely makes a car louder and sound more aggressive. This is because aftermarket downpipes are louder than stock and they reduce the backpressure in exhaust. Allowing sound waves to travel smoothly without collision. 

Downpipe comes in two types: catted and catless. Which of these produce more sound for your car? Keep on reading and I will cover this. 🙂 Starting with what a downpipe is all about.

Recap: What’s Turbocharger And How Does It Work?

To understand downpipe, we must first understand turbocharger. This section is a recap for the beginner enthusiasts. If you are a pro, just skip the recaps 🙂

That said – turbocharger AKA turbo, is a performance mod that could increase horsepower significantly. To generate power, your car creates combustion in the combustion chamber. Long story short, combustion is created by using fuel and air. Combustion delivers power and creates exhaust gases as byproducts.

So far so good right? If you want more horsepower, you need bigger combustion – which means more fuel and air. Getting more fuel in the combustion chamber is easy – just inject more. 

Getting more air into the combustion chamber is the hard part. Every performance mod like turbo, cold air intake and nitrous work to achieve this

Turbo is an air compressor that sucks air from the surrounding, compresses it and delivers it directly into the combustion chamber. Suddenly, the amount of air in the combustion chamber is increased. All that’s left is to inject more fuel for a MONSTER  combustion.

The beautiful thing about turbo is that it’s self powered – no fuel is consumed to power the air compressor. Instead, turbo has a turbine which gets spun by exhausts gases coming out from the combustion chamber. 

Tubo can deliver even more air to the combustion chamber if the flow of exhaust gases is faster (or more exhaust gas). After flowing through the turbine in turbo, exhaust gases continue to flow through the exhaust pipe and exit the car. 

I have an article comparing Turbocharger and Supercharger. Check it out if you want to know more about turbos.

Image of turbocharger
Exhaust gases flow through here and drive the turbine in the turbo
Air is sucked and compressed
Compressed air is delivered to combustion chamber

Recap: What’s a Downpipe And What Does It Do?

I just mentioned that after exhaust gases flow through the turbine in turbocharger, they continue to flow through the exhaust pipe and exit the car.

How exactly does exhaust gases travel in the car anyway? Let me break down the complete journey of exhaust gases for you:

  1. Exhaust gases generated by combustion combustion chamber.
  2. Exhaust gases leave the combustion chamber through the exhaust header.
  3. Exhaust gases enter the turbocharger’s turbine through up-pipe.
  4. Exhaust gases leave the turbocharger through down-pipe into the exhaust pipe.
  5. Exhaust gases travel through the rest of the exhaust pipe, go through the muffler and exit the car.

Did you catch what the downpipe does? If you don’t, a downpipe directs exhaust gases from the turbocharger into the exhaust pipe where they eventually exit the car.

downpipe connected to turbo
Downpipe connected to turbo outlet
There’s no catalytic converter here. This is a catless downpipe
Exhaust gases exit downpipe to enter the rest of exhaust pipe

Recap: Why Install Aftermarket Downpipe?

Aftermarket downpipes have a bigger diameter. This means exhaust gases can flow through the turbocharger much quickly – increasing the power generated for the turbocharger. With this, the turbocharger can work harder, suck more air and deliver it to the combustion chamber. 

Downpipe comes in two types: catted downpipe or catless. CAT refers to catalytic converter – a device used to convert the toxic exhaust gases into non toxic ones before they are allowed to leave the car. Catted downpipe includes a catalytic converter, whereas catless catalytic converter does not. 

Aftermarket downpipe can give a significant boost in horsepower if tuned – 50 to 75 horsepower is possible. If left unturned, you can expect to gain additional 25 horsepower instead.

Now the recap is done, let’s focus on the sound! Sorry if that took too long. It’s crucial that you understand turbo and downpipe before we discuss the sound change. 🙂

Catted downpipe with catalytic converter

Why Does Aftermarket Downpipe Make Car Louder? 

In general, sound becomes louder if they are traveling through hollow spaces. Do you notice that you sound louder when speaking in an empty unfurnished house? Or when you strike with an empty water bottle they make more sound when compared to striking with a full water bottle. 

This happens because sound waves collide with surfaces, get reversed into each other and cancel out. The more collisions they have, the more they cancel out – causing them to be less louder. Note that sound waves can also collide with air particles in the surrounding. 

I mentioned that aftermarket downpipes are wider when compared to stock downpipes. This makes it easier for sound waves to travel without colliding into surfaces and cancel out.

Aftermarket downpipes also reduce exhaust pressure. This is because they equip catalytic converters that are less restrictive. Look at the inside of the catalytic converter below. One is restrictive and another is less restrictive. 

stock restricted catalytic converter
Stock catalytic converter is very restrictive with fine holes
aftermarket high flowing catalytic converter
Catalytic converted in catted downpipe is high flowing (with bigger holes)

How Loud Will The Exhaust Be With Aftermarket Downpipe? 

Aftermarket downpipe can improve sound significantly. They make the exhaust sounds louder and more aggressive with deeper tones. I suggest you look for YouTube videos comparing the before and after sound for your specific car model and downpipe. If you can’t find them, at least research on forums.

Here’s a YouTube video showing you the before and after sound for an aftermarket downpipe.

Which Is Louder: Catless Downpipe Or Catted Downpipe?

Catless downpipes are always louder because they provide more space and lesser exhaust pressure for sound waves to travel. I wouldn’t say it’s significantly louder, but the difference is noticeable.

In exchange for the louder sound, catless downpipe will give off an undesirable smell – likely the unburnt fuel that’s not trapped by the catalytic converter. The smell is more apparent when you are stopped and you exit the car to do things like loading stuff off the trunk. 

You should not be able to smell it when you are driving. Though, some people have mentioned that they can smell it when they are idling at traffic.

My personal suggestion is to go with the catted downpipe. It smells horrible, you risk carbon monoxide poisoning and you will definitely fail your emissions test. All for a slightly bumped up sound and performance.

Will Aftermarket Downpipe Void Warranty?

No it will not. At the least, it should not. That’s because you are protected by the Magnuson-Moss Warranty act. In simpler terms, it states that a dealer (or any seller) can only void your warranty if they can prove that the damage is directly caused by your aftermarket install.

This means just because you installed an aftermarket downpipe, doesn’t mean your car warranty is void. Unless of course you damage something during your installation, then the warranty for that broken thing will be voided. 

I covered Magnusson-Moss Warranty act in more detailed in this article. It’s about muffler delete. Maybe you are interested 🙂 Does Muffler Delete Void Warranty?

Is Aftermarket Downpipe Legal?

No, aftermarket downpipes are not legal – especially the catless ones. They are sold for off-roading and racing purposes only. 

This of course depends on your local regulations. If you are driving in a strict state like California, then this is illegal for sure. Otherwise, you may have a chance to equip a downpipe and drive on the street without getting into trouble. 

California regulation states that a car can sound as loud as 95 dBA. Your aftermarket downpipe will not go as loud as this – regardless catted or catless. So no issue here. 

The worry is the emission test. Catless downpipe will fail you because they remove the catalytic converter – the one responsible to reduce emission. Catted downpipe, however, still equips a catalytic converter – although it will be an aftermarket one that’s less effective for emissions.

I suggest you research on forums or check with the shop. Different states have different laws, I can’t outline all of them here.

Will Aftermarket Downpipe Turn Check-Engine-Light On?

Catless downpipe will definitely turn your Check Engine Light (CEL) on. Whereas catted downpipe may or may not – it depends on the configurations for each car. But I would say yes, it would. 

The reason is because your car’s computer still thinks that you have the stock catalytic converter on but the exhaust gases flowing are still highly toxic. The car’s computer thinks the car is not operating efficiently and will turn CEL on.

You could turn the CEL off by re-configuring your car’s computer (tuning). Or install spacers on your exhaust pipe, so the O2 sensor is not placed directly into the exhaust gases. Rather some distance away, where the toxic gases are not so concentrated.

See below diagram to see what I mean by spacers. 

Oxygen sensor mounted on exhaust
Spacers will add distance between O2 sensor and the exhaust. The O2 sensor will not be inserted so deeply and it won’t be reading directly from the exhaust flow.

Should You Install Aftermarket Downpipe?

This depends on what you want. If you are looking for an improved horsepower, then yes, go for it. Aftermarket downpipe is a good way to increase horsepower for turbo cars. 

Make sure you bring your car for a tune afterwards – so your car can fully leverage the mod. Expect to get additional 50 horsepower or more if you install an aftermarket downpipe and then tune it. 

Just make sure you install a catted downpipe instead of a catless. I think the catted downpipe is good enough for performance and will save you headaches from the failed emission test and the unpleasant smell. This is especially true if you are installing it on your daily. 

If you want to install downpipe just for the sound, then no. There are many better and cheaper ways to improve car sound. See the alternatives below for improved sound.

Alternatives For Improved Sound

Cold Air Intake

Cold air intakes are marketed to boost horsepower, but I think the real gem is the sound improvement. The sound of air rushing into the car when you accelerate is just awesome. Here’s a YouTube video in case you don’t know what I am talking about. Skip to 3:59

If you want to know more about cold air intake and its impact on sound, I have an article for that over here.

Resonator Exhaust Tip

Resonator exhaust tip is the cheapest car mod you can buy for a more aggressive exhaust sound. Although cheap, they are surprisingly good. You will notice the sound change immediately. 

Here’s a YouTube video to show the before and after of resonator exhaust tip. They are cheap and easy to install – just clip on your existing exhaust tail.  

Performance Muffler

Performance muffler allows you to choose exactly how you want your car to sound. Do you want it extra loud? Very aggressive? Or with deep tones. I am sure you can find the aftermarket muffler for those. 

For an aftermarket muffler I suggest you get one that’s aggressive and louder but not so loud that it causes deaf ears for you and the people outside. If you agree with me and you are looking for a performance muffler, then I suggest you look at the Flowmaster Super 40. 

I have an article here where I discuss what you should look for when choosing a performance muffler and why the Super 40 is my go to. Check it out if you are interested. 🙂

Flowmaster super 40
Flowmaster Super 40
Ifandi L.

Ifandi L.

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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