Up-pipe Vs Down-pipe (And Why Modify Them)

By September 23, 2020October 5th, 2020Common Questions, Downpipe

Up-pipes and down-pipes – what do they do? How are they different? I only have a budget for one – which one should I install? You will get the answers to all these after you are done with this article 🙂

In the meantime, here’s a quick answer. Up-pipe is a piping that connects the exhaust manifold with the turbo. Exhaust gases enter the turbo from the up-pipe. Down-pipe is a piping that connects the turbo with the rest of the exhaust pipe. Exhaust gases leave the turbo from the down-pipe. 

Now let’s jump into the details.

Recap: What’s Turbocharger?

Up-pipes and down-pipes are parts required to install a turbo. So before we can talk about them, we must first understand what’s turbo and how it works. By the way, turbo and turbocharger mean the same but I will call it as ‘turbo’ for now because it’s shorter 🙂

Turbo is a car part that can significantly boost horsepower – additional 100 horsepower is achievable (this is a lot). You see – a car generates power by creating combustion in the combustion chamber. 

Combustion is an explosion that requires both fuel and air. To improve horsepower, you need bigger combustions – which means more air and fuel in the combustion chamber. Getting extra fuel is easy – your car can just inject more.

Getting more air is the tricky part. Turbo is an air compressor that’s self-powered by rotating a turbine. Remember I said combustion generates power for the car? Combustion also generates toxic exhaust gases as byproducts.

As these toxic exhaust gases flow out from the combustion chamber, they spin the turbine and power the turbo. As an air compressor, the turbo will then suck surrounding air from the environment, compress them and feed them into the combustion chamber. 

With this additional air, your car can then generate bigger combustions and provide that extra horsepower. That’s basically it – quite simple 🙂 If you want to know more about turbo, I have an article covering tubos in depth. Give it a read. Which is better: turbocharger or supercharger? 

Image of turbocharger
1
Exhaust gases enter turbo and spin turbo
2
Turbo sucks air from surrounding and compresses
3
Turbo delivers compressed air into combustion chamber

Recap: What’s Up-Pipe And Down-Pipe?

Earlier I said exhaust gases leave the combustion chamber and flow through the turbo to spin its turbine and power it. What I did not mention was – how exactly does exhaust gases flow from the combustion chamber to the turbo?

 

This is how it goes:

  1. Exhaust gases generated in combustion chamber
  2. Exhaust gases exit combustion chamber through the exhaust manifold
  3. Exhaust gases flow through up-pipe and reach the turbo
  4. Exhaust gases exit turbo and flow through down-pipe
  5. Exhaust gases reach the exhaust pipe and eventually exit the car

 

Did you catch what the up-pipe and down-pipe does? If you don’t, up-pipe allows exhaust gases to flow from the exhaust manifold into the turbo. And then down-pipe allows exhaust gases to exit the turbo and enter the exhaust pipe.

uppipe downpipe on turbo
Up-pipe allows exhaust gas to enter turbo from exhaust manifold. Not all cars have up-pipe. If there’s, it will be located here.
Down-pipe allows exhaust gas to leave turbo to exhaust pipe

Aside from allowing exhaust gases to flow, up-pipe and down-pipe also come equipped with catalytic converters (CAT). CAT is responsible for converting the toxic exhaust gases into non-toxic ones. I cover CAT in more detail in this article. What happens when you don’t fix a catalytic converter?

In short, up-pipes and down-pipes allow exhaust gases to enter and exit the turbo. They also equip CAT – which convert the toxic particles in the exhaust gases into non-toxic ones.

uppipe
Up-pipe
downpipe
Down-pipe

Why Modify Up-Pipe And Down-Pipe?

Stock up-pipes and down-pipes are not designed with performance in mind. They are narrow and can be quite restrictive. This means exhaust gases can’t flow through it easily and as a result, they won’t generate that much power for the turbo to work.

Aftermarket versions fix this issue by making the pipes as high flowing as possible. This means wide piping that does not have so much bending – allowing exhaust gases to flow quickly so they can spin the turbine that much harder. 

In addition to wide piping, aftermarket versions also come with catalytic converters (CAT) that are high flowing (catted pipes). Or they can even remove the CAT altogether (catless pipes). Refer to the picture below on what I mean by high flowing CAT.

stock restricted catalytic converter
Restrictive catalytic converter. Holes are very small
aftermarket high flowing catalytic converter
High flowing catalytic converter with bigger holes

All in all, aftermarket up-pipes and down-pipes ensure the exhaust gases can flow freely. Allowing them to generate more power for the turbo – so the turbo can suck even more air and feed them into the combustion chamber for more horsepower. 

Which One To Modify?

This depends on what you want. If you want a more responsive and aggressive feel, then go for the up-pipe first. Up-pipe is the entry point to a turbo. – it will give you a boost in horsepower at the lower RPM range – starting from 2000 – 3000. This will make your car feel more aggressive and responsive. Without a tune, I expect an up-pipe to provide around 10-15 horsepower. 

That being said, down-pipe should be able to provide slightly more horsepower. Without a tune, I expect a down-pipe to provide additional 20-25 horsepower. If you just want the overall horsepower, then go for the down-pipe first. But I personally would go for the up-pipe first, given the reasons above. 

Do note that even if you are just replacing one, you need to take off both the stock up-pipe and down-pipe. This is why many people would go ahead and purchase both aftermarket up-pipe and down-pipe since they will be doing the work anyway.

If that’s also what you want to do, then you should go expensive on the up-pipe but cheaper on the down-pipe. As I said, up-pipe will make your car more responsive because of the improvement in lower RPM range. 

No matter what brand you buy, always opt for the catted versions. Catless versions remove the catalytic converter for even more power gain. But I say this is not worth it because of these points:

  1. Catless versions would give off an unpleasant smell when your car is at idle.
  2. It’s extremely bad for the environment 
  3. Your check engine light will definitely turn on 

Will They Improve Exhaust Sound?

Yes! Aside from the horsepower gain, up-pipe and down-pipe will improve the exhaust sound – making it more aggressive with a deeper tone. 

Your car won’t become super loud but the sound change is noticeable and satisfying. This is actually perfect, because cars that go too loud are just horrible. With aftermarket up-pipe or down-pipe, that won’t be the case. 

If you want to know the specifics, the exhaust sounds louder because with wider diameter, sound waves can travel more efficiently – without clashing into one another and cancel out. I cover this topic in more detail in this article. Does downpipe make a car louder?

Do They Need A Tune?

If you want that performance, then for sure yes! A tune can significantly increase the horsepower gain. With a tune, I expect an up-pipe to provide 30 horsepower and downpipe to provide 50 horsepower. 

Tuning allows your car to fully take advantage of the aftermarket pipes. It could also configure the computer so that the check engine light is not turned on. I recommend you tune your car after installing aftermarket up-pipe or down-pipe.

Are They Legal?

Sadly aftermarket up-pipes and down-pipes are not legal. They are sold to be used on race tracks and off road. 

If you are driving in a strict state like California, then aftermarket up-pipes or down-pipes are definitely illegal. Otherwise, there might still be a chance. I suggest you chat with the store which sells you the aftermarket pipes. If they don’t know, reputable brands should have this information listed on their websites.

Which muffler is your car right now?

I would say that if you are driving in a state that’s not so strict, aftermarket up-pipe or down-pipe should be fine. Just make sure you get the catted version.

Should You Install Them?

If your car has a turbo and you want to increase the horsepower by a good amount then yes, go for it. Just make sure you get a catted version and bring your car to tune afterwards. I am sure you will be pleased with the performance gain – or at least the sound improvement 🙂

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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