What Happens If You Drill Holes On Your Catalytic Converter?

By August 9, 2020May 31st, 2021Common Questions, Maintenance

Are you looking to drill holes on your catalytic converter to increase performance? Or you are looking to unclog it? Either way – listen up folks.

Drilling holes on a catalytic converter is never a good idea. By doing so – you allow toxic gases to leak out. At best, this will pollute the environment. At worst, these toxic gases could enter your car and poison you. The toxic gases are odorless and colorless – so you wouldn’t even notice them. Not to mention – if your states require regular emission tests, then you will definitely fail them. So don’t do it. There are many better ways to unclog a CAT or to improve performance. 

Now that’s out of the way – let’s go into the details.

Function Of Catalytic Converter

I am assuming you know that your car generates toxic exhaust gases… Right? If you don’t,  long story short – a car needs to create combustion to generate power. This combustion will generate toxic gases like Carbon Monoxide and Nitrogen Oxide – which flow out of the car through the exhaust system. 

But wait! Releasing toxic gases into the environment – isn’t that horrible pollution? Absolutely. That’s why we have the catalytic converter (CAT) – to convert these toxic gases into less harmful ones. For instance, Carbon Monoxide is converted into Carbon Dioxide and Nitrogen Oxide is converted into Nitrogen and Oxygen. A CAT is positioned in the exhaust system – so these toxic gases pass through it and become non-toxic when they exit the car. So far so good – we now know why a catalytic converter is needed. But why do people want to drill holes in them? Let’s  cover that now.

illustration of a car exhaust system
Catalytic Converter in exhaust system.

Why Drill Holes On Catalytic Converter?

Increased Performance

You see – the holy grail of increasing car performance is to have as much oxygen as possible in the combustion chamber. More oxygen allows your car to create bigger combustion. Thus, delivering more performance and horsepower. Cold air intake, turbos, nitros and almost every other performance upgrade works by delivering more oxygen into the combustion chamber. 

A Catalytic Converter on the other hand, restricts oxygen from entering the combustion chamber (well, kinda). Picture this – Oxygen enters the combustion chamber, where they are used up to create combustion. In return, combustion creates exhaust gases that need to leave the combustion chamber as quickly as possible. I say ASAP because the longer the exhaust gases stay in the chamber, the more space it occupies – preventing fresh oxygen from entering for the next combustion. 

With a Catalytic Converter on the way, these toxic gases cannot flow directly out of the car. Instead, it has to go through the catalytic converters that only have small-honeycomb openings. These kinds of restrictions in the exhaust system is known as backpressure. They prevent fresh Oxygen from entering the combustion chamber because exhaust gases cannot move out quickly. Thus, decreasing the car performance. 

Drilling holes in the Catalytic Converter could reduce this backpressure – allowing the exhaust gases to escape prematurely. Thus, providing more space for Oxygen to enter the combustion chamber for a more powerful combustion.

Horrible For The Environment

Many countries have implemented strict emission regulations for a long time – and yet, the pollution is still horrible. If cars with CAT  are already causing this much harm, how much more do you think cars without CAT will cause? The cat exists in the car for a reason – don’t try to damage them. 🙂

Image of exhaust with black smoke
Toxic Exhaust Gases

Carbon Monoxide Poisoning

If you don’t care about the above points, then what about this? Drilling holes in your CAT could be dangerous even for you! The toxic gases that exit from the holes on the CAT could seep into your driving space – causing your Carbon Monoxide poisoning. 

This is especially dangerous because Carbon Monoxide is odorless and colorless. You wouldn’t know you are inhaling them until you have the side effects – including dizziness, vomiting, blurred vision and Loss of consciousness. These are short term side effects. Prolonged even further and you could have permanent damages in the heart and brain.

Again, I suggest you not do this and look into other methods to achieve your goals. Typically, they would be to clean a clogged CAT or to increase performance. Now let’s talk about both of them 🙂 

How Do I Clean A Catalytic Converter?

Clean With Laundry Detergent 

This is the easiest method. Take off your catalytic converter and soak it in  laundry detergent water overnight. The insides of a catalytic converter is made up of thin honeycomb structures that could get clogged easily. Soaking the catalytic converter overnight on soapy water like laundry detergent can help to remove the dirt.

Image of Catalytic Converter on Detergent Water
Soak CAT in Laundry Water

Don’t Clean With Lacquer Thinner 

You may find suggestions to fill a gallon of lacquer thinner on your half empty gas tank. This will supposedly clean out your catalytic converter as you drive. I personally do not recommend this method. We do not know exactly what’s included in the lacquer thinner. For you to be putting such a solution into your gas tank is absolutely not worth it.

Image of Lacquer Thinner
Image of Lacquer Thinner

Cheap Ways To Increase Performance

If what you really wanted was to increase performance and drilling holes on CAT was something you considered – then I am guessing you are a little tight on budget. The list of performance mods below are relatively cheap and easy to do.

Cold Air Intake

Cold Air Intake is always the first performance part that I recommend enthusiasts to install. A CAI aims to increase performance by sucking in cold air for combustion. Cold air is more dense and thus, contains more oxygen. 

A good cold air intake can cost about $200 and brings lots of benefits:

  • Slight increased in horsepower
  • Improve the sound of your engine greatly
  • Looks cool as hell once you open up the hood

I cover cold air intake in depth in this article.

Cold Air Intake Image
Cold Air Intake

Muffler Delete

Muffler delete means removing the muffler from your exhaust system. This is similar to removing or drilling holes on your CAT. The idea is to allow exhaust gases to flow freely in the exhaust system – so they can leave faster and provide more space for Oxygen in the combustion chamber.

When compared to removing or drilling holes on a CAT, muffler delete is a much safer option. Although it decreases backpressure and could increase car performance, the sound of your car engine will be extremely loud and downright deafening at times. Not to mention, it’s illegal in some states to remove the muffler. Proceed with caution.

Image of straight pipe exhaust
Exhaust pipe without muffler


Tuning means reprogramming the car’s computer and changing the way your car performs in different situations. Tuning a stock car will not provide you with extra horsepower. However,  you can make your car feel more performant and aggressive by tuning values like these:

  • Removing rev limiter 
  • Removing top speed
  • Changing the air/fuel ratio 
  • Tuning the values in Engine Torque Map 

If you are interested to know more, I cover dynotuning in this article

Car Tuning
Tuning Car’s Computer
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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