Removing Catalytic Converter – Is It Legal To Drive Without One?

There are plenty of guides online about removing your catalytic converter. But is it practical? Is it even legal?

As you might expect, there are several things that you need to know, including legal bits and bobs. Catalytic converters are vital emissions-controlling components within your car’s exhaust. When things go wrong, it can be pretty expensive.

In this article, I’ll explain what you can and can’t do when it comes to your exhaust system.

• What is a catalytic converter?
• Removing catalytic converter – legal?
• Removing catalytic converter process walkthrough.
• F-150 case study.
• Performance benefits without a cat.
• What is cat-back exhaust?

Related Content

• Catalytic Converter Replacement Cost And Why Cars Have Them
• How To Unblock A Catalytic Converter – And How To Diagnose

What Is A Catalytic Converter?

A catalytic converter is one of the most critical parts of your car’s emissions system.

It helps to reduce the number of harmful emissions by significant amounts. Specifically, it removes most of the NOx (nitrous oxides) and hydrocarbons (unburnt fuel) in the exhaust gases. The catalytic converter contains precious metals that act as a “catalyst” – something that causes or speeds up a reaction without being affected itself.

The harmful particulates in the exhaust react with the contents of the catalytic converter and produce carbon dioxide and water instead.

“Carbon dioxide?” — you might say. “Isn’t that the cause of most of our planet’s current problems? Global warming and all that?”

The answer is, of course, yes. Carbon dioxide-spewing vehicles are one of the main things that badly need altering if we are to preserve the planet as we know it for future generations (hence the introduction of electric vehicles). However, when it comes to internal combustion engines, carbon dioxide is the lesser evil. It’s harmful to the environment and the ozone, yes, but it’s not as immediately dangerous as NOx or hydrocarbons. Both of these could cause serious health issues.

A catalytic converter is, essentially, simply a network of honeycomb-looking passages within the exhaust. When the gases are forced through them, the cat removes many of the harmful chemicals.

How Does A Catalytic Converter Work?

As mentioned before, a catalytic converter works by using precious metals and honeycomb-like structures.

The precious metals within the cat speed up the natural reactions involving exhaust gases to ensure the majority of them happen before the gas expels itself out of the tailpipe.

Catalytic converters work to speed up the reactions that turn carbon monoxide, NOx (nitric oxide and nitrogen dioxide – together, NOx), and hydrocarbons into carbon dioxide, water, and nitrogen.

You can get two types of cat.

• Two-way catalytic converter – works with only two of CO, NOx, and CH.
• Three-way catalytic converter – reacts with all three.

By law, every new car must have at least a two-way cat.

What Chemical Reactions Are Involved?

All of the following formulas came from chemequations.com.

Carbon monoxide reacts with oxygen in the air to form CO2.

2 CO + O2 → 2 CO2

Likewise, hydrocarbons react with oxygen molecules, leaving water (H2O) and carbon dioxide.

4 CH + 5 O2 → 2 H2O + 4 CO2

When it comes to NOx, things are a little more complex. That’s because of the different types of NOx and the various ways in which they react. In short, they react and give out some combination of carbon dioxide, nitrogen, or water.

C + 2 NO2 → CO2 + 2 NO

2 CO + 2 NO → 2 CO2 + N2

4 CO + 2 NO2 → 4 CO2 + N2

2 H2 + 2 NO → 2 H2O + N2

Removing Catalytic Converter – Is It Legal?

Not if you’re not going to replace it, nope.

By law, cars MUST have a catalytic converter if they were fitted with one when they were made. You can’t remove it. It’s actually illegal, not just frowned upon.

Some would be of the opinion of, ‘If it’s just me, it can’t hurt.’ That might be true, but if everyone thought that way, we’d have a significant problem. For that reason, it’s illegal not to have a cat. End of story.

In that vein of thinking, there are aftermarket exhausts out there in the market with “fake cats”, also known as “dummy cats”. Despite the wide prevalence of them on the internet, they are, in turn, illegal. As you might begin to notice as you do more research, most of these dummy catalytic converters get made by custom exhaust producers. They aren’t usually sold as standard stock.

In states such as California with strict emissions laws, you’ll need a valid legal reason to replace the catalytic converter. You can’t just do it whenever you feel like it. The EPA (Environmental Protection Agency) released national guidelines regarding removing and replacing catalytic converters in 1986. You’ll have to abide by these laws.

So, what’s a valid legal reason for removing and replacing a catalytic converter?

Usually, it’s an emissions test. Your car will have to fail either a state or federal emissions test to “qualify” for a new one. This ensures the precious metals used within the component have the most extended lifespan possible.

In the next section, I’ll consider whether or not removing a catalytic converter yourself is possible and legal. It’s important to talk about because there are specific processes involved and things you need to know before starting.

Removing Catalytic Converter – Can I Do It Myself?

Within reason, it’s possible, but it also depends somewhat on what state you live in, as previously mentioned. To be frank, it would probably be best to leave this one to the professionals.

When you – or a mechanic – start the process of removing a catalytic converter, there must first be a valid reason. For that, you’ll need to have done an emissions test and failed it. All good.

During the removing process, you need to note down any imperfections you see with the cat. This situation is where it’s most beneficial to work with a mechanic. They’re more likely to know what the component should look like and, therefore, what’s visually wrong with it (if anything). Sometimes, there won’t be anything visually wrong at all. Still, usually, you’ll see either a carbon buildup or a broken honeycomb structure.

You have to document all the issues you find. For legal reasons, it’s best to find as many things wrong as you can. Take photos and save them, writing down descriptions of what’s happened. Under federal law, you can’t replace a fully functioning catalytic converter.

Once you’ve removed the old catalytic converter, you’ll have to install the new one. You can’t legally drive the car without a cat.

When you purchase a new one, it must conform to OEM standards – the original specifications that the manufacturers first made the part with. You can use an aftermarket cat provided it meets the OEM specifications.

There’s one exception to this rule, and that’s if you refit a “high-flow” aftermarket catalytic converter. Provided they’re certified by the EPA, you can install these on your car. The same rules still apply here, though – you can only remove and replace your catalytic converter if the original one was damaged or missing.

The replacement catalytic converter will come with a manufacturer warranty card. This card needs to be filled out along with the installation before being submitted to the appropriate place. The part’s warranty may specify the need for professional installation, in which case a DIY job would invalidate it.

With all this considered, you can see why – for legal reasons – it just makes more sense to leave the removing and replacement of a catalytic converter to a professional mechanic. Make sure to find a company you trust and one that, ideally, specializes in exhausts.

What Happens If I Drive Without A Catalytic Converter?

If you drive without a catalytic converter, it will – clearly – raise some serious environmental concerns. Instead of water and carbon dioxide, you’ll be churning out chemicals and particulates that are quite literally deadly to the human lungs.

Most importantly – and I can’t stress this enough – it’s illegal.

Most cars made after 1975 will come with a cat, and they must stay that way. If you drive something older than that, then, well, you’re free to do whatever you want.

Driving without a catalytic converter will also raise the following problems.

• Moral and ethical issues – you’ll be polluting the atmosphere badly and damaging people’s lungs as you go. It’s not worth it for a few extra horsepower. If you’re thinking more along the lines of track driving, then that’s an entirely different story.
• Check engine light will come on.
• Legal costs – it’s true; lots of people don’t get caught when removing their catalytic converter. Statistically, we’ve got no idea how many people get away with it – for obvious reasons. But we do know what happens when you get caught. You’ll have to pay a fine of £1,000 for a car or £2,500 for a van in the UK. In the US, you could be fined up the $10,000 for the act of removing it. When the police inevitably pull you over because of the excessive exhaust noise (or for any other reason), they’ll only suspend your smog certification (California). Is it removing your catalytic converter really worth it? I don’t think so.

How Much Would I Pay For A Replacement Catalytic Converter?

The cost of a new catalytic converter depends significantly on the vehicle – not to mention geography, the quality of the new part, labor rates, etc.

In a previous article, I’ve estimated (as a very rough estimate) the cost of a new catalytic converter to be somewhere between $800 and $1,200. For popular, common, everyday cars, it might be more like $400 to $600. Expensive vehicles – your supercars, big muscle cars, fancy brands, and such like – you can easily get into the many thousands of dollars in the blink of an eye.

Catalytic converters cost quite a lot because they contain a select amount of precious metals such as rhodium, palladium, and platinum. The part alone can easily be $600. The rest of your cost will be made up of labor rates and, potentially, insurance/warranties.

Example – Ford F-150 Replacement Catalytic Converter Cost

I thought it might be helpful to analyze the cost of a replacement catalytic converter on America’s most popular vehicle – the Ford F-150 truck. For this example, let’s assume a 2020 3.5 EcoBoost.

First, as mentioned before, our truck would have needed to fail an emissions test. You’re unlikely to have this kind of thing lying around at home, and so you’ll need to pop out to your local auto shop.

With a failed emissions test in hand, you can start looking for a new part. On OEMFord, we can filter the results to show only 2020 Ford F-150s (if you follow the link, I’ve done that for you). The 3.5-liter EcoBoost is turbocharged and, clearly, 3.5 liters, so we need to check for that information on the part.

The specific details are now up to you. Which exhaust does your truck have? Make sure to order the right one, as you may have to pay for shipping to return it if you accidentally get the wrong part.

OEMFord has four options available.

• $944 – single exhaust (right position).
• $836 – single exhaust (left position).
• $897 – dual exhaust (right).
• $671 – dual exhaust (left).

When you click checkout, you can enter your VIN to make sure the part fits. It’s always good to double-check.

If everything works out okay, you can go through with it and buy the part.

As you can see, prices for an average F-150 vary between $670 and $945.

Shipping costs will likely be somewhere between $50 and $100, so don’t forget to add that on too.

For parts alone on this job, you’ll therefore be looking at costs between $700 and $1,000.

For labor costs, at $100 per hour for between 1 and 2 hours (let’s say 1.5), you’ll be paying $150 again.

Finally, you’ll need to add taxes.

Overall, I’d estimate the cost of a replacement catalytic converter for a 3.5 EcoBoost 2020 Ford F-150 to be around $1,000 to $1,100.

It’s quite a lot, I know. But it’s probably better to pay that extra $150 for the labor and make sure everything is done properly and legally. It might save you hefty fines further down the road.

Ford F-150 – A Better Way?

There’s a better way of doing it, in my opinion.

That better way is: just leave it with the mechanic (as long as they’re a trusted company).

The mechanic and the shop can organize all of this stuff for you. And they’ll probably get it at a better price than you can because of trade discounts. Although customers often think they’re saving money by purchasing their own parts and then getting the garage to fit it for them, it actually usually ends up more expensive. Also, some shops (such as the one I worked at) refuse to fit customer-supplied parts for legal reasons.

If it’s imperative to you to get the best price possible, shop around a bit. Phone or email garages to get approximate quotes off them. Some may ask to see the car beforehand – this is absolutely fine, as they’re just gauging how much work needs doing and therefore what labor time they should charge. Just make sure they don’t start any work without permission!

Get these quotes in a broken-down format, so you can see what they’re charging for labor and parts. If you can get the catalytic converter for cheaper than they’re showing, try to haggle down to that amount. It’ll save you a lot of fuss and, in my opinion, is definitely the best way of going about replacing your cat. The technicians are there to do the work – let them.

What Performance Benefits Are There For Removing A Catalytic Converter (Illegally)?

As I’ve said many times, removing a catalytic converter can’t be done legally.

As a result, you can’t remove your cat and then drive on the road. However, if you were building a track-only car (meaning you would have to trailer it to the racecourse, too), then things are different.

Removing your catalytic converter would lead to many performance benefits. Most of these relate to the decreased load on the engine. These benefits include:

1. Increased horsepower – since exhaust gases can escape faster and there’s less back pressure, the engine will find a new lease of life. You might have to experiment with different types of exhaust to find the optimal one for your engine, as they’ll all have different specific designs.
2. Lower running temperature – since the engine has less to overcome, it can run cooler. You’ll find this tends to lend itself towards increased performance, as you can push the car further before it starts to overheat.
3. Better mileage – again, since the engine doesn’t have to work as hard, it becomes more efficient. As the engine works, it converts the chemically stored energy found in fuel into kinetic energy (moving the wheels). There’s much less to do without a catalytic converter in the way.
4. Greater exhaust sounds – okay, this isn’t a performance benefit. Still, everyone loves a good bit of raw engine noise coming out of an exhaust pipe. The catalytic converter acts as a muffler. Without it, you’ll hear a thunderous rumbling or roaring noise that’s quite something to listen to. Enjoy it where you can.

Again, all these can only apply if you drive the vehicle on a track that permits it. You might need to check the rules of the racecourse before you arrive just to make sure. Because the car doesn’t have a cat, you also won’t be allowed to drive it to the track on the roads.

Is A Cat-Back Exhaust Legal?

A cat-back exhaust is a portion of the exhaust pipe that runs from the “catalytic converter” to the tailpipe (the end of the exhaust) – hence, “cat-back”.

It includes the muffler(s), pipe(s) and tailpipe(s).

Getting a new aftermarket cat-back exhaust is perfectly legal, as it doesn’t affect the catalytic converter.

Usually, these exhausts have larger diameters, meaning more air can (technically) flow down them, increasing horsepower. They’re also often explicitly designed to make sure that the lower sounds are amplified. This is more for show than practicality.

Cat-back exhausts are very popular among the boy racer crowd, but they are generally more for show than anything else. You often see increased performance in the high rev ranges but decreased performance in the lower ranges. For practicality, especially for city driving, cat-back exhausts can actually lead to reduced power – ironically. They might be a good idea if you often drive quickly or spend a lot of time on the highway.

Removing Catalytic Converter – Conclusion

Let’s just emphasize this one more time.

Driving with a removed cat is illegal.

In fact, even removing the catalytic converter to replace it with a new one without a valid reason is illegal in some states.

Going against these laws could cost you some serious money.

The main thing to take away here is only to remove and replace your cat if it’s definitely broken. You can visually inspect it to some extent to see if you can see anything. Otherwise, it would be best if you tried some other techniques for cleaning out your engine and your exhaust system, such as Cataclean, OBD II scans, replacing oxygen sensors, or simply using premium gasoline.

Catalytic converters aren’t perfect. They aren’t a long-term solution but, for now, and the past 45 years, they’ve been reducing the damage cars do to the atmosphere and us. It’s worth leaving them where they are unless they’ve stopped working.

I hope this article on removing catalytic converters has been interesting for you and that you know what to do now. Feel free to leave a comment down below, and thank you for reading.