Catalytic Converter Delete 101: Horsepower, Sound & Cost

So, you are interested in more horsepower and you heard removing the catalytic converter can do just that.

Sounds interesting! But there are still so many questions – does it really work? How much horsepower can you gain? Will you damage any engine? 

The same thoughts were in my head – so I understand where you are coming from. Thus, I am writing this article. 

The quick answer is Yes. Removing the catalytic converter can improve horsepower and will make your car go faster and provide improved sound – especially if you are running a big V8 engine. 

However, there are implications for removing the catalytic converter – mostly legal issues because this type of mod isn’t allowed by the state and can get quite loud – especially when cold starting.

Why Removing Catalytic Converter Can Increase Horsepower

Removing the catalytic converter can increase horsepower because it reduces backpressure – allowing your car to expel more exhaust gases and providing more room for air to enter the combustion chamber and create bigger combustion.

Catalytic converter (CAT) is responsible for breaking down toxic components in exhaust gases as they pass through. They work really well – which is why we don’t have as much smog anymore as we did in the 60s or 70s.

Unfortunately the cat is made of honeycomb structure that can be extremely restrictive. It takes some effort for exhaust gases to flow through them.

Thus, causing exhaust gases to flow slowly and unnecessarily occupying the combustion chamber.

By removing the CAT, you allow the exhaust gases to leave quickly. Which means the combustion chamber is now vacant and more air can enter to create big combustion. 

At best, you can gain additional 15 horsepower when removing the CAT. This depends on the engine size – bigger engines have the potential to gain more horsepower when backpressure is decreased. 

If you bring your car to a tune after removing CAT, you can even double the horsepower gain to 30 horsepower. Let’s talk a little more about tuning next and whether you need it or not for this mod.

Catalytic converter delete

Exhaust pipe where CAT has been deleted is less restrictive and reduce backpressure.

Do You Need To Tune After Removing CAT?

Tuning is required after removing catalytic converter to ensure the car’s computer (ECU) is calibrated and provide you with the most performance. 

Removing CAT can significantly reduce backpressure and tweak your air/fuel ratio. Without tuning to calibrate the ECU, you will likely face these issues:

  1. Check Engine Light (CEL) is on. With the CAT gone, your car’s ECU is going to assume your CAT is broken because the amount of toxic gases present in the exhaust gases are high. Tuning is required to turn this off.
  2. Incorrect air/fuel ratio. With the CAT gone, your car will significantly lose backpressure. This is good for performance but you must tune it! Otherwise you risk running lean when there’s too much air in the air/fuel mixture.

Removing CAT without tuning is a horrible idea. Your engine will not run well – don’t skip it. 

Also, aside from fixing air/fuel ratio, there are many things you can tweak by tuning. For example,  things like removing rev limiter, or tweaking engine torque map are common and could further improve the performance of your car.

More info on this article: How Much HP Can You Gain From Dyno Tune?

Is Catalytic Converter Delete Legal?

Running a car without catalytic converters is not legal – the actual law depends on the country or state you live in.

Some states are not that strict, while other places like California will fine for the over-modifying and pollution.

The most important thing about removing CAT is failing your smog test. You will not be able to register your car in areas where smog tests are done regularly.

The only solution is to bring the car back to factory specs and pass the inspection.

Make sure you research the laws in your area thoroughly before you perform this mod.

Will Catalytic Converter Delete Damage Engine?

Removing the Catalytic converter will not damage your vehicle as long as you tune it afterward. On the contrary, it can make your engine feel alive by removing the backpressure that is created between the catalytic converter and the exhaust manifolds. 

The benefit of removing the catalytic converters for your car is clearly power, without catalytic converters you could gain 30+ horsepower (with tune). 

There are even cases where 50 horsepower is gained. This can apply to engines that are extremely restrictive like diesel cars.

Diesel cars are not that popular in the USA but the diesel truck is extremely popular, many pickup truck drivers are removing their catalytic converters and running coal. 

This causes huge pollution, and it is not recommended – you can also get a decent fine from this. So avoid it! This is just for your info.

6 Reasons Why You Shouldn’t Perform CAT Delete

The benefits of removing catalytic converter are clear – you significantly reduce backpressure and gain horsepower. However, the downsides are also huge. 

CAT delete should only be done for race cars that are operating on track. Performing this on a regular street car is not recommended.

Here are 6 reasons why you shouldn’t perform CAT delete – especially for a regular street car.

  1. CAT delete is Illegal. After performing CAT delete, you will definitely fail smog inspection. This means driving your car becomes illegal and the fine could be huge depending on where you live. 
  2. Horrible pollution. Without a CAT, your car’s exhaust becomes extremely toxic – full of Carbon Monoxide and HydroCarbon. Driving your car will greatly pollute the environment. 
  3. Bad for health. Some of the toxic exhaust from CAT delete may seep inside. Breathing it in continuously can damage your health. Carbon monoxide poisoning is very common and should not be taken lightly. 
  4. Lose warranty. After removing your CAT, the warranty on the CAT, mufflers and exhaust system are void. I strongly recommend not going for a CAT delete if your car is relatively new. 
  5. Needs tuning that can be expensive. Tuning after a CAT delete is mandatory. Depending on what tuning you do, the price may reach up to thousands. You should consider this before deciding on a CAT delete.
  6. Reduced resale price. If you ever plan on selling your car again, performing a CAT delete will significantly reduce it’s resale price. Especially if the buyer is a non-car guy.
Image of exhaust with black smoke

Black smoke may happen with CAT delete.

How Much Does CAT Delete Cost?

CAT delete doesn’t cost a lot, it can be done for less than $50 when done by yourself or can cost about $300 (not including tune) if done by a workshop. 

If you have access to a grinder, I recommend you watch a YouTube video and do it yourself. It’s not that hard and could take an hour or two – depending on your experience.

Here are the steps to performing a CAT delete:

  1. Purchase a pipe extension with the same diameter as your current exhaust pipe. This is required to replace the CAT. Pay attention to the inner and outer diameter of the pipe when purchasing. 
  2. Jack your car up on an even surface.
  3. Locate the CAT and remove the clamp that’s holding the CAT on to your exhaust. This is usually done by unscrewing the bolts.
  4. Replace the CAT with the pipe extension that you purchased. You may need some welding depending on the setup you have.
  5. Keep the CAT in storage in case you want to reverse the CAT delete in the future. Don’t throw them away because CATs are super expensive. 

You can get the pipe extension from Amazon.

Here’s a great YouTube video from Donut media. They discussed CAT delete in general and also showed you how it’s done. 


Cutting your catalytic converter is going to give you a bunch of horsepower – that is true but you should never do it on a daily street car.

Mostly because it is illegal – you are not going to pass the inspection and it’s horrible for the environment!

What ends up happening is you being forced to put back your CAT and costing additional money (or time) in the process.

If you are serious about making horsepower, you should save up some money and go the proven route of installing turbo or exhausts. 

Here’s an article I have which you might find interesting:  5 Ways To Increase Horsepower That Works (And 5 That Doesn’t)

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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