CAT Delete or Gutting: Pros, Cons, Performance and Cost

Taking off the catalytic converters, also called CAT deletion, gives more horsepower but also brings along some issues. On positive side, CAT delete reduces backpressure, letting the engine breathe better and make more power – expect to see 10 to 15 extra horses, especially with strong V8 motors. However, the catalytic converters are there for a reason – they reduce pollution from the exhaust. Removing them means more nitrogen oxides and particulate matter (soot) coming straight out the tailpipes. This extra pollution is why CAT deletion is illegal many places due to violating emissions laws. By deleting CAT converter, some drivers want the louder sound, but it can be a nuisance in neighborhoods. Do your homework on local laws, as getting caught can bring steep fines.

CAT delete

Here is what the user said after a secondary CAT delete:

“Removing the secondary cats def makes a big difference. My car dyno’d at 407rwhp on a mustang dyno which is a 26% drive train loss. So that puts my crank HP at around 550. That’s a 50hp gain with just a cat back exhaust(no secondary cats).”

Some Key Insights for You
  • Deleting the catalytic converter increases horsepower by reducing backpressure, but it is illegal in some areas.
  • Removing the catalytic converter takes away its ability to clean toxic emissions, increasing pollution.
  • Deleting the cat gives a louder, deeper exhaust tone that some people find annoying.
  • Catalytic converter removal can void the engine warranty if removed.
  • Replacing the cat with a straight pipe is better than using a gutted converter.
  • The cost is around $70-200 for a DIY install or $350-650 to have a shop do it.
  • Check your local laws before modifying the exhaust system. There can be steep penalties for violations.

Why Is A Catalytic Converter Important?

A catalytic converter is a device in exhaust systems that breaks down harmful emissions (CO, NOx and HC) into harmless substances (H2O, N2 and CO2). The reason why it is important is that it helps protect the engine from damage due to excessive emissions. 

Catalytic converters work by using precious metals called catalysts, which contain platinum, palladium and rhodium coated on a ceramic honeycomb substrate. These metals are used to convert toxic substances into less harmful ones. 

catalytic converter schematic

The metal casing of a catalytic converter is another important component surrounding the core of a catalytic converter. This metal casing directs the exhaust gas flow through the catalyst bed. The metal casing is usually made out of stainless steel.

In engines, three-way catalytic converters are used that have the benefit of performing the oxidation of carbon monoxide (CO), hydrocarbons (HC) and the reduction of nitrogen oxides (NOx) simultaneously. They are operated at elevated temperatures greater than 600°C.

Legal Requirements of A Catalytic Converter

In some countries, catalytic converters are required to meet certain standards. They are also mandated by law in many states and localities.

Driving a vehicle without a catalytic converter will fail an emission test, making it illegal to drive. It could also cost you a heavy penalty.

“According to Alabama’s pollution laws, driving a car in the state is illegal if its catalytic converter has been removed, switched or is not functioning correctly. Anyone who violates the law faces a $10,000 fine and a year in jail.”

Environmental Protection Agency (EPA) issued the following requirements for the legal removal of catalytic converter and installation of aftermarket catalytic converters:

  • The vehicle manufacturer’s warranty for the stock catalytic converter has expired. Warranties are a minimum of 8 years/80,000.
  • An inspection of the vehicle has determined that the existing converter needs replacement.
  • It should be installed in the same place as the stock CAT converter.
  • Aftermarket catalytic converter should be CARB (California Air Resources Board) certified.
  • CARB-certified catalytic converters are mandatory for 1993, 1994, or 1996 and newer vehicles. For 1992 or older vehicle models, EPA-certified aftermarket catalytic converters can be installed.
  • The aftermarket catalytic converter should be of the same type as the stock catalytic converter (two-way, three-way).

Is Catalytic Converter Delete Legal?

Whether removing your catalytic converter is illegal or not depends on where you live. Some places have stricter emissions laws than others.

For example, in California, it’s against the law to drive without the proper emission control devices installed. Vehicles in California must meet emissions standards. Driving without a cat converter leads to fines.

The rules vary by location. What’s allowed in one state may not fly in another. Before modifying your ride, be sure to check your local and state laws. Make sure your vehicle can legally (and safely) cruise your streets.

CAT Delete Pros

There are some great benefits of deleting catalytic convertors that excite vehicle owners. Let’s discuss what they are:

1. Increasing Horsepower

Deleting catalytic converters removes restrictions in the path of exhaust gases. It significantly reduces the frictional losses and back pressure, allowing exhaust gases to flow freely.

As a result, the engine piston does not have to work hard to overcome the friction and remove exhaust gases from the engine cylinder during the exhaust stroke.

When exhaust gases could easily be removed during the exhaust stroke, the engine cylinder will be easily replenished with more fresh air for the next combustion cycle. As a result, it will increase engine efficiency and increase engine horsepower by up to 10%.

You can read my guide on straight pipe exhaust systems to understand the concept of back pressure.

Back pressure is a myth and some people think higher back pressure means the engine will have better performance. But that’s not correct. So, please read the full guide I have linked above as I have explained with facts. This will help you understand what I’ve explained below.

You can also read my guide on whether straight piping after CAT delete affects MPG or not.

2. Weight Reduction

Catalytic converter contains some heavy components, so deleting it can potentially lighten your ride.

Inside the stainless steel shell lies a ceramic honeycomb structure coated with precious metals like platinum, rhodium and palladium. Add it all up and a cat converter can tip the scales at 4 to 8 kg.

Less weight = quicker acceleration. So by ditching the converter, you reduce the overall mass of your vehicle. This lets your engine put more pep in its step when you step on the gas pedal.

3. Lesser Overheating Of Your Engine

CAT delete also results in overheating of the engine. Since the engine has to do less work to push exhaust gases through a catalytic converter, the engine will remain cooler. Moreover, if a catalytic converter is clogged with carbon and ash deposits, it will block the natural flow of exhaust gases, which will cause the exhaust manifold to heat up

4. Smooth Throttle

By deleting the catalytic converter, you will experience a smooth throttle when you push a gas pedal. 

When the car starts moving, the catalytic converter gets heated up by the exhaust gases that go through it. Once the engine is warmed up, the catalytic converter starts working efficiently.

However, when a catalytic converter’s honeycomb substrate is clogged, it will severely restrict your engine’s ability to exhale. If the engine can’t exhale, it will not be able to inhale fresh air. An engine that can’t breathe well will stall and you will not experience a smooth throttle.

5. Amazing Deep Exhaust Sound

In V8 engines, deleting the catalytic converter results in an amazing deep roaring sound of exhaust gases that car enthusiasts like to hear when they push the accelerator pedal.

However, for some vehicles, CAT Delete causes a crispy, rattling or popping sound which can irritate the people in the surroundings.

One user says this:

“I replaced the cat with a straight pipe on my old ’95 3.4L and did not like the rasp at all! Other than that, no negatives.”

CAT Delete Cons

Here are the cons of deleting catalytic converter:

Air Pollution

Catalytic converter reduces the amount of pollutants coming from the vehicle and makes the exhaust system cleaner, improving the quality of the air that comes out of the tailpipe.

After removing a catalytic converter, a vehicle will not be able to pass the emissions test. Your vehicle will emit more pollutants than before.

Toxic pollutants, such as carbon monoxide, nitrogen oxides, and unburned hydrocarbons will be released into the atmosphere from your vehicle, resulting in smog which will cause several lungs related issues.

However, if your vehicle has two catalytic converters, removing the secondary catalytic converters could still pass you the emission tests while freeing up some horsepower at higher RPMs.

Voiding Vehicle’s Warranty

Any modifications that you make in the engine, such as CAT Delete, can void its warranty. It means that if you face any problems in your engine after removing the catalytic converter, you will not be able to fix it for free.

Requires ECU Tuning

CAT Delete also requires ECU tuning. As you are messing with the exhaust system, the ECU detects changes, throws a warning code, and can turn on the check engine light. 

There are two oxygen sensors in the engine. One is before and another is after the catalytic converter. The first oxygen sensor measures oxygen in the exhaust gases so that the air/fuel mixture can be adjusted. The oxygen sensor after the catalytic converter measures its efficiency. 

After a CAT delete, the O2 sensor, which is downstream of the catalytic converter, will record high oxygen levels in exhaust gases, due to which the ECU (Engine Control Unit) will think that the catalytic system is not functioning efficiently. As a result, it will show the P0450 code, turn on the check engine light and also put your vehicle into reduced power mode.

You can install a small O2 sensor adapter into the exhaust system that will move the second O2 sensor out of the exhaust stream, due to which the ECU will think that the catalytic converter is still present and is cleaning the exhaust gases. 

Decreased Resale Price Of Vehicle

After CAT Delete and installation of aftermarket exhaust systems, the resale price of a vehicle is reduced. Customers do not trust the engine’s performance after CAT delete, and they also don’t want to get into trouble to buy vehicles that are not passing emission tests after CAT delete.

Gutted CAT vs CAT Delete (Straight Pipe)

Gutted CAT vs CAT Delete

If you’re confused about whether gutted (hollowed) CAT or CAT delete is better, I would recommend CAT Delete by replacing it with a straight pipe. The reason is simple i.e. lesser turbulence with a straight pipe compared to the hollowed catalytic converter.

A catalytic converter consists of a bunch of honeycomb-patterned catalyst bed that offers restrictions to the exhaust gases.

As you know that a catalytic converter has a larger size compared to the piping to which it is welded. If the catalytic converter is gutted, the absence of any restriction will dramatically reduce the flow velocity of exhaust gases. In engineering/physics, the larger the pipe diameter, the lesser will be flow velocity. Moreover, if exhaust gases flow from a smaller area to a larger area, their pressure increases in a region with a larger area which will try to push back the flow.

Due to the lack of restriction in a gutted catalytic converter, it will act as a pipe twice the size of straight piping.

For exhaust gases to flow easily, they should have higher velocity, which is only possible if some restriction is present or the diameter of the pipe is reduced. So, a flow of gases from a 2.5″ exhaust header to a 4″ hollowed catalytic converter will cause reversion and the exhaust flow will reduce dramatically.

Moreover, gutted CAT resonates more compared to the CAT Delete system. So, there is another drawback as resonation also impedes the gas flow.

Here is what a user said:

“I tried gutted stock cat. I tried a test pipe. I am running 2.5 gutted cat now. Test pipe performs better than a gutted cat.”

Catalytic Converter Delete Cost

The cost depends largely on whether you complete the delete yourself or have a professional mechanic do it.

Buying the piping and tools to cut out the catalytic converter and connect the new piping averages $70 to $200. With some basic mechanical skills, welding the new section is doable. However, lacking experience or proper equipment could lead to exhaust leaks or other issues.

Hiring an experienced mechanic to replace the converter with piping ensures proper installation. Expect to pay $350 to $650 for their work. While pricier, you gain peace of mind knowing the job was done correctly.

Some First Hand Experiences Shared By Users In Different Communities

Our team conducted research across various online communities, forums, and subreddits to gather user comments and opinions on “CAT Delete“.

User 1 says:

Did a CAT delete last month. Noticed a significant increase in exhaust sound, which I love. However, the fuel smell is a bit stronger now. Thinking about a tune to balance it out.

User 2 says:

Completed a CAT delete last week. The turbo seems to spool up quicker now. No error codes yet, but installed a tune just in case to optimize performance.

User 3 says:

Post-CAT delete, the car’s exhaust note is music to my ears. However, had to invest in a high-flow cat to keep things legal and reduce the environmental footprint.

User 4 says:

The CAT delete gave a nice bump in horsepower. But, I had to deal with the check engine light. A friend recommended a software reflash, and it worked like a charm.

User 5 says:

Did the CAT delete in my Audi S4 and loved the immediate difference in sound. But, I had to get a custom tune to avoid engine light issues. Worth it for the added growl and slight power increase.

CAT Delete: FAQs

Can I put a muffler where the catalytic converter was?

You can delete the catalytic converter and install a dual exhaust system, having a muffler. I would advise installing a true dual exhaust system in place of a catalytic converter as it allows the removal of exhaust gases from the combustion chamber at a faster rate. True duals are both exhaust pipes run by themselves and are not tied into one with a Y pipe.

Can I replace a catalytic converter with a straight pipe?

Yes, you can replace a catalytic converter with a straight pipe. It will increase the horsepower of your engine but your engine will not pass the emission test. Make sure that the diameter of the straight piping is not greater than the exhaust header pipe.

Do you have to have a catalyst converter in Utah?

You should have a catalytic converter in Utah.

What happens inside a car when a catalyst converter is empty?

If the catalytic converter is empty, your car will produce a loud rattling or crispy sound and dump much more emissions into the atmosphere.

Can a Mercedes run without the catalytic converter?

Yes, Mercedes can run without a catalytic converter but it will produce a deep roaring exhaust note in its V8 engine. however, Mercedes will start sending toxic gases into the environment after CAT delete.

Will removing my catalytic converter make truck exhaust loud?

Removing a catalytic converter reduces the restriction. So, your truck exhaust will be loud.

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