Catalytic Converter Delete Explained

The ever-popular cat delete is a simple but controversial upgrade. On one hand, it’s a great way to remove the most significant bottleneck in your exhaust, but on the other hand, it is illegal.

A lot of people go ahead with this upgrade anyway, especially if they take their car to the track often.

If you’re on the fence about whether or not you should remove your catalytic converter, and how you can go about doing it, then this article is for you.

This upgrade is something you want to thoroughly understand before going through with it.

There’s no doubt that deleting your catalytic converter has some performance advantages, but at the same time, there are some pretty serious drawbacks.

In this guide, we’ll tell you how to delete your catalytic converter — whether you should hollow it out (gut it) or remove it entirely, and the pros and cons of this modification.

What Is a Catalytic Converter Delete?

OEM catalytic converter installed

As the name suggests, a cat delete, or a catalytic converter delete, is when you completely remove the catalytic converter from your car and replace it with a straight pipe or a test pipe.

In order to remove the cat-con, you will have to replace it with something. When you do that, you need to choose the size of your replacement pipe carefully. You can either fabricate the test pipe or buy an aftermarket version.

Catalytic converter delete kit installed

To understand why cat deletes work, you need to first know exactly how the catalytic converter works. The general idea is to free up the most restrictive section of your exhaust.

Removing the cat-con does not have any detrimental effects on performance. If anything, it marginally increases power, depending on your tune and any other upgrades that you have installed.

Pros and Cons of Removing Your Catalytic Converter 

Before deciding whether a cat delete is right for your car, you need to know about both its advantages and disadvantages. The advantages of a catalytic converter have a lot to do with the performance gains.

The honeycomb structure inside your catalytic converter is coated with precious metals that help to filter out the harmful pollutants from your exhaust.

But because of the way it is designed, it creates a significant restriction in the exhaust flow path.

Cat-con honeycomb structure

It is this restriction that robs some of the engine’s power by creating exhaust back pressure. By removing the catalytic converter you’re removing this backpressure, and that’s what helps to improve engine performance. That is if it’s tuned correctly.

It’s one less component to worry about. Clogged or failing catalytic converters do more harm than good.

If you’re taking your car to the track frequently, getting rid of the cat-con will make things simpler, and in some cars, reduce overheating issues.

You can expect to see a gain of less than 5 hp by removing the catalytic converter. but this heavily depends on the car.

For instance, if it’s an old car from the 70s. Back then cat-cons flowed like bricks and seeing gains of up to 50hp from a cat delete wasn’t uncommon.

This reduction in backpressure (not to be confused with the scavenging effect) also leads to slightly improved fuel economy but it’s a marginal improvement.

However, while those are the pros, there are huge disadvantages. In all 50 states, it’s illegal to drive your road on public roads without a catalytic converter.

While it’s unlikely that a police officer will notice and ticket you for driving without one, they very well can.

Old, rusted catalytic converter

Moreover, if you live in a state that requires annual inspections, your car won’t pass without a catalytic converter.

That means if you plan to skirt the law and remove your catalytic converter and need an annual inspection, you’ll need to reinstall it every year to pass the inspection.

That also means re-tuning the engine each year, so it’s not a small amount of work for those nominal horsepower gains.

More disadvantages include an unpleasant smelling cabin, check engine light and error codes, droning exhaust, and an array of other problems that depend solely on the tune and the car in question.

Cat Delete Best Practices

Removing the catalytic converter is just a matter of unbolting it; the important part is what you put in its place. It’s common practice to replace the catalytic converter with a straight pipe or test pipe.

If you have a catted mid pipe installed from the factory, then unbolting it and installing a decatted aftermarket x-pipe or h-pipe is an option.

Or you can choose one that comes with a high-flow catalytic converter installed.

If you want to do away with the restriction without the hassle of driving around with the OEM catalytic converter, the high-flow cats are your best bet.

High flow catalytic converter

But if you intend to get a straight pipe fabricated or do it yourself, remember to orient the flanges properly when you weld them on.

It’s a good idea to install an O2 simulator to trick your ECU into thinking that you still have the OEM catalytic converter installed and that it’s working properly.

You will need to get a tune after removing your catalytic converter. If your car isn’t tuned for serious performance gains, the cat delete won’t do much.

One of the reasons behind that is the ECU uses information from the oxygen sensors from before and after the catalytic converter to fine-tune performance.

But without the catalytic converter present, the downstream O2 sensor is practically useless, and so the ECU doesn’t get an accurate reading.

The ECU will still try to fine-tune the performance, but it won’t do it the right way because it’ll get inaccurate information. Tuning your ECU fixes this problem and gives you the performance results you want.

Gutting a Catalytic Converter

Catalytic converter after gutting

So far we’ve focused on pros and cons and how to complete a catalytic converter delete, but that’s not the only option you have if you want all the performance benefits associated with a cat delete.

Another option you have instead of removing the catalytic converter is to “gut” the catalytic converter.

In short, this means hollowing out its insides and removing the honeycomb. That’s one way of getting rid of the restriction.

Of course, this also completely destroys the emissions function of the catalytic converter, rendering it functionally useless.

Gutting vs Test Pipe

The pros and cons of gutting a catalytic converter are a lot more complicated and debatable in contrast to a regular cat delete.

That’s because you’re creating a large hollowed-out resonating chamber for the exhaust to settle and bounce around in, instead of replacing it with a test pipe.

Before and after the removal of a catalytic converter

This will create a lot of turbulence in that part of the exhaust system.

The way around this is to run a straight pipe through the hollowed-out catalytic converter, but this creates a bit more work for you to achieve the same results as a cat delete.

However, one advantage that a hollowed-out catalytic converter has over a traditional cat delete is that it’s much harder for a regular cop to see what’s going on.

But it’s still completely illegal in all 50 states, and you won’t pass the inspection with a hollowed-out catalytic converter.

The long answer is that you can hollow out your catalytic converter if you want to reduce the chances of getting caught.

But to do it right, you need to complete a little extra work to add a straight pipe through the converter to get the performance results you want.

How to Hollow Out a Catalytic Converter

Because it’s illegal to hollow out your catalytic converter in the United States, it’s unlikely to find a professional shop that’s willing to do it for you.

If you’re wondering how to gut a catalytic converter without removing it, the short answer is that you can’t. You will have to uninstall it to finish the job properly.

The first step towards gutting a catalytic converter is to remove it entirely so you can get access to both the inlet and the outlet.

Once you have the catalytic converter out, take it to a workbench. Put it in a vice with one of the sides facing up, put in a long chisel, and line it up with the honeycomb pattern in the converter.

Cat-con gutting process with chisel

Tap the back of the chisel with a hammer and work the honeycomb interior down until it breaks apart. Work your way around the interior to fully hollow out the catalytic converter.

Because of the fine dust, you’re creating during the process we highly recommend wearing a respirator during this process to keep yourself safe.

Cat-con gutting process

If you’re not installing a straight pipe through the converter, then the procedure ends here. Just reinstall it from there and you’ve successfully hollowed out your catalytic converter.

But if you are wanting to install a straight pipe through the catalytic converter, then you need a pipe that matches the inner diameter of the outlet and inlet opening.

Ensure it is cut to the same length as the cat-con, then run it through the interior.

You want a pipe that fits snugly against both openings, that way the exhaust can’t work its way around into the rest of the converter.

Add a few spot welds to help hold it in place and take a look around both the entry and exit of the converter. If there are any openings, use a welder to fill them in.

Next, grind off the ends of the straight pipe until it’s flush with the converter entry and exit points.

Gutted, straight-piped-catalytic converter

Once it’s completely flush with the straight pipe inside the converter you can install it back onto your vehicle with the original mounting hardware.

If you complete this method properly you shouldn’t be able to see that the catalytic converter has been modified.

Concluding Summary

OEM cats installed

So now you know what happens if you remove your catalytic converter. It’s an easy way to add a few extra ponies without spending a ton of money.

But because it’s illegal in every state, you need to make your decision carefully. Either way, we say run a cat if you’re daily driving.

It’s your choice to make though, and if you intend on upgrading your car well beyond its OEM capacity, it’s only a matter of time before it’s no longer street legal anyway.

What do you think about this mod? Let us know how you’re going to go about it in by leaving a comment below.

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