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Can You Replace Catalytic Converter With Flex Pipe? [ Answered ]

Can You Replace Catalytic Converter With Flex Pipe? [ Answered ]

As a car owner, you might need to replace your catalytic converter in some situations. This could be either due to a cat converter theft or because the existing catalytic converter has become faulty.

However, buying a new cat converter is an expensive investment, and you may not have the budget available at the moment.

You might be looking for a temporary solution until you can replace the cat converter with a new one. Well, a flex pipe can work as a temporary placeholder, but there are certain problems.

Can you replace the catalytic converter with a flex pipe?

A quick answer to this is that you can replace a damaged or stolen catalytic converter with a flex pipe.

Since a flex pipe is similar to or the same as the exhaust tubing itself, you might have been wondering if you can replace your cat converter with a flex pipe.

In fact, if your catalytic converter seems to be faulty, a good way to check is to replace it with a flex pipe temporarily. If your car runs better after the replacement and the symptoms are gone, it means you need a new cat converter. As cat converters are costly, it is a good idea first to check this way whether you actually need a replacement.

However, driving a car without a catalytic converter is illegal, and there are other downsides to using a flex pipe too. While you can surely use a flex pipe as a replacement, this should only be a temporary solution.


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How to replace a catalytic converter with a flex pipe?

To help you, we have developed a step-by-step guide on replacing a cat converter with a flex pipe. However, let us first check out what tools you’re going to need:

  • Sledge Hammer
  • Pipe Cutter
  • Hydraulic Jack
  • Sawzall Saw
  • Adjustable Wrench
  • Welding Machine
  • Ratchet Wrench

When you try to replace the component with a flex pipe, make sure to adhere to the prescribed means.

Step 1: Get your vehicle to a level surface to stay balanced and stable.

Step 2: Use the hydraulic jack to raise your vehicle, and the jack stands to support it.

Step 3: First make sure that the vehicle has cooled down. Then, slide underneath it and spray penetrating fluid on the cat converter.

Step 4: Dislodge and remove the oxygen sensor using an oxygen sensor socket and a ratchet wrench.

Step 5: The penetrating fluid should loosen up the mounting bolts. Unscrew them using an adjustable wrench. Lower the cat converter down to the ground.

Step 6: (Alternative) In case you find your catalytic converter welded to the exhaust system, you will have to cut it out instead.

Step 7: Take the flex pipe and fit it into the exhaust system, in the void space where the cat converter used to be.

Step 8: Lower the hydraulic jack by adjusting the jack stands.

Avoid touching the exhaust pipe while it’s hot, as it can result in painful burns. Also, wear gloves and safety glasses for protection when replacing the cat converter with the flex pipe.

Pros of using a catalytic converter with a flex pipe

Although it isn’t ideal, using a flex pipe in place of the catalytic converter has several benefits. These include:

1. Better mileage

Flex pipes help remove the exhaust gasses much faster than a catalytic converter. As a result, there isn’t any pressure buildup, and in turn, no back pressure towards the engine.

As the engine doesn’t receive as much strain as usual, it can work more efficiently. This results in higher gas mileage and would help you save fuel.

2. Increased engine performance

As the engine doesn’t face back pressure from the exhaust gasses, it can function more smoothly. This allows it to deliver higher horsepower than when using a catalytic converter. The operating temperature of the engine can also undergo a drop.

3. Affordable

Flex pipes are much cheaper than catalytic converters. This makes them an affordable replacement, albeit temporary. Even if you can’t afford a new cat converter at the moment, you can still drive your car by installing a flex pipe.

4. Healthier exhaust sounds

You’ll also notice a change in the note of the exhaust noises upon replacing the cat converter with a flex pipe. When a catalytic converter burns unburned gasses, the noises aren’t very healthy. This changes when you replace the cat converter with a flex pipe.

Cons of using a catalytic converter with a flex pipe

As mentioned earlier, using a flex pipe instead of a catalytic converter also has several disadvantages, such as:

1. Legal hurdles

Driving without a catalytic converter is not even legal in the first place. In fact, even removing your catalytic converter yourself is against the law. You could be facing hefty fines if caught while driving with a flex pipe instead of a cat converter.

2. Fault code

When the ECU detects missing catalytic converter, it triggers a fault code and turns on the check engine light.

3. Higher emissions

Without a catalytic converter, your vehicle’s emissions would be much higher and more toxic than usual. Besides releasing poisonous gasses into the atmosphere, this can also cause your vehicle to fail emission tests. It will most certainly fail MOT and inspection tests as well.

What can I use to replace my catalytic converter?

The best replacement for a catalytic converter is a new component of its type. You may also buy a used cat converter if it is compatible and in good condition.

Other cheap alternatives include flex pipes, straight pipes, and dummy cats. However, keep in mind that all three are illegal replacements for cat converters in the US, and you may run into trouble if caught.


While you can replace your catalytic converter with a flex pipe and enjoy several advantages, we do not recommend it as a long-term solution.

This is largely due to the laws in the US, which strictly prohibit driving without a cat converter. However, if you need a temporary solution and plan to install a good cat converter soon, you may go ahead.