Is Having No Back Box Illegal?

Do you have no back box, and you’re scared to go out that way because you don’t know if it’s illegal or not? Then, we know you’re likely to ask the question — Is Having No Back Box Illegal? In this article, we’ll give you an answer to that question and more details about the “back box.”

Is Having No Back Box Illegal?

It’s illegal if it’s too noisy, which it probably will be if you have no backbox. It’s nothing serious, though the police will just give you an order telling you to replace it which you’re going to do anyway. Police tend not to do anything.


What is the exact function of the exhaust back box in the engine? What it takes is the fast and hot moving gases, produced by the process of combustion and also, works in slowing them down. This exact area is quite important as regards the running of a quiet and smooth vehicle. Without surprise, the very first sign that’d tell you that there exists problems around this area is an increase — noticeable increase — in the exhaust’s volume. You’re also likely to experience a couple of vibrations than what you usually experience when you are controlling the clutch of the car. And, there could, as well, be — in the fuel economy — a change.

It’s undoubtedly a pretty cumbersome process when it comes to replacing the exhaust back box, and it’s also a wise idea to have it done by someone who has the experience to handle such. Before you can begin to carry out the processes, you have to have in your possession the following tools:

  • Carjack and two jack stands
  • Hammer
  • Saw
  • Spanner or socket set

1. Prepare Your Vehicle

Before you start going over the process of the replacement, it’ll be required of you to jack up the car on a dry, hard and level surface. Ensure you jack up the back of the vehicle and fit in a jack stand on each side of the car in order to give support to its weight. This will give you the needed access to the exhaust back box.

2. Locate The Exhaust Back Box

Get a backboard and use it to slide under the car and search for where the exhaust back box is located. Usually, this is found in the middle of your vehicle’s catalytic converter and the rear axle. Once you’re in the know of where the silencer is, pick up your spray — which contains a lubricant — and apply it on the fixing nut. As these can be found under the car, the chances are they’ll be partially affected or rusted by dirt, making it difficult for them to detach.

3. Remove The Exhaust Back Box

Make use of a spanner or a deep socket for the purpose of using it to fix bolts that firmly hold the exhaust back to the car. These are likely to take a quite considerable amount of energy and effort, and if you are experiencing trouble, try getting more lubricant and after making use of it waiting for when it takes effect. At the time when you successfully detach the bolts, pick up the saw and use it to cut away the exhaust pipes immediately — behind and in front of the silencer. Finally, it’s not time to take out the hanger — the one that holds the silencer in place.

4. Attach The Exhaust Pipes

You have to perform the act of smoothing the ends of the exhaust pipe carefully. Also, slightly split them in order to allow them to split into place on the backbox. The next thing to do is, side clamps up the pipe’s both ends and ensure you apply a liberal touch of sealant. At this point, you should have the ability to slip the silencer onto the exhaust pipe ends and make sure the clamps are moved into place.

5. Bolt The Back Box To The Car

Now that you have the exhaust pipes, both exhaust pipes, firmly attached to the back box, it’s time to use the hanger to reattach the part to the car. Pick up the original bolt and afterward, use the spanner or socket set to tighten every one of them in place, and finally, what you’d have to do is: do what’s possible to ensure that the various clamps are completely tightened around the in and out vents on the silencer. Once you find out that you’ve achieved satisfaction with their placing, take the car off the jack stands.

As with the numerous mechanical work, once you’ve carried out the process of replacing the back box, you will want to take the car out in order to run a short test drive. If, at this point, you still observe that the exhaust still creates unbearable noise, then go back and take a look at the seals and the fixings on the back box to ensure that all of these are properly held in place.

You might be wondering, “what is a catalytic converter?

Catalytic Converter

We are all aware of the fact that exhaust gases are a pollutant, and they also contain a few substances that are pretty unpleasant. The task of the catalytic converter is to conduct the conversion of toxic gases into less toxic gases. What does it feature? It features a structure that looks like a honeycomb — which works in increasing its surface area. The catalysts that are present within the converter amazingly break up nitrogen oxides into nitrogen and oxygen. The interesting thing about this is, the moment nitrogen oxides get split into nitrogen and oxygen, they become completely harmless.

They, then, ensure that carbon monoxide is converted into carbon dioxide — and finally, they’re responsible for the conversion of unburnt hydrocarbons into carbon dioxide and water. As for the result, its emissions that while not totally harmless, are less harmful than the gases entering the converter. There’ll also be something called lambda sensor, it’s mounted to the pipe which gets access to the cat.


Whenever you drive your vehicle, the exhaust moves — which is the reason why the engine mounts make movement possible. If the setting was that the exhaust has to be bolted directly to the underside of the car, the engine’s movement could easily crack and cause damage to the exhaust. In order to ensure that this is prevented, exhaust systems are suspended via a series of rubber hangers. These can, most times, fail before the exhaust, so it’s quite worth it to be checking that of yours periodically.

Frequently Asked Questions (FAQs)

Can You Drive Without An Exhaust Back Box?

Yes, it will be running weak. That is not good. Running rich is not dreadful but running weak leads to the engine running too hot and you may burn out valves or burn holes in the tops of pistons. Not recommended.

Is A Back Box A Silencer?

At the car’s rear — the place where the exists — there’ll commonly be a back box silencer with a tailpipe, or tailpipes connected to it. Often, this is connected directly to the center section through a sleeved fitting. The size and design of the tailpipes have what it takes to alter the sound produced by the exhaust system.

Will Straight Pipe Pass Emissions?

Registered. Straight pipes as in no cats or straight pipes as in no mufflers? Mufflers are not a smog check item, anything behind the catalytic converters on the car are not considered emissions components and can be changed at will. (As long as you stay under the sound limits dictated by local ordinance…)

Does Back Box Improve Performance?

A muffler is at the very end of the exhaust, which is why performance effects are marginal with any sort of muffler swap. It’s all about sound at that point. Headers on the other hand offer huge performance benefits, due to the proximity to the engine and alteration of emissions equipment.

Can You Legally Sell A Car Without A Catalytic Converter?

Driving a car without a catalytic converter is illegal unless the age of the vehicle is exempt. The car will not pass emissions test. It is illegal to sell a car with a tampered emissions system.

What Is The Standard Back Box Size?

Sizes available are 1 gang (Single sized) or 2 gangs (Double sized), with depths available being 25mm, 35mm or 47m. The UK Standard size is usually a 35mm depth of the back box and this will be suitable for most switches and sockets.

Is A Back Box Delete Illegal UK?

It is not illegal, it does not affect the emissions as that is what a cat or dpf is for. A mid box (resonator) or back box is for resonance only which means noise reduction only. Yea if your car is very loud and police class it as causing an issue, they can advise you to change it and reduce the noise of the exhaust.

Is Having No Back Box Illegal – Conclusion

As a recap of the response we gave to the question — Is Having No Back Box Illegal? — we stated that:

It’s illegal if it’s too noisy, which it probably will be if you have no backbox. It’s nothing serious, though the police will just give you an order telling you to replace it which you’re going to do anyway. Police tend not to do anything.

Thanks for reading.

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