Exhausts Cutout 101: Loudness, Installation, Legal & Horsepower

Exhaust cutout is a free opening in your exhaust system. It is a device that is installed in between headers and muffler – to control the loudness of your car at will and gain minor HP depending on the size of your engine.

When the cutout is closed, exhaust gasses pass through the normal pathway but once the exhaust cutout is open the gasses pass from the headers to the cutout without entering the muffler making the car sound loud.

As far as the loudness of the cutout is concerned it depends on how much you open the exhaust cutout if you partially open it then it will enhance the sound up to a decent level but once it is fully open it will act like a muffler delete and exhaust sound will be at its maximum potential making it a lot louder.

I tried the exhaust cutout once in my Toyota Corolla 1981. . It was a great experience as it used to be my daily so I wanted it to be quiet for most of the day. But when I wanted to have some fun with it all I had to do was click a button and all the fun was there.

This article is a complete guide for those who are thinking of trying it with their car and finding some answers like what exactly is exhaust cut or is it legal or not. All of your questions will be answered in this article.

Exhaust cutout is a free opening in between your headers and muffler that you can open and close at will. It allows the exhaust gasses to bypass the muffler and enter directly into the atmosphere making your car loud.

It is mostly a “Y” shaped pipe with one end connecting the exhaust headers with the muffler while the second end remaining free open. It has a flap inside it that is connected to an electric motor that opens and closes when the key is pressed from the fob.

But there are some more advanced exhaust cutouts that are integrated in the muffler and they replace the muffler. 

They work in such a way that when the flap is closed the gasses pass through the muffler system making the car soundless and when the flap is left open the gasses bypass the muffler chamber and pass and exit directly into the environment making the car sound louder.

Usually these are installed to make the car sound louder whenever you want it to be loud. Otherwise, it remains quiet or at factory settings. It is great to have the exhaust cutout installed in your daily to have it quiet as well as a fun to drive car.

The internals of exhaust cutout. When the flap opens, exhaust bypass the muffler and will make your sound sound extremely loud.

When fully open, the exhaust cutout makes your car a lot louder as compared to your stock exhaust system. 

The reason behind this is all of the exhaust gasses are bypassing the muffler and entering directly into the atmosphere. It’s just running your car with a muffler delete and you can guess how much louder it will be.

It’s exactly like running a car with a straight pipe exhaust system with no muffler and resonator but in this case, you have a choice when you want it to be louder. 

It also depends on the engine setup you are running if you have a big block or a V8 its definitely making a huge difference. Even a 4-cylinder engine will also have a huge impact on sound.

Installing an exhaust cutout is pretty easy as it comes with a complete package from the factory. You don’t need some special tools for the installation.

Installation is easy and can be a DIY project if you have enough knowledge. Usually, the package has all the accessories that are required. The package mostly involves cutout, electric module, key fob and some wiring with clamps. Step by step guide for the installation is as follows

1. Make a cut in the exhaust length according to the length of the cutout before the muffler
2. If you want a weld free setup, just put the exhaust cutout inlet onto the exhaust pipe and clamp it tightly 
3. Do the same procedure with the exhaust cutout outlet.
4. Now connect the exhaust cutout wiring with the module that came with the wiring. you can place the module anywhere in the car.
5. Connect the module with the positive and ground cables.
6. Turn on the car and press the key fob button it will start working 

You can place the key fob anywhere inside the car wherever you want.

Now all you need to do is just click the button and your engine will talk when you rev up.

There is another type of exhaust cutout that is not mostly seen. It’s called vacuum actuated exhaust cutout. It does the same purpose but here the flap is vacuum operated. People install these because the motorized exhaust cut out stops working due to excess heat of the exhaust gasses.

 Usually, it happens with the cheap exhaust cutout. All the installation process is the same as the electric exhaust cutout except in the vacuum actuated there is a vacuum line that goes from the module to the flap instead of electric wire.

Here’s a great YouTube video that shows how to install exhaust cutout (It needs cutting and welding!)

It’s not legal to have an exhaust cutout in the vehicle. But the rules may vary from region to region 

 In USA and UK, it is illegal to have an exhaust cutout or any alterations in the exhaust system that produce excessive noise or against the emission standards of the laws.

So, you can only have it only for track but these kinds of mods are not road legal. In certain areas of the world u need to have license for these mods.

These laws change from county to country so u can check the law status of your country by visiting the concerned authority’s office or website.

Installing an exhaust cutout to your stock exhaust system can increase the horsepower and torque.  The horsepower gain entirely depends on the engine displacement of your vehicle. 

The bigger displacement you have the more gain you are going to get. For regular cars below 300 horsepower, I wouldn’t expect any significant horsepower gain.

To understand the process behind it we need to understand the working of the engine and exhaust system. 

When the ignition stroke is completed, the gasses produced in the engine need to be released. If the gasses are released quickly from the block, then it helps the intake stroke to happen a little quickly. 

Now if the gasses remain inside the block for a longer period of time this will cause difficulty for the intake stroke and you will lose power. But if it happens on time or a little earlier then definitely it is going to give you more power. It also shortens the pathway that causes the gasses to release quickly.

This process increases the horsepower and torque and also you don’t need special type of tuning or any upgrades to the engine. But the horsepower gain entirely depends on the engine displacement.

If the car has a bigger displacement like a V8 or V6 with a turbo the difference will be noticeable and it’s easy to extract 10-15 horsepower. With the smaller engines up to 5 horsepower gain is seen.

Now if you don’t notice any horsepower gain on your stock exhaust system even after the exhaust cutout installation then you need to change the headers to aftermarket headers for better flow rate. 

If you are already using wide headers, you are going to notice more change. The reason behind this is sometimes vehicles from factories come with a narrow headers and exhaust system that doesn’t fulfill the requirement and that’s why you don’t notice any significant change in the horsepower and torque.

Related articles:

1. Do I Need A Tune If I Get Exhaust Headers?
2. Long Vs Short Tube Headers: Horsepower, Sound, MPG & Tune

Exhaust cutout won’t cause any harm to the engine. As it is not blocking the exhaust gasses or any sort of blockage in their way so it does not cause any harm to engine.

The exhaust cutout is providing a free passage to the exhaust gasses and helps the release of gasses conveniently so not causing any damage to the engine.

You must keep a check on the engine’s air fuel mixture ratio to check the performance of the engine. If your engine is running rich in fuel, it causes the unburnt fuel to enter in the environment that in not only harmful for the engine but also for the engine health as it causes deposits of the carbon on the spark plug tips and the burning is not efficient or up to the mark so you will lose power.

So, there must be a balanced ratio of air and fuel to protect the environment and gain maximum power from the engine.

Exhaust cutout will not harm your engine. It only directs the exhaust gases to bypass the muffler.

Exhaust cutouts are reliable. If you buy exhaust cutouts of the good company they last longer and are reliable.

Depending on the material and company that made them there is a huge variety of exhaust cutout. If the material they are made of is good enough to hold the pressure of the exhaust gasses and the motor is made of good material and can hold enough pressure the yes, they are reliable.

The qualities that made an exhaust cutout reliable are minimal to no leakage and the material. As leakage from any point causes the oxidation of the material and hence leading to rust of deterioration of the metal that is a failure for exhaust cutout. 

You must also be very careful while installing if there is a leak or any gap remains it is going to cause a problem in future.

If you use some cheap exhaust cutout it may give you trouble like leaking or flap jammed. so, in order to keep the damage minimum, we must be very careful in choosing the perfect exhaust cutout for our vehicle.

You should use exhaust cut out only  if you regularly visit the track or your state has some leniency with vehicle sound laws. 

If your car is a daily driver and you are only driving on the roads, then I don’t recommend an exhaust cutout because it can get extremely loud and get you in trouble with the local traffic police.

After all the discussion we have done above it is fair enough to conclude that exhaust cutouts are the solution for the cars that are used daily as well as a track runner.

You can make it quieter and road legal as well as let it roar on track by just clicking a button. No other major mods or preps are required so it saves a lot of time and effort for the owner.

As far as the reliability and Maintenance is concerned you need no maintenance for it and also if you use a good one for your car it’s pretty much reliable and makes no issue at all. So, if you want to have fun with your daily then surely exhaust cutout is the solution for you.