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Does A Muffler Reduce Horsepower?

Every petrolhead wants to maximize the performance of their car. This can easily be achieved by starting with the exhaust system. So, installing a muffler will improve the engine’s sound, but does a muffler reduce horsepower?

A muffler will not reduce horsepower as it allows the exhaust gas to flow out of the cylinder quicker. Some aftermarket mufflers may be more restrictive if used on vehicles with smaller diameter pipes. An aftermarket muffler is only one part of a performance exhaust system.

Read on to discover if a muffler will increase or decrease performance, the different types of mufflers and how to choose the correct one.

Will A Muffler Decrease Horsepower?

The primary goal of an exhaust muffler is to (as the name suggests) muffle or reduce the sound of the engine. Cars have specifically designed mufflers installed when they leave the factory. This is so that the vehicle can comply with noise regulations.

The muffler does also play a small part in the car’s performance. As the engine revs higher and produces more power, it produces more exhaust gas.

This gas must exit the engine, through the exhaust, and out the muffler. So, as the escaping gas leaves the engine, it is restricted by the standard muffler, which reduces the engine’s power.

But, this restriction is necessary to create sufficient back pressure in the exhaust system. The back pressure aids in engine scavenging, allowing more air to be sucked into the cylinder due to the exhaust’s vacuum (back pressure).

This is not very important in small compact engines and only becomes a factor in high-power performance engines.

So, a standard muffler only slightly decreases engine horsepower, but it is required by law to have a muffler installed on a vehicle. Several aftermarket mufflers can be installed that may be somewhat less restrictive.

But the muffler is typically a device that will change the engine’s sound. If you want to increase horsepower, a complete performance exhaust system will be required.

Will A Car Perform Better Without A Muffler?

When the muffler is removed from the exhaust system, it will slightly reduce the restrictions making the exhaust gas escape quicker.

But many other components in the exhaust system will still cause restrictions. So the biggest performance benefit of removing the muffler is purely in the loud sound that will resonate from the pipe.

The sound that comes out of the pipe will be similar to the sound that arises when there is a hole in the muffler. The sound may be suitable for certain people, but it will just sound like a broken exhaust muffler to a car mechanic.

If the car has a performance exhaust system installed that does not require a muffler, it is known as a muffler delete.

This exhaust system still uses similar components to a standard exhaust but relies purely on the resonator to give a uniquely loud sound. The system uses higher-diameter straight pipes to move the exhaust gas out of the engine. 

A straight pipe exhaust system is best used on larger engine capacities, as it will not be very effective on smaller engines. This is because the wider pipe requires a high gas velocity which smaller engines cannot deliver.

How Much Horsepower Will An Aftermarket Muffler Add?

Aftermarket mufflers come in two variants, fitted or bolt-on. The bolt-on muffler is easy to install but offers no performance benefit.

It may actually reduce performance as it may provide more restrictions to the exhaust system. The bolt-on mufflers are not great for weight saving, but they will give a deeper engine sound.

When a performance muffler is installed on an exhaust, it is commonly part of a complete cat-back exhaust system. A cat-back system means everything from the back of the catalytic converter to the muffler. This will include the muffler, mid-pipes, and resonator. A full-performance cat-back exhaust system may increase horsepower by up to 10%.

When the performance muffler is the only upgrade that is being done on the exhaust, the increase in horsepower will be minimal, if any. The sound that the performance muffler provides may be the only change besides the aesthetic look of the back of the pipe.

Will A Muffler Affect A Car’s Fuel Economy?

A performance muffler and exhaust system can improve a car’s fuel economy. This may be a very small improvement, but over a few thousand miles, the savings are worth it.

The performance muffler allows the exhaust gas to escape from the engine with fewer restrictions which benefits the fuel economy.

How To Choose The Correct Muffler

Choosing the correct muffler for your vehicle is essential if you want a slight power increase and a great sound.

The following should be considered before selecting a performance muffler.

The Exhaust Inlets And Diameters

Before choosing a muffler for your car, the following questions need to be answered.

  • Is it a single or dual exhaust system, as this will determine how many inlets the muffler will need?
  • What is the exhaust pipe’s diameter? This is important at the muffler must have the same size inlets.
  • How much space is available under the car for a muffler? There should be sufficient clearance so that all the fittings will fit in easily. This will also determine the shape of the muffler that can be used.

The Muffler Style

There are three main types of muffler styles, each with its drawbacks and benefits. The styles are:

Chambered Mufflers

A chambered muffler is ideal for road cars as they reduce noise and give a deep throaty exhaust note.

These mufflers have a series of chambers inside them that are set to specific lengths to reflect the sound waves against one another.

This will cause the sound waves to cancel each other out. The exact sound will be determined by the engine size and the number of baffles installed in the muffler.

Turbo Mufflers

Turbo mufflers use a set of perforated tubes that are set in an “S” shape to guide the gasses through.

This muffler is slightly more restrictive than the chambered muffler. The “S” shape tubing allows the gasses to travel through the tubing for longer, further reducing the noise.

The turbo muffler is ideal for road cars. The muffler may have additional options or levels offering more sound-deadening material. The Turbo muffler delivers a quieter sound at low RPMs that builds as the power increases.

Straight-Through Mufflers

These mufflers allow for maximum gas flow. Straight-through mufflers feature a straight, perforated pipe wrapped in a sound-deadening material such as fiberglass.

This type of muffler is best suited to high-performance racing engines, as they are extremely loud.

The Muffler Construction

Muffles are typically manufactured in a three-layer body construction consisting of the insulating layer, the inner casing, and the outer shell. The muffler must be durable and robust to handle everyday road debris and must be corrosion-resistant.

This leaves consumers with two choices when it comes to construction materials. The choices are aluminized steel, the cheaper option, and the longer-lasting stainless steel option.


A muffler does slightly reduce horsepower due to it restricting the exhaust gas, but it is more commonly associated with the sound the engine produces. If a complete cat-back exhaust system is installed, it will slightly increase a vehicle’s horsepower.