Do Mufflers Increase Horsepower: An Expert Weighs In

By September 1, 2021Muffler

Aftermarket mufflers / muffler delete do not increase horsepower by much. Muffler is too far back in the exhaust system and the reduction in backpressure is insignificant.

You can only gain minor horsepower if your stock muffler is extremely restrictive.

I personally tried using a muffler on my 2006 Honda Civic and it did not result in any significant horsepower gain.

For this article, I have spoken to my mechanic friend extensively. He’s a guy who has done it all – muffler deletes, turbo installation, tuning – you name it. This article summarizes his thoughts and opinions.

We will cover the following things: 

  1. How Does Engine Generate Power?
  2. Why Aftermarket Mufflers Won’t Add Horsepower?
  3. Does Muffler Delete Add Horsepower?
  4. 4 Better Ways to Increase Horsepower
  5. My Recommendations

So, let’s start!

How Does Engine Generate Power?

Every car is a combustion engine. Car mix air and fuel to create combustion and generate power to wheels

Modern gas engines use four main parts- cylinders, pistons, fuel injectors and spark plugs. Combining these parts make an incredibly powerful engine that converts gasoline into torque for the wheels.

One of the most important components in an engine is the piston. The piston does two things: it moves up and down and creates a vacuum.

This vacuum allows air-fuel mixture to enter the cylinder so that fuel can be burned with oxygen to produce power.

The power stroke is what powers the pistons up and down. This occurs when fuel undergoes combustion in a very controlled manner, creating heat and expanding gas.

The piston’s downward motion created by this explosion pushes on the fluid inside the cylinder which creates water pressure to boil and pressurize air for end of process.

We do upgrades like exhausts and mufflers to make the exhaust system less restrictive – allowing the gas to leave faster so more air can enter.

anatomy of combustion chamber

Car generates power by creating combustion using air and fuel. This combustion pushes down piston which translates into movement to your car wheels.

Why Aftermarket Mufflers Won’t Add Horsepower Much

Aftermarket mufflers won’t add a lot of power to your vehicle – the reduction in backpressure is minimal. An aftermarket muffler will add minor horsepower only if the original system was really restrictive.

Muffler is just a small component in the exhaust system, and it’s located at the very end of the car. Therefore, the impact on horsepower is minimum.

When it comes to aftermarket, modifying components that are closer to the engine will result in more power. For instance, headers, exhaust pipes, and downpipe can help increase the horsepower of an engine.

Excessive backpressure in the exhaust system is caused by a variety of things. Restricting exhaust flow will create excessive backpressure, and anything that does so will cause this problem.

Aftermarket mufflers do reduce backpressure. However, this is not enough to increase the horsepower.  

For instance, a straight through muffler has no restriction at all and reduces backpressure. At most you can gain 5 horsepower with straight through mufflers. 

Not enough. Right? 

If you want to reduce significant backpressure (enough to improve horsepower), you need to look into bigger exhausts, headers and even CAT delete. 

illustration of a car exhaust system

Generally, the closer the mod is to the engine, the more backpressure it can reduce. Muffler being way back won’t decrease backpressure by much.

 

Aftermarket mufflers are really used for sound improvement. If you want a much more aggressive sound, then muffler is for you.

If you solely want power, aftermarket muffler is not the mod. You are better off getting a downpipe or catback exhausts. I will discuss the alternatives later.

If you decide that an improved sound is what you want, then checkout a Flowmaster Super 40. It’s a performance muffler that has aggressive sounds but also not too loud.

Related Article: Best Muffler: Which To Get & What To Look For?

How Much Horsepower Gain From Muffler Delete?

A muffler delete adds only about 5-10 horsepower to your car’s engine. 

A muffler delete is a modification to the exhaust system that removes the mufflers and replaces them with straight pipe. This means less weight, and aggressive sound!

Also, mufflers are heavy parts of an exhaust system that can slow down a car.

Removing these parts will allow your engine to run a little faster (due to weight reduction) while also producing loud sound.

Which muffler is your car right now?

Related Article: Muffler Delete Vs Straight Pipe: Horsepower, Mielage & Damages

4 Better Ways to Increase Horsepower

1. Cat back exhaust

Cat-back exhaust systems are modifications to the exhaust pipe that improve airflow. Larger exhaust pipe means less backpressure and more power.

The system runs from the tip of the exhaust to the catalytic part of the system and is comprised of one pipe connecting a muffler and a catalytic converter, as well as an end for directing emissions out through.

A cat back exhaust system is a simple power modification that will free up your car’s exhaust gas flow and produce a more pronounced engine sound than the stock muffler.

A more restrictive catalytic converter will limit the amount of power gained from a cat back exhaust system.

A cat back exhaust might not seem like the most important upgrade to your car but adding one can increase horsepower.

Aftermarket exhaust systems are designed to be more open than your stock exhaust, interrupting less of the engine’s airflow.

These changes can result in reduced back pressure at the engine manifold, meaning that the engine can breathe easier and produce more power. 

A cat back exhaust system can offer a significant increase in horsepower when the stock exhaust restricts too much airflow.

Opening up airflow changes the power band of your car, resulting in an increase in horsepower.

In this case, you might observe horsepower gains of more than 10 HP.

Cat-back exhaust systems for a car range from $300 to $1200. Factors such as the quality of steel and mufflers will affect the final cost.

Installing a cat-back exhaust system costs between $75 and $100. Local retailers may offer to install it for free if you buy the exhaust from them.

In all 50 US states, cat back systems are legal. However, you should check your local laws before buying one.

Related Article: Best Exhaust: Which To Get & What To Look For?

Image of Axle Back Exhaust

Aftermarket exhausts are great for horsepower and sound.

2. Downpipe

A downpipe is a tube that directs exhaust gases from the turbo into the exhaust system. The less restrictive it is, the harder exhaust gases can flow and spool the turbo.

NOTE: A downpipe only works with turbo cars. So make sure your car has turbo before considering an aftermarket turbo.

Installing a downpipe is an excellent option for drivers who want to maximize their car’s power at every RPM.

While installing one will create a noticeable increase in the turbo’s output, even if it’s just 40-50 horsepower, there are still more benefits of a downpipe.

A downpipe will cost you around $350 and installation cost will be around $200. Installing it yourself is also an option. Though, it could get a bit difficult because there’s not much space to work with.

Therefore, it is recommended to ask a mechanic to install it. 

Aftermarket downpipes are not street-legal because they have less restrictive catalytic converters – which can increase emissions (but great for horsepower).

Ensure that you ask specifically for the state in which your vehicle is registered. Some states prohibit certain modifications to a car even if it was obtained elsewhere, while others have no problem granting such requests.

Stock downpipe Vs Aftermarket downpipe. Notice the aftermarket is wider, have lesser bends and is made of high quality aluminum.

3. Headers 

An exhaust header is a pipe that connects to the engine’s exhaust manifold and runs to one or more mufflers.

The purpose of this system is to reduce back pressure, which increases power output for the engine.

Exhaust headers are designed to collect exhaust gases that come out of the engine and merge them into a single flow. They are made of thin stainless steel and have equal length – this allows for optimal efficiency with exhaust gases.

An Exhaust Header adds about 15-20 horsepower to your car’s engine. 

Exhaust Header improves HP by helping the engine evacuate the exhaust fumes that it has to push out.

It will cost you around $700. The process of installing an exhaust header is really difficult. I would recommend you ask a mechanic to install it for you.

Headers aren’t always illegal, some vehicles come stock with them, and most short tube headers are considered legal in most states. 

Long tube headers on the other hand are a bit of a different story. Not only will they make your vehicle louder, but it is also considered tampering with your vehicle’s emissions, which according to the EPA is illegal under federal law.

Exhaust Header And Manifold

Aftermarket header vs stock header. Notice the aftermarket headers have uniform lengths, is wider and is made of high quality aluminum.

4. Turbo (or bigger turbo)

Adding a turbo to a car’s engine is a highly effective way of massively increasing its power.

In simple terms, a turbo forces more air into the engine’s cylinders which, added to some extra fuel, means a bigger bang can be created in the cylinder.

A bigger bang means more power.

An internal combustion engine works by drawing in fuel and air. That mixture is ignited to produce power, but the exhaust gases are also produced and are forced out of the system. In turbocharged engines, the exhaust gas is reused.

A turbocharger works with the exhaust system. Ultimately, it forces air into your car’s engine which facilitates an increase in power.

Depending on the specific model, a turbocharger could give you 70-150 pounds additional horsepower.

The cost of the turbocharger will depend on make and model but can start at around $400 with labor costing an additional $150-$200.

As long as your car passes your state’s emissions check and physical safety inspection, you’ll be allowed to equip it with a turbocharger.

Therefore, you should check your state laws before buying a turbocharger. 

Image of turbocharger

Turbo sucks air from the outside. compress it into high pressure ball and deliver it to combustion chamber for extra power due to bigger combustion.

My Recommendation

Aftermarket muffler is used only for sound improvement and not for horsepower gains.

Therefore, I would recommend you buy the Flowmaster Super 40 muffler for sound improvement. This muffler is not so loud yet very aggressive. 

Here’s an article I wrote about the Flowmaster Super 40. Best Muffler: Which Muffler To Get & What To Look For?

However, if you are looking to gain some power, I would suggest using a downpipe for turbocharged cars. 

A downpipe is cheap and can give you up to 50 horsepower. 

I would recommend going for a cat-back exhaust system if you are using a non-turbo car. It is recommended for beginners.

A cat-back exhaust system will help you improve the power, sound, and the looks of your car.

Ifandi S.

Ifandi S.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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