Can a muffler affect gas mileage?

I often hear people talking about exhaust systems, mufflers and how they can alter power and increase gas mileage. The claims range from outrageous statements of large increases in horsepower to statements that it doesn’t make any measurable difference what so ever. So I would like to take this opportunity to disspell any uncertainty and clear things up once and for all.

How Exhaust Systems Work

First let’s think about how an exhaust system works. Hot, burnt gas is expelled from the engine after combustion. With out an exhaust system this gas would be pushed straight into our engine bay and likely be sucked up into the cabin. However there is a greater issue of the noise level that it would cause as well. An open hole to the cylinders where combustion and explosions happen is not going to be quiet. We wouldn’t want to drive our cars and no one would want to live near a street.

To fix these two issues an exhaust system was invented. Rather than the gas leaving the engine inches from the combustion, it is pushed through a series of pipes eventually out into the atmosphere behind the car. The pressure of the exhaust is what causes it to come out quickly. This pressure causes the expelling gasses to lose energy which reduces the sound but also reduces the effeciency of the engine.

How the Muffler can Affect Gas Mileage

Despite the fact that the exhaust pipes themselves cause a drop in energy and a reduction in sound, it doesn’t do a very good job at it. If you have ever herd a car with out a muffler you will understand what I mean. So to combat this noise problem further the muffler was invented. The muffler’s job is to reduce the energy in the gas even more so, often times causing the gas to work its way through a series of baffles, tubes, pipes, turns and other restrictions. These restrictions take more energy out of the gas causing the noise to dissipate.

These same restrictions cause the exhaust system to be less effecient, which means the motor is less effecient, which reduces gas mileage.

So the answer is yes, a muffler can affect gas mileage.

How much? Not a whole lot, in fact there are a lot of better ways to improve your gas mileage in significant ways that won’t cause your ears to bleed every time you go for a ride.