Modern exhaust layout and function

Let’s take a moment to talk about your car’s exhaust system. Unless you’re into a full aftermarket exhaust swap, it’s probably one of those out of sight, out of mind sort of things. It doesn’t generally require and cleaning or maintenance, and when parts wear out or break, you simply replace them. But, just because it doesn’t require ongoing attention doesn’t mean it isn’t an active part of your car.

What does your exhaust system do? Well, if you said that it carries exhaust gases safely away from the engine out of the way of the cabin and provides noise control for the engine, you’d be right, but only partially right. These days, the modern exhaust is more an active part than ever. Let’s examine a typical system piece by piece.

Modern fuel-injected gasoline cars are more dependent on their exhaust for proper operation than you might initially think. While the header(s) coming off the exhaust manifold are pretty much the same as ever, these days they’ll feed into the first of two (or, the first two of four, in the case of dual exhaust systems) catalytic converters. As the name suggests, catalytic converters contain catalyst materials, which act to break down exhaust gases into less harmful emissions. Although arguably not a part of the exhaust system itself, and rather a part of the emissions system, the front oxygen sensor measures exhaust gas composition and feeds that information to the engine control unit (ECU) in order to vary fuel and air to reduce harmful emissions.

There may or may not be a separate pipe exiting the front catalytic converter. From there, it will enter a rear catalytic converter which further break down the remaining exhaust gases and once again, provide feedback to the computer through the rear oxygen sensor. From there, the exhaust exits the rear converter and finally passes through the muffler, which, as always, dampens sound, reducing noise pollution.

While there are a good number of factory and aftermarket options for exhaust systems, it’s important to note that not all catalytic converter parts are 50-state legal. The big exception, of course, is California. So, if you live there, make sure that the exhaust parts you buy are legal in your state. Also, it’s important to keep in mind that if your car is old enough to be grandfathered out of emissions inspections, it’s not legal to completely remove them for any reason, as this is prohibited not by state, but by federal law.