Exhaust manifolds, catalytic converters, mufflers and pipes -- is it all necessary? Absolutely! The four-stroke internal combustion engine is a giant breathing machine. Air and fuel are taken in and ignited; this generates the power stroke, propelling the engine forward. Burned exhaust gases are then pumped out and carried away via the exhaust system. Simple, right? Not so fast! Here's a description in detail.

First of all, the exhaust manifold provides an easy, durable way to exhaust (vent) hot gases from the combustion chamber. These components are usually cast out of iron to stand up to blistering exhaust gas temperatures and are compact in size allowing maximum engine compartment space. Finally, the manifolds are tuned. Tuning is a process used in the manufacturing of exhaust parts. In this process, the exhaust part is designed to provide the smoothest, free flowing, yet slightly restricted passage for the gas to escape. The design causes a phenomenon called the "venturi" effect -- or the speeding up of air flow. This allows the engine to breathe responsively as the driver accelerates and decelerates, optimizing engine performance.

To better understand the "venturi" effect, look at the operation of a typical garden hose. When the hose is hooked up to the spigot without a nozzle, what happens when the water is turned on? Water comes out right? Now, try reaching the other side of the yard with that stream. It's not going to happen! To reach the other side of the yard, a restriction is introduced into the system in the form of a hose nozzle. The same principle applies to the car's exhaust. A little bit of restriction is necessary to optimize engine performance.

All the components in the exhaust system are tuned, including the exhaust pipes. Mufflers and resonators are designed to quiet the sound of the engine's exhaust, which can be quite abrasive if allowed to be uncapped. The mufflers and resonators have baffles or passageways built into them for the exhaust gases to follow. Routing the gases in this manner produces a muffling effect, quieting the noise of the engine's exhaust.

Catalytic converters are designed to lower exhaust emissions. They work by creating a chemical reaction or catalysis (hence the name catalytic converter). The converter is filled with a chemical agent called a catalyst that heats up to cherry-red when hot exhaust gas flows through the converter. If any unburned gases (or hydrocarbons) are present in the exhaust flow, a catalysis takes place, burning up these gases and thereby cleaning up the exhaust emissions. Problems occur when the engine's performance system is malfunctioning. When more unburned gas is filtered through the catalytic converter than it is able to burn, an interesting phenomenon takes place. This gas fuses with the catalyst forming a blockage in the converter. Exhaust flow is cut down drastically and the car loses power. Sometimes the car emits a pungent odor out of the exhaust pipe that smells like rotten eggs, which is due to either the type of gas being used or a maladjusted fuel mixture.

It is very important to keep your car's performance system tuned, so that the engine will run at peak efficiency with the least amount of exhaust emissions.

Previously we established that it is important to have an exhaust system that has slight resistance (or back-pressure) for optimum breathing response. That is the state of being "in tune." What happens when a restriction is introduced into the system due to a collapsed exhaust pipe, clogged catalytic converter, or plugged muffler? Well, as Dennis Hopper would say, "BAD THINGS, MAN!!" Airflow is affected and the computer goes crazy trying to compensate for the malady. Transmission shifting, electronic engine controls, fuel delivery, and emission systems are negatively affected, not to mention the possibility of fire from overheated exhaust components, as well as the burning of the engine's exhaust valves due to excessive exhaust back-pressure.