Exhaust Knowledge

This guide is intended to provide you with a basic understanding of how to replace exhaust system components; not to provide in-depth knowledge of engine operation or exhaust systems. It will assume that you are familiar with the basic components of an exhaust system such as a muffler and the various exhaust pipes. It will be necessary to lift the vehicle in order to gain access to the exhaust system and there are often circumstances where a professional hoist is necessary. Use extreme caution to ensure your car or truck is properly supported at all times. Thoroughly examine the exhaust component to be replaced to be sure you will have the required space to remove it and replace it if you are limited to lifting the vehicle with jack stands. For this reason, this article will focus primarily on replacing mufflers and tailpipes which can usually (but not always) be replaced without the use of a professional hoist. Remember that exhaust gases are harmful and can be lethal and never work on the exhaust system while it is running and never run the vehicle in an enclosed area. Also, the exhaust system can get very hot while the vehicle is running. Always let the vehicle cool down sufficiently before beginning any exhaust repair.

Exhaust Systems

An exhaust pipe is connected to the manifold or header to carry gases through a catalytic converter and then to the muffler. In basic exhaust systems on "V-type" engines the exhaust pipe is designed to collect the exhaust gases from both manifolds using a Y-pipe. Vehicles with dual exhausts have a complete exhaust system coming from each of the manifolds that are sometimes connected via an H-Pipe. After the Y-pipe or H-pipe, exhaust gases pass through a catalytic converter that is designed to reduce exhaust emissions. From the converter the exhaust can pass through a series of exhaust pipes, flex pipes, resonators, and mufflers, before exiting through the tailpipe.

Catalytic Converters

The catalytic converter has a heat-resistant metal housing. A bed of catalyst-coated pellets or a catalyst-coated honeycomb grid is inside the housing. The converter contains small amounts of rhodium, palladium, and platinum. These elements act as catalsysts (entities that start a chemical reaction without becoming a part of the chemical reaction). As the exhaust gas passes through the catalsyst, oxides of nitrogen are chemically reduced (that is, nitrogen and oxygen are seperated) in the first section of the catalytic converter. In the second section of the catalytic converter, most of the hydrocarbons and carbon monoxide remaining in the exhaust gas are oxidized to form harmeless carbon dioxide and water vapor. An air-injection system or pulse air system is used on some engines to supply additional air that may be needed in the oxidation process. Catalytic converters have greatly reduced the output of harmful gases into the atmosphere and are an essential part of the vehicles emissions control system. So much in fact, that removing a functioning catalytic converter is against the law in many parts of the country. Be very sure of the situation and the laws in your state or province before removing or having your catalytic converter removed.

Caution: Performance Exhaust Systems

Performance exhaust systems are designed to increase the ability of these exhaust systems to flow a larger volume of air with less restrictions. A less restrictive exhaust system will generally result in more power up to the point at which there is enough back pressure to allow the vehicle to run properly. Back pressure is a measure of how restricting the exhaust system is to the used exhaust gases moving backwards in the exhaust pipes towards the engine. If an exhaust system does not provide enough back pressure, the engine may actually pull used exhaust gas in through the exhaust valve while it is still open during the beginning of the intake stroke. This would contaminate the fresh air-fuel mixture entering the combustion chamber and reduce the power generated by combustion. The point is, that there are limits to how large a performance exhaust system can be, before the "performance exhaust system" will actually start to rob horsepower (not to mention creating running problems).

Cutting Exhaust Pipes

Before you can install your new exhaust parts you need to remove the old ones. Occasionally, old exhaust pipes can be removed simply by unbolting the clamps and prying the two pipes apart. But if the pipes have been in place for any length of time, its much more likely that you will need to use a pipe cutter or a torch. Obviously the use of an oxygen/acetylene torch is beyond the scope of this article, so get yourself a quality exhaust pipe cutting tool. This tool is like a large set of plyers with a long chain that attaches to both jaws. The chain has a series of cutting wheels that dig into the steel when the chain is wrapped around the exhaust pipe, tightened, and rocked back and forth. Always cut the pipe towards the part you are replacing so the remaining parts will not be cut too short. This will leave you with a small portion that will need to be removed. Use a hammer and chisel to cut it away and remove it taking care not to damage the remaining pipes.

Fitting Exhaust Pipes

Fitting your exhaust pipes is usually fairly straight forward. You hang any exhaust components from their hangers and connect the pipes. However, there are a number of things to take into consideration when fitting your pipes, before they should be clamped down or welded together. The first is quite simply the alignment of the pipes. Check to be sure that each pipe is properly aligned and will not interfere with the suspension or touch any hoses, cables, or the floor of the car or hang down and touch the road. Also check that mufflers and tailpipes are not crooked. Also, pay attention to any embossed text on the muffler that may indicate which direction the muffler should be installed. Lastly, any exhaust pipes that fit inside and over one another should be done so that the pipe nearest the front of the vehicle fits inside the pipe nearest the rear of the vehicle. You may need to use an exhaust expander to expand the diameter of the rearwards pipe to fit, but be careful that you do not split the pipe.

Welding vs. Muffler Clamps

Most exhaust pipes can be clamped in place using special U-bolt-type clamps known as Muffler Clamps. These are often used by aftermarket repair shops because they are very cheap and very easy. You should be able to find these at your local auto parts store in a variety of sizes for a buck or two. Alternatively, you may decide to weld the new exhaust pipe in place once it has been fitted to the vehicle. Ideally, this would be done with an electronic welder such as a MIG welder. Unfortunately, they are expensive and often beyond the scope of the home do-it-yourselfer.