● MUFFLERS AND RESONATORS — Used to control exhaust noise, the muffler or resonator is mounted behind the catalytic converter. A second muffler or resonator may be located further back for additional sound control. Vehicles with dual exhausts usually have separate mufflers for each side, but some may share a common muffler.
Mufflers and resonators may be made of galvanized, aluminumized or stainless steel. Stainless is the most durable material but also costs much more than galvanized or aluminumized steel. Inside a muffler are perforated tubes, baffles and chambers that control noise. Some mufflers also are packed with a fiberglass material (roving) to provide additional noise absorption.
Mufflers most often fail from the inside out due to corrosion caused by the acids and moisture in the exhaust gases. Mufflers mounted behind the rear axle typically have shorter lives than those mounted closer to the converter because they run cooler and collect more moisture. Some mufflers have small drain holes that allow moisture to escape.
Replacement mufflers come in various types. Direct fit replacement mufflers look and install the same as the OEM muffler. Universal mufflers fit a wider variety of applications and may require adapters to install. Performance mufflers use fewer baffles and restrictions, or have a straight through design and/or flow straighteners to reduce backpressure for improved power and fuel economy. The trade-off may be increased exhaust noise, which some customers want.
● CATALYTIC CONVERTER — See the section on Emission Controls.
● EXHAUST PIPES — Include the head pipe that connects the exhaust manifold to the converter, the y-pipe that connects the right and left sides of a V6 or V8 engine into a single exhaust, the exhaust pipe, which connects the converter with the muffler, and the tailpipe which usually extends aft of the muffler or resonator. Some FWD cars have a flexible head pipe to accommodate engine vibrations. These can be very expensive to replace.
Pipes come in different diameters and materials. Many OEM systems are stainless steel to improve durability, but most aftermarket replacement pipes (except for some performance exhaust systems) are plain steel to reduce replacement costs. Pipes are pre-bent to fit specific vehicle applications.
Special exhaust tools may be needed when replacing pipes or mufflers. These include pipe cutters and pipe chisels for separating corroded pipes and connectors, and expanders for repairing or installing new pipes and mufflers.
● EXHAUST MANIFOLDS — Carry hot exhaust gases away from the engine. Bolted to the cylinder head(s), the exhaust manifold(s) connect to the head pipe or Y-pipe. Most are cast iron, but some are welded stainless steel tubing. Some exhaust manifolds also include “pre-cat” converters to reduce cold-start emissions. Cast iron manifolds can sometimes crack, causing a loud exhaust leak. Aftermarket replacement manifolds are available for most engines. So too are performance exhaust headers that have a separate tube for each cylinder. Most are four-into-one headers that improve exhaust flow for better fuel economy and performance. Street legal headers must have the required emission hookups and fittings for the O2 sensor and EGR valve. New exhaust manifold gaskets should always be installed with new manifolds or headers.
● GASKETS — Help seal connections to prevent exhaust leaks. The gasket between the exhaust manifold and cylinder head is subjected to extreme temperatures and may develop a leak. These gaskets may be non-asbestos, graphite or metal. High-temperature RTV silicone can also be used to seal the exhaust manifold or headers. Donut gaskets may be used between the manifold and head pipe, and flat gaskets may be used at other pipe connections in the system (typically import applications). New gaskets should always be installed when pipes are replaced.
● CLAMPS — Hold the pipes together, and are used for muffler/resonator connections, too. New clamps are always needed when replacing mufflers or pipes. Clamps come in different sizes and must match the diameter of the pipes or connectors.
● HANGARS — Rubber straps and grommets used to support the exhaust system. Need to be replaced if broken or missing, or if the exhaust system is being modified.
● HEAT SHIELDS — May be used around exhaust pipes to reflect heat away from the passenger compartment, fuel lines, brake lines or fuel tank. The shields may come loose can cause rattles, or fail from corrosion. Heat shields should be replaced if damaged, corroded or missing.