ASE P2 Test Prep: Exhaust Parts

ASE P2 Test Prep: Exhaust Parts

Information to help parts professonals pass the ASE P2 test.

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 two to three times as much as galvanized or aluminumized steel. Inside a muffler are perforated tubes, baffles and chambers that control noise. Some mufflers are also packed with a fiberglass material 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 they may have a straight-through design to reduce backpressure for improved power and fuel economy. Many also increase the noise level of the exhaust.

For more information on catalytic converters, please refer to the section on Emission Control parts on page 46 of the ASE Test Primer feature.

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 prebent 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. 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 nonasbestos, 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 also used for muffler/resonator connections. 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 are rubber straps and grommets used to support the exhaust system. They need to be replaced if broken or missing, or if the exhaust system is being modified.

A "hot" product with younger drivers today are large chrome or stainless steel exhaust tips. They are for looks primarily, but some are designed to replace a rear muffler or resonator to reduce backpressure.

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