Exhaust system: Components and design

Here you will find valuable and useful workshop tips about the design and function of an exhaust system.

The primary task of the exhaust system is conducting the combustion gases of the engine past the driver's cab into the open air. Noise caused by combustion is reduced to the permissible volume by integrated mufflers. For exhaust gas purification, catalytic converters or particulate filters are also installed in modern motor vehicles with internal combustion engines.

Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their work. The information provided on this website is intended for use by suitably qualified personnel only.


Design of an exhaust system: Basics

Essentially, an exhaust system consists of exhaust manifold, Y pipe, catalytic converter, particulate filter, pre-muffler, middle muffler, rear muffler and the corresponding connecting pipes. Depending on the vehicle type and engine concept, the individual components can be combined in different ways. The vehicle manufacturer adapts the design of the exhaust system, the positioning and dimensioning of the components to the relevant vehicle. This optimally adapts the flow resistance and noise level on the vehicle. Due to the sound-absorbing properties of the particulate filter, the pre-muffler can be partially dispensed with in diesel engines.


All components of a motor vehicle’s exhaust system are coordinated with each other. Modification or installation of unauthorised spare parts will result in the loss of the vehicle's operating licence.

Task and function of an exhaust system: Functionality


The actual exhaust noise is produced by the pulsating exhaust gas flow from the individual cylinders. Reflection and absorption can be used to dampen the sound energy in the exhaust system. The mufflers take over this task and reduce the noise generated by the combustion engine while regulating the exhaust gas back pressure to optimise engine performance.


In the muffler, obstacles are deliberately placed in the way of the exhaust gas flow to reflect the sound waves and prevent further proliferation. These can be implemented using cross-section changes, pipe deflections or chambers. As a result, the sound waves are deflected and are partially cancelled by superposition.


With absorption, the exhaust gas flow passes unhindered through one or more chambers in the muffler. The chambers contain a perforated pipe and porous material such as stone wool or glass fibre. The sound waves pass through the holes into the filling material, which absorbs the higher frequencies.


Since both types of sound damping are suitable for different frequencies, they can also be combined in one muffler.


In addition to combustion noise, the exhaust system also generates noise due to vibrations and natural frequencies that are transmitted to the vehicle body via the fastening elements. These can be specifically reduced through the positioning and design of the components or by using elastic suspensions or additional vibration dampers.

Noise level

According to EU regulation, the current permissible noise level limit for new vehicle types from 1 July 2016 is set at 72 to 75 dB(A) depending on the vehicle class.


From 1 July 2024, this value for motor vehicles will be reduced to between 68 and 72 dB(A).

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