This document discusses calculating back pressure and length in automotive exhaust piping systems. It provides the following key points: 1) The exhaust silencer should be located to allow for only a short tailpipe length to maximize noise reduction. 2) The maximum exhaust back pressure should not exceed 100 mbar to avoid increased fuel consumption and power loss. 3) The document provides examples of calculating additional exhaust length allowed while staying under the maximum back pressure using graphs and equations.

1. Back Pressure & Length
Calculation in Automotive
Exhaust Piping
Ahmadreza Aminian
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2. First Things First….
 The exhaust piping layout begins with silencer location which should be in
relation with tailpipe length. In order to obtain the best noise reduction,
there should only be a short tailpipe after the silencer as shown in the
graph:
 For all-speed engines, read the specified maximum speed for the engine
 For single-speed engines, read the operating speed of the engine
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3. Determining the longest length of
tailpipe (source: )
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4. Examples of long exhaust systems (i.e.
longer than 5 meters)
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5. Exhaust back pressure
 The back pressure in the exhaust system must not exceed the maximum
recommended exhaust back pressure, including silencers. A higher exhaust
back pressure leads to increased fuel consumption and a loss of power.
 The maximum recommended exhaust back pressure is 100 mbar for all
engines. exhaust back pressure in mmH2O. 1,000 mmH2O is equal to 100
mbar.
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6. Calculation example6

7. Graph for calculating additional length
in exhaust system
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8. Calculation process (source: )
 Backpressure is calculated by:
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9. Calculation process9

10. Calculation Process (Equivalent Length
of Straight Pipe)
 To obtain equivalent length of straight pipe for various elbows:
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