Back pressure calculation process in exhaust systems with example

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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