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Exhaust System 444-544

posted by  jmenacker on  Wed Mar 5 03:52 CST 2003
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last visit: Wed Jan 21 09:31 CST 2009
[RELATED]

Phil:

Thanks for the excellent information on exhaust pipe sizing. However, I don't quite understand the advantage of using a smaller pipe under _any_ circumstances. Any comments on the fallacy of the following reasoning would be appreciated:

At any given engine speed and load a fixed volume of gas must be displaced from the engine cylinder. It is true that a given volume of gas will have greater velocity in a smaller pipe. However, the rate of flow will be the same in a larger pipe as a smaller pipe with the exception of friction losses.

There will be a greater resistance to flow as velocity is increased. The gas travelling along the walls of the pipe experiences a certain amount of friction based on the roughness of the wall. Changes in direction also contribute to resistance to flow.

The higher velocity in a smaller pipe might somehow be beneficial for creating negative pressure on the discharge side exhaust valve when the valve is closed. What am I missing here?

Thanks much for all the help you provide.

Joe Menacker






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