Internal Combustion Engine basics, mainly airflow vs TQ&HP
12-02-2005, 09:02 PM
#21
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The reduced diameter of an exhaust after the collector is a wave tuning thing,lenght and diameter of the pipe after the collector changes the flow rate at given rpm and exhaust port/valve size is another factor you should consider while making diameter changes for each motor and RPM
12-03-2005, 06:06 PM
#23
Originally Posted by Ari G
The reduced diameter of an exhaust after the collector is a wave tuning thing,lenght and diameter of the pipe after the collector changes the flow rate at given rpm and exhaust port/valve size is another factor you should consider while making diameter changes for each motor and RPM
Take care, Ed
12-06-2005, 01:26 PM
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The reason why you don't want your exhaust too big is mass. A wider (or longer) exhaust holds more air. You have to push the air in your exhaust out the tailpipe before the gas in the engine can get through.
You don't want your exhaust to narrow, because narrower pipe represent more restriction to flow, which results in higher pressure, which results in less of your exhaust gas leaving your cylinder, which results in lower VE, which results in less power. That is why the diamater of your tubes has a happy medium, and slapping on an 8" coffe can exhaust is a bad idea.
Some exhausts decrease in diameter toward the tailpipe because of temperature. Hot gas takes up more space. Gas coming out of your engine is VERY hot, so it requires wide pipes. As you move toward your tailpipe, the gas is cooling all the way, so the optimal pipe width decreases.
Tuning has to do with pipe lengths, temperature, cylinder pressure, back pressure, etc. Certain conditions could result in less power by removing back pressure, because that effects tuning (this is assuming that your car was very well tuned to begin with). Removing all back pressure, then retuning your car would be best.
You don't want your exhaust to narrow, because narrower pipe represent more restriction to flow, which results in higher pressure, which results in less of your exhaust gas leaving your cylinder, which results in lower VE, which results in less power. That is why the diamater of your tubes has a happy medium, and slapping on an 8" coffe can exhaust is a bad idea.
Some exhausts decrease in diameter toward the tailpipe because of temperature. Hot gas takes up more space. Gas coming out of your engine is VERY hot, so it requires wide pipes. As you move toward your tailpipe, the gas is cooling all the way, so the optimal pipe width decreases.
Tuning has to do with pipe lengths, temperature, cylinder pressure, back pressure, etc. Certain conditions could result in less power by removing back pressure, because that effects tuning (this is assuming that your car was very well tuned to begin with). Removing all back pressure, then retuning your car would be best.
12-06-2005, 03:28 PM
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the gas is cooling all the way, so the optimal pipe width decreases
Certain conditions could result in less power by removing back pressure, because that effects tuning (this is assuming that your car was very well tuned to begin with).
during an exhaust stroke lowers power.
At what point in time are you wanting backpressure to be present?
Last edited by Adrenaline_Z; 12-06-2005 at 03:42 PM.
12-07-2005, 07:35 AM
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Originally Posted by Adrenaline_Z
Not really true. Want to explain the theory behind stepped headers?
Not a chance. Having a high pressure in the exhaust system (at the port)
during an exhaust stroke lowers power.
At what point in time are you wanting backpressure to be present?
Not a chance. Having a high pressure in the exhaust system (at the port)
during an exhaust stroke lowers power.
At what point in time are you wanting backpressure to be present?
12-07-2005, 12:47 PM
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No offense to you, or anyone else, but I have a real tough time with that word (backpressure).
If you can relate backpressure to high pressure, then we're better off.
Even then, you can never eliminate high pressure events from the exhaust system.
High pressure will exist, and is a result of pressure waves bouncing around,
mixing, etc.
It seems when people speak about "Backpressure", they feel it is an absolute
amount/value and can be eliminated totally and exhaust gasses are free to pass through.
If you can relate backpressure to high pressure, then we're better off.
Even then, you can never eliminate high pressure events from the exhaust system.
High pressure will exist, and is a result of pressure waves bouncing around,
mixing, etc.
It seems when people speak about "Backpressure", they feel it is an absolute
amount/value and can be eliminated totally and exhaust gasses are free to pass through.
12-08-2005, 07:27 AM
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Originally Posted by MadBill
Contrary to popular belief, pressure does not affect the speed of sound in a gas, only temperature does (and mixing with other gases, e.g. water vapor, carbon dioxide, etc...)
http://en.wikipedia.org/wiki/Speed_of_sound
My bad, so then there are no cases no matter how unlikely when having high pressure in your pipes is a good thing.
