just found thison pistonheads,gassing section
Ok then. Try this.
The exhaust valve opens. High pressure exhaust gas blasts its way down the exhaust header; a pressure gauge plumbed into the header measures 10 psi.
A fraction of a second later and we're into overlap; both valves are now open.
Pressure developed by the supercharger/turbo whatever measures 7 psi as it goes into the cylinder.
10-7= 3psi of pressure(BOOST level with 10 psi backpressure).
We remove the restricted exhaust system and plumb in a mythical zero backpressure exhaust( demon tweeks or halfrauds special ) and now we get the following.
Pressure measured in the exhaust reads zero, the same 10 psi boost pressure as before is also present at the intake.
Guess what? 10-0= ? 10 psi boost getting INSIDE the cylinder, thats 7psi more than the previous exhaust.
Now if you still doubt the validity of the statement, do the following practical experiment to convince yourself.
Take a hosepipe, attach it to a pressure gauge on a "tee" and with a means to shut off its flow at the nozzle end.
Then take a 25litre drum, turn the tap full on with the tap at the nozzle fully OPEN and read off the pressure while timing how long it takes to fill the 25 litre drum.
Once complete, chuck the water away and write down the figure you got for the pressure and the time.
Then do it again with the tap closed off (restricted) to say halfway (experiment may be required) then check the pressure and see how long it takes again to fill the 25 litre drum.
I will tell you the result. The first scenario will have a LOW pressure registered and a LOT of flow, resulting in a fast time to fill the drum.
The second scenario will give a HIGH pressure (backpressure) and will take much longer to fill.
This is exactly the situation faced by an engine when operating.
Ie; Only so much time to fill/empty the cylinder ( the 25 litre drum) with only a certain amount of pressure available to get the job done.
Any restriction in the exhaust will hinder the engines capability to exduce its spent gasses, and is seen as a pressure rise in the pipe.
Backpressure is bad bad and bad again and is an unwanted effect on any engine.
Regards deltaf.
Ok then. Try this.
The exhaust valve opens. High pressure exhaust gas blasts its way down the exhaust header; a pressure gauge plumbed into the header measures 10 psi.
A fraction of a second later and we're into overlap; both valves are now open.
Pressure developed by the supercharger/turbo whatever measures 7 psi as it goes into the cylinder.
10-7= 3psi of pressure(BOOST level with 10 psi backpressure).
We remove the restricted exhaust system and plumb in a mythical zero backpressure exhaust( demon tweeks or halfrauds special ) and now we get the following.
Pressure measured in the exhaust reads zero, the same 10 psi boost pressure as before is also present at the intake.
Guess what? 10-0= ? 10 psi boost getting INSIDE the cylinder, thats 7psi more than the previous exhaust.
Now if you still doubt the validity of the statement, do the following practical experiment to convince yourself.
Take a hosepipe, attach it to a pressure gauge on a "tee" and with a means to shut off its flow at the nozzle end.
Then take a 25litre drum, turn the tap full on with the tap at the nozzle fully OPEN and read off the pressure while timing how long it takes to fill the 25 litre drum.
Once complete, chuck the water away and write down the figure you got for the pressure and the time.
Then do it again with the tap closed off (restricted) to say halfway (experiment may be required) then check the pressure and see how long it takes again to fill the 25 litre drum.
I will tell you the result. The first scenario will have a LOW pressure registered and a LOT of flow, resulting in a fast time to fill the drum.
The second scenario will give a HIGH pressure (backpressure) and will take much longer to fill.
This is exactly the situation faced by an engine when operating.
Ie; Only so much time to fill/empty the cylinder ( the 25 litre drum) with only a certain amount of pressure available to get the job done.
Any restriction in the exhaust will hinder the engines capability to exduce its spent gasses, and is seen as a pressure rise in the pipe.
Backpressure is bad bad and bad again and is an unwanted effect on any engine.
Regards deltaf.
