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View Full Version : Back pressure?? we dont need no stinkin back pressure..


Pedro_The_Swift
1st May 2020, 07:58 PM
Get your thinking caps on!!


https://www.youtube.com/watch?v=E8sm0c_kSh8
Slunnie
1st May 2020, 09:49 PM
I thought I was the only one on the planet that thought needing exhaust back pressure was a load of bull****.

Except on 2-strokes, but thats a far more complex scenario.
Blknight.aus
2nd May 2020, 06:24 AM
I thought I was the only one on the planet that thought needing exhaust back pressure was a load of bull****.

Except on 2-strokes, but thats a far more complex scenario.

and on some NA configurations where you're using the back pressure to do some freaky stuff with pressure pulses and exhaust velocities at the ports in the manifold to increase scavenging at a given RPM band... kind of like 2 strokes but ass about.
Slunnie
2nd May 2020, 11:43 AM
and on some NA configurations where you're using the back pressure to do some freaky stuff with pressure pulses and exhaust velocities at the ports in the manifold to increase scavenging at a given RPM band... kind of like 2 strokes but ass about.

Thats it, the pulses are not the same as back pressure, its all about extraction, where 2S are about reflected pulses refilling the CC with charge that blows through.
Blknight.aus
2nd May 2020, 05:57 PM
Thats it, the pulses are not the same as back pressure, its all about extraction, where 2S are about reflected pulses refilling the CC with charge that blows through.

however you do need some back pressure for the pulses to work. to make the pulses work in the manifold you need (and this is the really simple version) some back pressure which changes with the flow velocity. if you have no back pressure you dont get to set up the flow which makes the pulses work.If you're going for a total 0 back pressure configuration you might as well just run pipes as fat as you can as short as straight as you can from the ports
Slunnie
2nd May 2020, 06:35 PM
however you do need some back pressure for the pulses to work. to make the pulses work in the manifold you need (and this is the really simple version) some back pressure which changes with the flow velocity. if you have no back pressure you dont get to set up the flow which makes the pulses work.If you're going for a total 0 back pressure configuration you might as well just run pipes as fat as you can as short as straight as you can from the ports

They do, if they can.


Here is a better explanation of whats happening.


https://youtu.be/jjPeP_Nn2B4