Ex-Eg-Driver

iTrader: (1)

I think this guy meant to say compression instead of BACK PRESSURE.

Roen

iTrader: (2)

a pumpless s5 n/a works with a backpressure pick up tube?

Did you try RB's S4 road race setup and compare it with a catted setup?

walken

iTrader: (6)

their new RR header has the 6pi pickup, but with the difference is chirping the tires into second gear with a cat. This is what changed my mind on straight piping an n/a.

Roen

iTrader: (2)

Interesting....

rotarygod

iTrader: (1)

It's a bit more complicated than saying they open with backpressure although that is what it is commonly referred to as. If you were to take air pressure readings with a manometer out the window of a car you could change the results based on which way the opening is facing. Typically when you test airflow with a manometer in an airstream such as radiator testing, you stick a small piece of foam over the end. Pressure maintains constant with ambient this way but there are no other outside forces actiing on it. If you held this tube out the window of a moving car you'd get the same amount of air pressure that you would if the car was stopped. However if you pointed the open end of the measuring tube into the wind, the air acting on it would change the apparent pressure reading on the gauge. This is because the momentum of air has force and this force is compressing the air inside the tube only which effects the gauge readings.

This is the same thing that happens with the "backpressure sensing tube". We are using air force not air pressure to open the actuators. However this air force is converted into pressure in the vacuum tubes to the actuators. If you look at the way the Racing Beat exhaust has the tube oriented, you'll notice that it points into the airstream. If they ran it straight in from the side and didn't point it forward, the actuators wouldn't open. Inside the cat there is a restriction and an increase in pressure which is never a good thing but this may be enough to open the actuators. You don't need backpressure to open them. You just need to use the leverage of air force to your advantage.

Having a cat may be "dyno proven" to increase low end torque but it is not due to an increase in backpressure. This is incorrectly interpreting the data at hand. An increase in low end power from an increase in "back pressure" is actually a more ideal exhaust velocity at the increase location. Back pressure is a useless term anyways as backpressure at one rpm isn't necessarily and probably not the same the same as at other rpms and no one ever states where they are measuring this.

Jeff Jones

the only back pressure you need is a turbo
now go fast damn it

SE7ENS_GARAGE

someones has been inhaling the exhaust fumes too much...(teh backpressure guy)