I'm using a cat replacement pipe now and I'm just wondering if on an s5 after the useless split air pipe is removed... should I cap it or just leave the port on the back of the engine open? I still have the ACV and air pump for the aux. ports. I couldn't feel any air coming out at idle or while revving, but maybe it only comes out in 5th gear or at certain loads?

 

Well if I recall correctly, the air pump was mainly for emissions purposes. I personally have your old S4 and the air pump was long gone when I got it, but it's not necessary to actuate the aux ports on an S4.. The split air pipe on an S4 has a small nipple that comes off it going to the port actuators that, with back pressure, opens them up.

Now on an S5 the ports are actuated with servos I *think*. It's been so long since I thought about it.

So I'm not sure if there is a check valve that trips a relay to open the aux ports at a certain psi on an S5 or if it is ALL indeed done by magic electrical gremlins that make the car move.

Hit up the search and look into it..

 

aux ports are all electronically activated by the ACV and air pump on an s5. There is a check valve, but I don't really see a purpose for it if it is only there to feed air to the cat which is now removed. As for now I just have the split air port on the engine un corked and no problems thus far. Just wondering if there is any good advice from the experts.

 

S5 aux ports and VDI are actuated by the ECU & 6PI and VDI solenoids directing air pressure to the actuators. They are not servos, they are nearly identical to the S4 counterparts, but use the air pump for pressure instead of exhaust gasses.

The check valve in the split air pipe is to prevent exhaust gasses from entering the ACV and air pump through that path. The port air path also has a check valve, which you can see if you remove the ACV.

You can go ahead and leave the nipple for the split air pipe uncorked, since the switching and relief solenoids (and their valves w/in the ACV) cut off the paths to the exhaust ports and split air pipe above 3500 RPM. There will be no pressure drop by having the nipple left open, so you're good.