I know that they work based off of backpressure, but thats where it ends.
There is a tube coming out of the main cat that goes to what?
Does the backpressure go through something else, then open them, or are they directly connected?
IE: How much emissions stuff can be taken off before have to go to solenoids or wired open/left closed.
If anyone has insight to a better write up on how it works or something that would be great. Looking at the FSM and Haynes repair manual are just confusing me on how it actually works.

 

The tube from the main cat (split air pipe) goes up into the engine bay and has a larger opening that looks kind of like a mushroom. This is where the ACV then connects to. A little ways down from that back towards the CAT is a little nipple on the split air pipe. The actuators connect to that via a vac line to get the backpressure for opening the ports.

What a lot of people do that have s4's when they remove emissions is to remove everythign (including the CAT) except the airpump and then hook the aux ports up to the airpump for actuation. The racing beat pre-silencer also allows you to still activate via the split air pipe because it has a tube just like the main CAT. So you have some options based on your plans.

 

*kicks idea in*


Any S4 exhaust that has a pressure tube for auxilary port activation will ALSO work on S5's for Aux port systems and VDI system. All you need to do is make a line from the pressure tube to the various pressure input nipples/noid(VDI) and it should work blingorrificaly.

 

So if I get the racing beat presilencer that has the split air pipe for back pressure...
I can cap the ACV and just have that pressure opening the ports directly?

 

I don't exactly know what happens to the ACV at that point. But you will still be able to hook up the split air pipe to the silecner to actuate the aux ports.