I'm almost done swapping out my S4 intake for a nice clean S5 one I had sitting around and I'm also done rebuilding my throttle body so everything is getting a bit closer to sparkling.

I've run into a couple of little things that I ahve to sort out though.

First off is sourcing the air for the BAC valve. I have some nice chrome pipe sitting here from eBay and would like to hack it up and run my filter down in the wheel well but don't want to make a mess of the stock tube and hack it up to retain the big nipple for the BAC.

I came across one of these little dudes in my pile of parts and thought this might work but don't know if it's going to cause problems because the BAC would be pulling air in that the AFM doesn't know about. That's where I got stuck on the whole "should I hack up the stock pipe or not" area. Here's a pic of how I'd like to do it (with a bit of a shorter hose of course . )



Second question is related to this little guy:



That piece normally sits under the BAC valve and is also connected to the bypass air pipe. From what I understand it provides extra air when you have the A/C on. I no longer have an A/C system so I could care less about it and it's one less thing to have sitting around in there. Is there any other function it serves?

Last and final question. Does anyone know how many PSI that little split air pipe puts out from exhaust back pressure? I've had no problems with it opening up my aux. ports correctly but I'd like to know if the ACV will pop open if I leave it T-eed off like it is in the first picture. I can always adjust when it opens by using a little brass ball valve if enough pressure exists.

If in it's stock form there isn't enough pressure, can I block the main split air pipe off where it hits the intake (facing towards the firewall) to decrease the volume it fills, hopefully creating enough pressure? I don't have an ACV or airpump anymore so that pipe is not required for anything other then activating my aux. ports.

Thanks for any advice guys! I'm hoping I can finish putting all this stuff together and maybe get it running tomarrow evening and test out the whole thing and see how many little things I missed.

 

No to the first picture. Ditch it to the second. I'd say like 4-5psi, depending on what you've got in the tube.

 

Ok, BAC will be fed off the normal line, thanks.

I'm running the Racing Beat header/pre-silencer combo and it's been much better about opening the aux. ports so I'm hoping it'll work out with the ACV. I can't do the grease trick with the ACV to see if it opens like the aux. ports.

 

I just finised putting the TB on and started 'er up. Aside from a little whistle by the UIM>Dynamic chamber joint it ran pretty well. It does have a lumpy idle and would randomly start doing the surge idle, but I adjusted the TPS and secondary plates and it smoothed out a bit.

I'll finish tuning tomarrow and will probably break something and come up with a question again.

I didn't take it on the road since I haven't given everything the once over again but it does seem to rev more freely then with the S4 intake. We'll see tomarrow.

 

Swap over the VDI also?

Using a switch?

 

If you're not going to operate the 6PI and VDI systems using an air pump, solenoids and rpm switches, you shouldn't even bother putting the S5 intake on. Exhaust backpressure alone is a hopeless method to use on a modded car, and it can't be used to operate both the 6PI and VDI since they need to open at different revs. If you don't open them both at the right time, most of the gains will be lost and the whole exercise will be pointless.

 

After you get it running, try this test:
Run a hose from the VDI to inside the cabin.
Hook up a mity-vac hand pump output so you can manually pump open the VDI.
Cruize along at 5K RPM in 2nd.
Pump open the VDI & HANG ON!

You will be re-thinking the value of an RPM switched pressure source to the VDI.

 

The second picture is only the part of the cold start assist. It is only used to put extra air into the system when starting (supplimenting the BAC).

You could do something like this for the BAC feed:

if you are wanting to keep the same line.

and I agree with the above posts, no sense even doing the VDI intake unless you are using a RPM switch and solenoid to run it.

 

With that first pic, that will not work. The source for the BAC must come from a point that is part of the intake that is after the AFM. Allowing 'unmetered' air to enter the system when the bac turns on is gonna make your car run like ***. Thats why the stock system draws air from the throttle body elbow duct that attaches the afm.

 

That's exactly what I ended up doing.

I'm going to go out and grab an air pump and RPM switch today and just wire that up instead. The aux. ports can be left alone since mine are opening correctly.