Can anyone explain why some ports read vac or just boost or both? curious y and they they are mostly in the same spot.
also does anyone have a diagram of which vac port reads what on the throttlebody? thanx!

 

Here u go this should be what your looking for

 

yea kinda thanx. i guess its for a s5? my s4 has 3 and 3

 

Ports that always read vacuum even when the car is under boost would be like the nipple in the turbo inlet duct that pulls crank case and evaporative emmisions. It has an entry perpendicular to flow to create a vacuum and it never sees turbo boost.

A nipple that only sees boost would be one where the entry is inline with the airflow and after the turbo like the throttle body nipple that feeds boost to the top of the fuel injector air bleeds and the oil injector tops to normalize their flow.

A nipple that sees vacuum and boost would be like all the other nipples on throttle body and manifolds that are after the turbo and have and entry perpendicular to flow which creates vacuum that the turbo then overcomes with boost.

 

o ok i see. thanx for clearning that up.

 

Sorry did not know what u had i thought S5 but if u got to FAQ and manuals u can find out and u can also DL all the manuals so if u ever have a Q u might beable to A it befor u ask.

 

actually i apologize its for a s4 i didnt see the twin scroll there. i guess some s4 came wih 4 nipples in the back instead of 3.
thanx

 

That diagram up above is Fucked up.

 

Yes it is messed up, I posted that a while ago as a tentative plan vac routing. That setup didn't let the boost gauge work, I moved the hose to nipple 1 since I didn't need the twin scroll since I upgraded to the BNR turbo.

I was in the process of removing emissions, the diagram was a visual aid in this thread which ends up looking different by the end. There's also an explanation of which nipples show boost/vac in my thread below-

'87 TII Throttle Body Vacuum Nipple Question - Just Double Checking - Please Verify

 

so u "T" the bov and the boost sensor to the same spot on the pass side of the uim?

I figured running the bov to one of the front ports...

the boost sensor goes to the pass side of the uim
and the boost gauge to the bottom on the back of the uim

 

yeah thats how I have it set up now, is this not okay?

 

some people argu to leave the map sensor with its own vac source and t something else.
i had mine t'ed with bov and boost gauge and left map sensor alone. i used map sensor or the side of UIM and the bov/boost gauge on i think the bottom front vac port on manifold

 

I just figured u would want them each on their own besides the bov atleast on my setup will be as close to the tb as I can get it.. I don't want to run the vac line all the way to the other side of the intake

 

I have heard these before, and it makes sense to me, though so far I haven't seen any problem from using the same vac source for the BOV and Pressure sensor. And I'm one that likes to put the BOV right by the turbo so it's a convenient as well.

 

OK I am going to update this the best I can and get some things figured out (or try to)

I have my boost sensor by itself on the pass side below the bac valve
I have my fuel pressure regulator on the inside of the lim ont he sideways nipple


For the 3 nipples on the front of the S4 throttle body
I have the top 2 capped off
the bottom one going to the top port on my BOV (bottom nipple on bov capped)

For the back of the TB (4 ports)

I currently have them all capped off
my boost gauge will go on the lower most nipple in the rear

this is how my car is setup, I have no twin scroll, no vac spider, no bac valve, egr etc.

NJGreenBudd IME it is best to have the BOV closest to the TB as possible the reason why is because you want all of the back pressure in the charge pipes to be expelled BEFORE it can get to the compressor (causing compressor surge).

 

It wasn't that bad a diagram. I read the thread on a *off* day and vented my spleen a bit. Sorry 'bout that.