I've done some searching and found alot of speculation but no real concrete answers.

I have a bit of a franken engine. It's 6-port irons, with turbo rotors, swapped into an FB.

It has a FMIC and stock s4 turbo. s5 NA intake.

I have a big TIAL BOV (I didn't build the car so I'm not positive to model, but it is not a knockoff) plumbed after the IC right before the throttle bodies. It is the type of valve that has ports around the circumference and a piston inside that moves fore and aft. My vacuum source is in the UIM immediately above where it connects to the LIM.

My issue is this, while doing something else under the hood, I noticed the BOV is open at idle, just wide open. If I rev it in neutral, it kind of flutters open and shut.

Actually driving under load, while I obviously can't see it, it builds positive boost, no leaks, and crisply snaps open when the throttle is closed. It works well enough that i didn't think there was an issue with it. The car has dyno'd at 244whp with a stock turbo at 10psi, so obviously something is working.

However, the car does have a rough idle and a tendency to stumble upon returning to idle. I had attributed this to a half-assed tune (e6x) and a big street port, but could this be causing it? is this behavior normal?

A friend had suggested a diaphragm problem or maybe trying to draw vacuum higher in the intake, right behind the TB. I just wanted a 2nd opinion.

 

There is a hex screw on the top of the tial BOV.... adjust it (tighter) so that the spring pressure overcomes the pressure the turbo creates at idle....

Your plumbing is 100% correct. The vacuum the car produces at idle is what is holding it open.....

 

hmmm, the tial BOV does not have a hex screw on top. Well not mine atleast.

I also thought the BOV was open at idles and close when on the gas? The reopens when you let off the gas.

 

Vacum is what opens it. you idle under vacum.

 

Isn't it vacuum before TB + positive intake pressure that opens it? With 244 and a stocker?

 

No. It's impossible to have vacuum before the throttle body.

As stated, vacuum opens it, pressure closes it. Jump off the throttle, create vacuum, open valve, vent pressure between compressor and throttle body.

I know the valve in this particular case. It has the lightest Tial spring in it and it does open at idle.

 

You need to adjust the spring, add shims, or get a heavier spring. Its NOT supposed to be open at idle. Engine vacuum isn't whats supposed to open the valve solely. Its a combination of vacuum after the throttle body butterflies and pressure in your pipes that vents it. The spring is supposed to be tight enough so that it is CLOSED at idle with ambient pressure in the intake pipes. If its open at idle, your sucking in UNFILTERED AIR into your engine.

There are BOV's designed however to remain open at idle. These usually have a small filter on them. The theory for this is better off boost throttle response and quicker spool-up because the engine is allowed to breath easier. Its not sucking through all the piping, intercooler and turbo. But that's NOT the type of BOV you have. The Blitz and Turbonetics BOV's come to mind (they can be had with air filters on them)

BTW, I recall this being discussed several times on this forum, specifically people using the Tial units. Tial makes a heavier spring to cure this, give them a call.

~Mike...........

 

My TiAl is open at idle. Always has been. However, at idle my turbo seems to be pushing more air than is consumed and is constantly bleeding air. Hopefully that is keeping my contamination to a minimum. It does have the lightest spring available though. TiAl started using the lighter spring specifically for rotaries in order to fight compressor surge, as we built less vacuum than piston engines.

FYI, the oem bov opens at ~ 4 inHg, so it is always open at idle as well. (Though it comes connected to the air cleaner..)

..dave

 

http://www.tialmedia.com/documents/w3_tial_bov50_sp.pdf

 

i had to order a stronger spring for my 20B...it is pulling alottttt of vacuum

 

stock s4 turbo. 6 port irons ported pretty heavily i'm told (didn't do it myself).
big fmic, 3in exhaust all the way back.

s5 n/a intake with aux ports open/vdi disabled. tuned via haltech e6x by ludwig. It's rich as hell but makes stupid power for a stock turbo.


As for the spring, I pull 17-18" at idle, so I ordered a stronger spring. I'll update this when i get it in.

 

engine side of TB is going to be negative boost (vacuum) so your line for your BOV coming from your Mid intake manifold sucking on the BOV..yes it will open. as soon as enough +boost is made to where there is no longer any vacuum in the intake will close the BOV...you are running a front mount you can try to making it to where the BOv is closed at idle but you will notice poor throttle response because the motor is trying to suck air through the turbo and all the plumbing of the intercooler..but if you leave the BOV open at idle then you bipass the turbo and plumbing and suck air righ there at the BOV therefore making better throttle response

 

oh only thing is you might want to put a filter on the BOV if you are going to run it open..

 

Nice summery of my post , or are you comprehending what I just said and was thinking aloud and let your fingers follow your thoughts? Except your implying that all BOV's are supposed to function in this manner (open at idle) when they are NOT supposed to function this way. They should have enough spring tension to keep the BOV CLOSED AT IDLE. Again, unless it was designed to function with it open at idle (very few that are designed to operate in this manner).

~Mike...............

 

alright, i am a little confused here, should a bov be open at idle or not?
its shouldnt matter what bov or what your setup is should it?
pretty sure the stocker is open at idle on the fd(if my memory is correct)

 

no its not suppose to be open at idle......... i had this same issue with my tial bov just get a stronger spring. make sure you dont go overboard with a super stiff spring just get one rated to what psi your spooling at

 

incorrect, I've been doing some research http://www.frozenboost.com/stpg.php?page_id=bov

it should be closed at idle, and you select it based off of engine vacuum. Boost has almost 0 consideration in the BOV spring

 

Correct, wastegate springs=psi, bov springs=idle vacuum

 

I bought a BOV spring rated for 18-22 in. vac, perhaps it's a bit stiff. My car pull 16-18 in at idle.

I noticed the BOV doesn't sound crisp like a whip anymore, it's more fluttery. I'm debating buying a softer spring, but is it possible to cut it to make it shorter? My tial does not adjust and the next step down is for 13-17in which I was afraid was too soft.

In other news, my old s4 turbo took a shat. If my spring is too stiff, and it was surging, could it have killed it in ~1000 miles? the turbo was old and on its way out, I'm just afraid of this spring with another turbo. it does open after letting off under load, but as I said it's not a crisp clean crack like with the light spring.

 

somebody? can I trim my BOV spring, or is that too ghetto?

 

Yes, you can. I had to do it on my POS Turbo XS RFL and it worked great.