BOV for dummy
 

1990 1.6, small turbo, saab ic, over the top pipes, Bipes timing controll and running 5 PSI so far. I have a BOV from ebay which sits just before the TB and has a line for the top of the diaphram and one for the bottom. I have the spring adjusted down now so it does not draw air at idle nor does it blow off. I run the wastegate control from the intake manifold. BOV is VTA. I have trouble deciding how to hook up the lines.
- If I put the top of the diaphram to intake this will allow the BOV to open at idle correct cause it is seeing about 19 vac correct? lousy idle etc.
- if I put the the bottom of the diaphram to boost will this not open the BOV under boost since it is push the valve and also pushing the diaphram so I loose boost?

I am a confused please help

Kenny

most BOVs are open at idle. there is more vacuum pull the diaphragm up, to overcome the spring pressure.

when you tighten the spring to seal at idle, it's too much pressure for the boost to overcome when the throttle is closed.

as for plumbing: top port should go after TB, bottom port should remain open or attach pre-intercooler at the turbo.

this is on your car with MS correct? there should be no idle issues with the valve completely wide open.

Ok I was unsuccessful getting my older version MS to work so I have reverted to the original AFM and Bipes. If the BOV is open at idle she dies as this is unmetered air.

So since you have the AFM and stock ECU you are going to need to recirculate that BOV. That's the only way or else get to work on that megasquirt.

^what he said, your best bet is to buy a cheap reliable oem bov off a sabb or something of the likes which has provisions to be recirculated to a location pre afm. this is how oem vehicles are plumbed and it works fantastic, you wont have the ricer bov sound though if thats a concern.

Would you not recirculate to post AFM, pre turbo? If you are pre AFM it would be the same as being open correct?

post AFM pre turbo. air has been metered, you dont want to meter it again.

Thanks very much we will work it out!

shouldn't it be closed?

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

Engine Vacuum Reading / Color Use Spring
Between:
- 22 and -23 in/Hg Pink -12 Psi (-24 in/Hg )
-18 and -21 in/Hg Un-painted -11 Psi (-22 in/Hg )
- 14 and -17 in/Hg White -9 Psi (-18 in/Hg )
-10 and -13 in/Hg Black -7 Psi (-14 in/Hg )

I could be confused

yes almost any bov will sit closed. reason it opens is because when u let off the throttle the tb shuts boost still in the pipe but vacuum in the manifold so ur reference will have vacuum but the pipe will be under pressure, vacuum on top boost on bottom pushes the spring up. but it dosnt matter, if he has a stock maf he will benefit from recirculating the bov. if it stays open during idle the spring is too soft. if it dosnt open after boosting your spring is too stiff. sounds like you have a spring from a supercharged car tbh, a centrifigul blower uses same bov as any old turbo car but with a very light spring in it which allows the boost made at idle or partial throttle to escape.

Last night I fabricated a recirculate system using the same BOV. Kind of ghetto but I though I would try it. Very good results. I backed off the spring and ran the top line to the intake mani and the bottom line to turbo. Recirculated air enters back after the MAF just prior to the turbo. Idles perfectly and is silent. I had a strange noise from the turbo before this that almost sounded like it was rubbing but with the recirc it is quiet. The sound always came when the tb was closed or closing. I suspect now it was the pressure build up because the tb closed quickly. Now I have to retighten my exh manifold as it seems to leak under boost and whistles. Thanks for the input!

If you set up most push type BOVs to be closed at idle, the spring will be too heavy to open under boost and you'll surge and flutter.