legacycentral bbs

So ive noticed when i rev my motor it will produce a rattling/clicking sound like something is shaking/fluttering. Ive issolated it down to my bypass valve. It will rev up maybe 500-750rpm and click/rattle in sync with my #4 cylinder (where the vac line comes off) for a few seconds and then goes away with higher rpms. Now ive also been experiencing the same sound when i get under WOT and it seems to preform poorly. If i let off and hit it again i can get it to go away. My boost gauge (T-ed off this line) shows a smooth sweep from vac to boost.

How much pressure would it take to damage this unit? Should i replace it with another one or should i try and use a newer wrx BPV? Its a 93 ss with a TD04 and WRX TMIC running at ~8-10psi post IC.

IIRC, the stock BPV can handle ~15-16 PSIg before leaking... but I don't think it gets damaged by the pressure even then.

It shouldn't be able to make any rattling / clicking sounds either - that's strange. The only sounds it should be able to make are hissing (leaking) or a Darth Vader-like exhale noise between shifts (if your recirc hose is off)

Are you sure those sounds are coming from the BPV? Not the valvetrain?

Yeah it makes the whooosh sound when im shifting and it does still function properly. Ive applied a vac on the small line and it allows air to pass through the large one. When the vac is removed it doesnt allow air through the large line

The function of this valve is open durring presence of vac and closed with pos pressure correct? So any time im not under boost it will be open right?

Im 200% sure its coming from the valve as when i rev the throttle plate i can isolate my BPV and feel it vibrate in my hand as it coencides with the sound.

ive confirmed its the valve by removing and plugging the vac line to the valve and reving it. it doesnt produce the sound/vibration at all. is there any way to use a stock wrx bpv or will it interfere with my throttle/cruise cables?

The valve will open when there is a pressure differential between the intake manifold and the intake charge pipe, so only when the throttle plate closes with pressure in the piping.

It won't close all the way afterwards though, so yeah it will leak a bit at idle.

That's still really forking wierd that the BPV could be making those sounds. I think it's just a diaphragm and a spring - I don't see how that's possible. I'm interested to hear what others on the board think about this.

You do have it hooked up to the intake manifold don't you? It won't work properly without that reference, I know that.

Edit: Not sure about the WRX valve, I think if you want to change the stock BPV out you will pretty much have to customize some piping, which is why this is usually never done without installing an intercooler of some sort. Get a WRX top-mount IC and you can use the BOV that comes with it pretty easily... but then again I'd always recommend the extra effort required to go front-mount anyway.

free5ty1e wrote:Get a WRX top-mount IC and you can use the BOV that comes with it pretty easily...

Its a 93 ss with a TD04 and WRX TMIC running at ~8-10psi post IC.
My concern is the throttle bodys are different between a wrx and my car that the intercooler is made for. Ive heard of issues with it hitting the throttle and cruise connectors off the butterfly making it not possible in our legacys. Any thoughts? I might just get one off the local subaru forum cheap and try it out.

Yes it is still running off the vac nipple on #4, right below the brake booster vac line. Having my boost gauge t-ed off this line shouldnt affect the BPV correct?

Huh.... you got me, sure sounds like everything should be coo. Anyone else have a clue here?