1g-gte...put on a plumb back BOV, its sucking air in...is this normal??

[LUXPWR]

Hey all , sorry if this is a totaly stupid question. Anyway I got a Drift plumb back BOV from Autobarn on the weekend, as I hated the gay loudness of the turbosmart megasonic one the car came with. After putting the new BOV on and starting the car i put my hand on the outlet and noticed that it was sucking air in. Should this be happening?

Car seems to be running ok. I havent run a line from the BOV back to the air intake yet, i just capped it off with a little mini air filter thing. Just not sure if this sucking should be happening. The way i think of it, shouldnt vacuum seal the valve? Am i just being punished for buying a cheap ($160) BOV???

[thechuckster]

doesn't sound right at all. With no vacuum line to the intake manifold it will act like a relief valve at boost (boost pressure only has to over come the spring) but otherwise it should be sealed shut.

[MWP]

Its perfectly ok for a recirc BOV to do that (mine does it too).
As long as you have plumbed it back to between the turbo and AFM its all good.

If it wasnt an recirc, or if you plumbed it to between the air-filter and AFM you would have problems.

If it worries you though, just increase the piston spring pressure in the BOV.

[thechuckster]

weird - none of my fuly-spastik BoVs have leaked on vacuum (well, not leaked in a way that I could hear/feel/notice). Even the bottom-shelf turbosmart jobs have sealed.

[TheDarkRaver]

What do you mean when you say "I havent run a line from the BOV back to the air intake yet" are you talking about the small hose which is normally located on the top of the BOV?

the BOV shouldnt be sucking in air. The vacuum should pull the BOV shut. I would take it back you Autobahn as it sounds like you have a faulty BOV.

[LUXPWR]

Thanks for the input fellas. The vacuum line from the inlet manifold (that goes into the top of the BOV) is connected.

I dont have a line from the outlet of the BOV back to the inlet yet, i havnet got any large diameter hose atm. If i put my hand on the outlet, there is quite a bit of suction, and the revs drop a bit on the engine. Winding the spring in all the way does not change this.

Also, if i pinch the vacuum line shut the revs drop on the engine, the same as if i put my hand on the BOV outlet. Not sure if that info is useful.

MWP - why cant i run the return line between the air filter and turbo inlet? I have read online this is how it should be done? However i have no experience and and no idea really so im open to suggestion/wisdom.

Here's a pic of how its setup atm. Comments/suggestions?

[thechuckster]

The vacuum should pull the BOV shut.

it - well, a turbosmart BoV for example - does the opposite - when you have boost in the intake manifold it assists the spring in keeping the BoV shut. When you have manifold vacuum (e.g. throttle is shut) it pulls the pistons backwards (against the spring) allowing air to go around the valve.

(it's actually a combination of the pressurized air in the inlet-side piping and the vacuum behind the valve which results in the piston being pulled back against the spring and allowing air to escape the BoV).


edit: 'If i put my hand on the outlet ... if i pinch the vacuum line shut the revs drop on the engine' - that's a significant leak?

[NME308]

CODSWOLLOP guys...

The basic action a BOV is to OPEN under vacuum when the throttle blade/s are slammed shut to vent excess pressure. It will depend on the particular application and valve as to whether it will 'hang' open at idle. Mine hangs open at idle and blows air - I chose one which would. I have positive pressure in the intake tract even at idle and need to ditch it due to being blow through carb. If your turbo has bugger all back pressure then at idle certain BOV's may well suck in air!

Cheers,
Jason

[MWP]

It will depend on the particular application and valve as to whether it will 'hang' open at idle.

No... it depends on the strength of the spring in the BOV.
A BOV with a weak spring will open up at idle, no matter what engine its on.

I have positive pressure in the intake tract even at idle...

Not possible
(oh, unless your engine is supercharged)

[MWP]

MWP - why cant i run the return line between the air filter and turbo inlet? I have read online this is how it should be done? However i have no experience and and no idea really so im open to suggestion/wisdom.

You have this correct??
AIR FILTER ---> AFM ---> TURBO

If you connect the BOV to between the air-filter and afm, youll be taking unmetered air into the engine (ie, itll run rich or lean depending on the situation = bad).
It needs to be connected in between the afm and turbo to work correctly.

If your engine is MAP sensored (has no AFM), you can plumb it back to where ever you like.

[LUXPWR]

MWP - pretty sure i have no AFM, i have an aftermarket single turbo and am running an EMS computer. There is nothing 'electrical' in front of the turbo inlet.

So back to the initial question - is the BOV a dud?

Chuckster - you say that pinching the vac line or covering the BOV outlet and getting a drop in revs is a sign of boost leak? Wouldnt it be likely that the leak is in the BOV as its sucking air in, or perhaps internally as it also happens when the vac line is pinched?

[MWP]

Ah ok, yup you have no AFM and are MAP sensed then.
It can be plumbed back to anywhere between the turbo and air-filter.

I very much doubt its a dud... they cant fail easily.
Stick your finger in the turbo side of the BOV and push on the piston.
If it moves ok, odds are the BOV is ok.

Plumb it up and itll be fine.

[NME308]

No... it depends on the strength of the spring in the BOV.
A BOV with a weak spring will open up at idle, no matter what engine its on.

You are correct in a limited understanding of the principle. While putting a light enough spring in any BOV will allow it to hang open at idle, not all BOV's actually have the correct valve/surface areas to function properly i.e. some will not seal under boost if adjusted to open at idle. For my HQ a custom pair of rather large BOV's were machined up with enough surface area to allow them to open at idle and also clamp shut properly under boost. These are atmo venting units and at idle they hang open and blow air out.

Not possible
(oh, unless your engine is supercharged)

So mr roll your eyes... If you care to read my build thread you will clearly see it is turbocharged. At idle - yes I did mention it is turbocharged - the turbo is creating a stiff breeze which introduces a positive pressure into the crossover pipe necessitating me to have a BOV which will hang open at idle due to my blow through carb setup. Now as above mentioned not all BOV's can function properly when set to hang open at idle so I selected mine specifically for the job.

Cheers,
Jason