Greddy Type S Question

[Sparkys]

My RB25 has a Greddy plumb back BOV, with the normal inlet, outlet and line connection. However, it also has a second smaller line connection (see picture below, bottom left of the picture) which after reading around everyone suggests to leave it open.

My question is, if it can just be left open, what is the connection actually for?

[STATUS]

you can use it to control boost, much like a wastegate.

[Sparkys]

How so? A wastegate essentially bleeds off exhaust air to ensure constant turbine wheel speed which maintains a constant boost pressure. Are you saying that the Greddy BOV can somehow bleed off pressurised inlet air to only allow a certain amount of boost pressure into the plenum/motor etc?

If so, why do normal recirculation valves/BOV's not have the second nipple? Every other one I've seen just has a single nipple to receive pressurised air from the plenum or some such source. And if it is used for this, then shouldn't it be be blocked off normally? Otherwise it's just acting as an undesired boost leak.

Thank you,

Sam

[STATUS]

How so? A wastegate essentially bleeds off exhaust air to ensure constant turbine wheel speed which maintains a constant boost pressure. Are you saying that the Greddy BOV can somehow bleed off pressurised inlet air to only allow a certain amount of boost pressure into the plenum/motor etc?

If so, why do normal recirculation valves/BOV's not have the second nipple? Every other one I've seen just has a single nipple to receive pressurised air from the plenum or some such source. And if it is used for this, then shouldn't it be be blocked off normally? Otherwise it's just acting as an undesired boost leak.

Thank you,

Sam

Correct.

[Sparkys]

Thank you for your replies, however I'm not quite sure we're on the same page. I think what you're trying to describe is the basic function of a recirculation valve, to take the excess pressure away from the plenum/motor when the throttle is released, which I understand.

What I assumed from your first post was that the recirculation valve could be used as a boost controller (to increase or decrease boost) basically, and this concept I struggled with, but now I see that's not what you were suggesting. I understand that by modifying the spring tension I can decrease the boost slightly (as lower spring tension would allow boost pressure to return to the inlet tract earlier), but I see no way of increasing boost using a recirculation valve. I think we're on the same wavelength here now.

But unless I've misunderstood you, that still leaves my original question, what is the second nipple for? The two diagrams below are CAD drawings of a Greddy Type S which I lifted from another forum. The second picture suggests that the second nipple is used as a 'helper' to the springs and hence would need to be plumbed in to a pressurized line from the compressor. Does this sound right?

[geraus]

Hey there, I've had this BOV a while ago and i had it plumbed back and atmospheric, i got told the 2nd bottom hose is for boost to hold quicker when on/off the throttle. I remeber i had it connected to the plenum and the bottom nipple tapped of my greddy EBC.

[STATUS]

Thank you for your replies, however I'm not quite sure we're on the same page. I think what you're trying to describe is the basic function of a recirculation valve, to take the excess pressure away from the plenum/motor when the throttle is released, which I understand.

What I assumed from your first post was that the recirculation valve could be used as a boost controller (to increase or decrease boost) basically, and this concept I struggled with, but now I see that's not what you were suggesting. I understand that by modifying the spring tension I can decrease the boost slightly (as lower spring tension would allow boost pressure to return to the inlet tract earlier), but I see no way of increasing boost using a recirculation valve. I think we're on the same wavelength here now.

But unless I've misunderstood you, that still leaves my original question, what is the second nipple for? The two diagrams below are CAD drawings of a Greddy Type S which I lifted from another forum. The second picture suggests that the second nipple is used as a 'helper' to the springs and hence would need to be plumbed in to a pressurized line from the compressor. Does this sound right?

no you can use these bovs to control boost, we are on the same page. The second nipple is used to lift the valve @ the desired boost level.

Edited November 18, 2009 by URAS

[Savin]

I have the same bov...cant you just block it off??

[Savin]

block the 2nd nipple i mean...

[STATUS]

block the 2nd nipple i mean...

definatley not leave it open or else it wont open as a BOV. (its a vent when used in BOV operation)

Edited November 18, 2009 by URAS

[Savin]

Let me get this straight..

so i can tap the 2nd nipple on my boost controll ( i have a manual bc) by using a T piece??

Kinda confused on this one....Lame terms perhaps

cheers

[lachlanw]

plumb it to a pressure only sorce like greddy tells you to . its there to make the bov open fully . the same as a standard rb bov , being a diaphram type bov as opposed to a piston one. leave in to atmosphere and it will make the blow off valve sound louder as the valve will not open fully . plumb it up and it will open fully

[Savin]

yea i got that bit...atm it is plumb back...

What im getting confused is the second nipple....

Can i just use a T piece between the wastegate and mbc? or between the piping and mbc?

Im using stock piping way as i have cooling pro fmic...

[lachlanw]

http://www.mkiv.com/techarticles/hks_race_bov/hks_bov.jpg

[Sparkys]

no you can use these bovs to control boost, we are on the same page. The second nipple is used to lift the valve @ the desired boost level.

Ok, so then all I need to do is to have the second nipple plumbed in to a pressurised line at some point after the turbine but before the plenum. I can understand that and that fits in with all of my reading up on it. To be honest though, I struggle with the term "boost controller" being applied to a blow off valve, I suppose loosely the valve can 'control boost' by lifting the valve at a specific pressure, but it would only so this when off the throttle, otherwise the pressure from the top of the valve would just keep it closed. Thanks for your help, I'm only semi-confused now

[Beer Baron]

just listen to uras. leave it open. you don't need to hook it up to anything.

[Savin]

so its not compulsary to hook it to anything?

wouldnt it be leaking boost?

[l0WRB]

im running same bov and ive tighten it not to open anymore because the car feels sluggish coming onto boost 20psi

comes on alot harder with it not opening.. im wondering if i hook up the 2nd vacum line it mite hold it shut longer perhaps?

[Sparkys]

just listen to uras. leave it open. you don't need to hook it up to anything.

Yes I could do that, and I trust Trent and his knowledge. However, since I've built 99% of my car myself I like knowing for myself exactly what everything does so I can optimize the performance and efficiency of each part on it.

If you or Trent are willing to take the time to explain to me exactly how and what the second nipple does I'd really appreciate it. If not, that's fine, I'll try and look up as much information as I can on it.

Thanks if you can guys, but cool if you can't.

[Beer Baron]

when being used as a bov it vents air from under the diaphragm. my understanding (and I could be wrong) it just allows the bov to close again quicker. as trent said if you used it differently hooked a pressure source up to it you could use it as a boost control/pop-off valve. the pressure coming under the diaphragm would make it open at whatever boost level and vent boost out thus controlling boost.

my personal experience, I've only used a type S once, it was on a GTI-R, and that pipe was NOT hooked up to anything, and it worked perfectly fine.