GReddy Type S BOV Install Question

realfinn · Post by **realfinn** » Fri Aug 25, 2006 3:36 am

So I finally decided on the GReddy over the HKS. Got the GReddy Type S today and noticed that there are two nipples for valve control. I assume that the large nipple on the top would plum directly to the Intake like the old BOV. The bottom nipple however I'm not sure. The only thing I can come up with is that it is for faster shutting of the BOV. So does that nipple run to the turbo outlet (only place I can think to find a pressure source) or should I just cap it off and not use it?

I know there is probably going to be someone that says that I shouldn't use the BOV because of the MAF/Richness problem. But I am going to experiment with a few easy/cheap ideas I have to make the problem better or go away.

free5ty1e · Post by **free5ty1e** » Fri Aug 25, 2006 3:22 pm

IIRC, Vikash said the lower nipple should be connected to the turbo outlet for the Type S. I haven't had a chance to try this set-up yet, but that does sound like the solution I remember for the leakage at idle after a blow-off.

realfinn · Post by **realfinn** » Fri Aug 25, 2006 4:47 pm

So basically I would T off right before my MBC? Will this degrade the performance of the boost controller?

free5ty1e · Post by **free5ty1e** » Fri Aug 25, 2006 5:17 pm

Yep, that's how I understood it. It should not have any effect on your boost control unless you create a leak somewhere in the process - that connects to the other side of a diaphragm (I believe) in the blowoff valve that reacts to the pressure.

realfinn · Post by **realfinn** » Fri Aug 25, 2006 7:05 pm

Thanks!

free5ty1e · Post by **free5ty1e** » Fri Aug 25, 2006 7:09 pm

Ain't no thang

napphappy · Post by **napphappy** » Sat Aug 26, 2006 2:17 am

the only prob I see is that lower nipple may leak boost(maybe affect your MBC). It does(leak boost) on my Type-S.

free5ty1e · Post by **free5ty1e** » Sat Aug 26, 2006 3:19 am

That's probably not good, I'd have thought that would be a sealed section of the Type S. I've never seen internal diagrams however. Wonder if vrg3 knows the answer. V?

realfinn · Post by **realfinn** » Sat Aug 26, 2006 2:55 pm

Haven't installed it yet. But I did notice that I can blow right through the lower nipple. If I cover the outlet with my hand I can feel the pressure. I did a little work with it this morning. Decided to take it apart....I can't help myself when I don't understand something. I was going to post some pictures of the thing disassembled but I can't get the image hosting to work (won't let me set a password). But I did find this site that someone spent a little time on.

http://www.stealth316.com/2-greddy-bov-anatomy.htm

Pretty cool model. Pretty close to what I saw.

When I had mine apart I noticed that there is no seal between the lower nipple and the outlet. Just metal against metal in the valve guide area. So I assume that the leak was intended and not just a manufaturing defect.

realfinn · Post by **realfinn** » Sat Aug 26, 2006 3:12 pm

So I was doing some thinking. If the chamber that the lower nipple went in to didn't leak at all then you would basically have a small compression chamber in there and the pressure would reach whatever you have your boost controller set to. Since the pressure would have no wheres to go during operation it would just be throwing the pressure back down into the turbo outlet. I think this would pretty much defeat the purpose of the BOV all together. Sound right? We need V power! Where's the V-button?

free5ty1e · Post by **free5ty1e** » Sat Aug 26, 2006 5:00 pm

The diagram pretty much backs up what we were thinking before though, it says that boost helps push the plate up from the lower nipple -- and looks like it's supposed to be a separate volume of air to me. I don't have my Type S handy to mess with or take apart, but it sure wouldn't make sense to design that lower nipple chamber to take boost to help open and close the BOV and then not seal it.

Hmm.

Adam West · Post by **Adam West** » Mon Aug 28, 2006 5:35 am

Awesome link! Thanks for posting that!! Nothing expert to add to this Q tho. I'll shut up now and keep reading. Cheers, Adam

napphappy · Post by **napphappy** » Mon Aug 28, 2006 5:49 am

Yeah, thats why I havent installed mine. I dont really want a boost leak.
I thought about modding it so that I could put a valve seal around the stem but havent got around to it.

vrg3 · Post by **vrg3** » Tue Sep 05, 2006 3:25 pm

Hey dudes.

I'll try to find time to come back and discuss this more, but in the meantime:

If you install the valve between the intercooler and the throttle, and connect that nipple to the compressor outlet, boost won't exactly "leak" through the nipple and around the valve stem. It'll just be bypassing the intercooler. But the amount of air is miniscule in any case.

And here's an email I wrote to Phil a long time ago when we were trying to figure out how the valve worked:

From: Vikash
To: Phillip
Date: May 10, 2005 4:03 PM
Subject: My guess

The diaphragm is pushed downward by a spring. The tension on this
spring is controlled by the adjustment nut at the top of the BOV.

The valve opens when the diaphragm moves upwards. This happens when
the vacuum at the upper nipple (normally connected to the intake
manifold) is enough to overcome both spring tension and whatever
pressure is present at the lower nipple (connected either to the
atmosphere or to the compressor outlet). So the valve's position is
determined by the differential pressure between the two nipples.

(Technically, the pressure at the inlet of the valve is also involved
since it pushes up against the spring too, but let's assume GReddy
designed it so that effect would be minimized by giving the diaphragm
a lot more surface area than whatever the seal is at the valve seat.
This seems reasonable since it would explain the hat-shaped top of the
BOV.)

So. If you leave the lower nipple disconnected, you end up in a
situation where manifold vacuum alone determines when the valve opens.
To keep the valve closed at idle, you have to set the spring so it
won't allow the valve to open until you get to around 10 psi of
vacuum. This is pretty extreme; it's easy to get compressor surge with
less vacuum than that. So you can either set the spring to shut the
valve at idle, or set it to prevent compressor surge. But probably not
both.

But if you connect the lower nipple to a pre-throttle boost pressure
source, then you can set it up so opening requires both high vacuum in
the manifold and high pressure at the compressor outlet. So say you
set the spring to, say, 11 psi. Manifold vacuum at idle will never be
that high. But, if the turbo's making even the slightest amount of
boost, it'll push over the limit and let the valve open. And if the
turbo's making more boost, the valve will open with even less vacuum.
So you have a good chance of setting things up to minimize or
eliminate compressor surge while also minimizing or eliminating leak
at idle. You still end up with a little more lag since you're not
equalizing pressures across the compressor wheel, but that effect is
pretty small anyway.

OEM valves also work this way -- they operate on the differential
pressure between the valve inlet and the intake manifold. It just so
happens that the valve inlet is also a source of boost pressure. But,
GReddy's design has a bonus (aside from the obvious adjustability). It
allows you more flexibility in positioning the valve.

If you put an OEM valve in the pipe going from the compressor to the
intercooler, you have to deal with the pressure drop across the
intercooler; this can make the valve "leak" when it shouldn't. That's
why the WRX valve is positioned very well at the intercooler outlet.
With this GReddy valve, you could install it on the intercooler inlet
pipe if you want (and that way maybe avoid heat soaking the
intercooler with recirculated compressed air), but still get the
proper opening pressures by just adding a fitting at the intercooler
outlet (or throttle inlet) for a tiny vacuum hose. With this
adjustable valve, you could try to compensate for the pressure drop
across the intercooler by increasing spring tension, but then you run
into the problem that the pressure drop is dependent on the actual
flow rate, which varies. That's not to say you can't make it work
(many people, you and I included, are using the compressor outlet as a
BOV boost reference), but it's suboptimal.

Cliff's notes:

* I think everyone not using the lower nipple is doing it wrong and is
either consuming dirty air or not protecting their turbo.
* I think that ideally you'd connect that lower nipple to something between the
intercooler and throttle, but, failing that, connecting it to the compressor
outlet would likely be workable.
* I think the way you'd adjust the valve would be to disconnect the
lower nipple, tighten the nut all the way, run the engine at idle,
loosen the nut until the engine stumbles, and then tighten it back
down slightly.

Does that make any sense?

-Vikash

free5ty1e · Post by **free5ty1e** » Tue Sep 05, 2006 5:25 pm

Thanks V that's what I was looking for! I actually remembered correctly, giggity giggity!

My Type S is destined for my '91, when I get around to working out a front-mount for it. Eventually. I hate that word, but unfortunately the majority of my projects are under that status at the moment. Dag nabbit.

realfinn · Post by **realfinn** » Tue Sep 05, 2006 6:00 pm

Thanks V. BOV Sounds great!!

dzx · Post by **dzx** » Tue Sep 12, 2006 9:27 pm

I've got the top nipple of mine connected to the intake manifold and the lower nipple goes to the intake side of the turbo.

legacycentral bbs

A forum for 89-94 BC-BF(BJ) Legacy Owners and Fans

GReddy Type S BOV Install Question

GReddy Type S BOV Install Question