BOV adjustment???

ej22t · Post by **ej22t** » Mon Feb 03, 2003 9:53 pm

Hi everyone, I would like to install an aftermarket BOV by HKS, and I would like to know do I have to do the adjustment on the BOV or just direct bold-on?

Does anyone has install an aftermarket BOV? Please help!

Ben

Imprezive · Post by **Imprezive** » Tue Mar 07, 2006 2:50 am

Work on your grammar. You will have to adjust it depending on how much boost you are running.

Hey I have a 91 turbo with an ej20g in it!

vrg3 · Post by **vrg3** » Tue Mar 07, 2006 3:35 am

Imprezive - Easy, there; Ben's first langauge isn't English.

Ben - Yeah, you'll have to do some adjustment, and even then it's not clear that you'll get it to always work right... Phil (BAC5.2) was using an HKS SSQV for a while and if I remember correctly he always seemed to either have compressor surge problems or leakage at idle. He did better with a Greddy Type S blowoff valve.

free5ty1e · Post by **free5ty1e** » Tue Mar 07, 2006 3:03 pm

I found the opposite; I had a GReddy Type S and it was a pain to adjust (idle leakage and what not).

Got an HKS SSQV; no idle leakage, no adjustments, guaranteed to hold any pressure up to something ridiculous like 60 PSI. Unfortunately, it's whistle is LOUD and I haven't figured out how to remove it yet - and there's no way to run this valve in a recirculating setup.

The HKS is great; minor compressor surge at transatmospheric shifts but nowhere else. (I'm not even sure if this is avoidable at all) The GReddy caused all kinds of compressor surge depending on where it was adjusted.

vrg3 · Post by **vrg3** » Tue Mar 07, 2006 3:40 pm

Did you hook the Type S up correctly, Chris? With one reference line at the compressor outlet and one at the manifold?

BAC5.2 · Post by **BAC5.2** » Tue Mar 07, 2006 6:00 pm

Yea, there are 2 reference lines. Most leave one (the compressor outlet one) open, and that's the problem. Vikash and I spent a bit of time fine-tuning everything on my BOV, but we got it really great, and I didn't have any problems. It wasn't really that loud, just nice and smooth. Opened quickly, closed quickly, it was nice.

My Type S was great. The HKS was annoying after a while.

Now, I no longer have the Type S, and I now have a TurboXS Type-H. Haven't used it yet, but I'll probably recirc it, and I doubt I'll have any problems.

free5ty1e · Post by **free5ty1e** » Wed Mar 08, 2006 1:28 am

I had run mine with the second reference open; I'll have to check it again when I've got a shop, I prefer it's sound to the HKS.

napphappy · Post by **napphappy** » Wed Mar 08, 2006 7:53 am

Can somebody explain exactly how the Type S is supposed to be plumbed, Im putting one on soon.

vrg3 · Post by **vrg3** » Wed Mar 08, 2006 4:12 pm

This is from an email I wrote to Phil way back when we were trying to figure it out while looking at some diagrams of the valve on the web:

Me, in an email to Phil wrote: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?

napphappy · Post by **napphappy** » Wed Mar 08, 2006 8:42 pm

Cool thanks.
do You mean inHG instead of psi when talking about vaccum?

vrg3 · Post by **vrg3** » Wed Mar 08, 2006 8:55 pm

BAC5.2 · Post by **BAC5.2** » Thu Mar 09, 2006 1:41 am

I believe we verified the TypeS correct setup in a way back NASIOC post and another DSM post.

I'm gonna miss that BOV. It was cool.

napphappy · Post by **napphappy** » Thu Mar 09, 2006 2:38 am

vrg3 wrote:No.

So PSIa, Just ckecking

vrg3 · Post by **vrg3** » Thu Mar 09, 2006 3:02 am

No, not absolute...

Sorry for being a little clumsy with the units... By "10 psi of vacuum" I mean "10 psi less than atmospheric pressure." That is, roughly 5 psia at sea level, or roughly -20 inHg gauge.

napphappy · Post by **napphappy** » Thu Mar 09, 2006 3:34 am

Thanks for clearing that up, Im now slightly less confused

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BOV adjustment???

BOV adjustment???