Turbo guys - Question about BOV's.

[WydRyd]

What high HP BOV do you guys recommend for re-circ application? (i.e: allows you to re-circulate charge air back into the intake for silent operation)?

I'm considering this GREDDY Type R unit.

[pjv911]

Im curios too. Do you need a aftermarket BOV when boost is at 1bar ?
Ive heard that Forge makes an excellent unit. Any other inputs ?

Kurt Williams

[WydRyd]

Kurt, my car is aftermarket turbo'd, so it never had a BOV. For big HP application, a higher flowing BOV is typically recommended to vent reverse pressure pulses before they reach the compressor and cause surging.

I guess the BigHP Supra guys run these Greddy units successfully, so I may just make the jump and get the TypeR. I like the fact that you can recirc air back into the intake for a more stealth application. It has a 2" outlet

[WydRyd]

These Billet Aluminium BOV's are only $65 on EBay and are a drop in replacement for the 996TT's, so I'm just wondering if it'd be suitable for a single turbo application running only 1.0-1.3bar max?

[rsrfan]

I run a billet forge unit on my 930. Unlike the stock unit, the forge valve contains a piston, oring, and spring whereas the stocker uses a diaphram. The Forge unit may be disassembled and serviced via allen bolts on the top of the valve http://www.stratmosphere.com/forge_valves.htm

The unit in your picture does not appear to allow for such servicing. ( this may or may not be necessary, however, if nonserviceable you may be forced to purchase another unit if it fails)

JP

[tsuter]

Blow Off Valves(BOV) blow off air. Diverter Valves (DV) recirculate air. Two different animals for a similar application.

Whichever you use, the main thing is get one with a PISTON. Caps added for emphasis. Tial BOV or Forge or Bailey DV. Want to see a cheapy??? Shove your finger in a 930 stock DV. Scary. Can you spell leaker???

Or course next we'll have peeps say they were designed to leak at idle.....

[mb911]

tial is among the best. My only gripe is it vents to atomosphere so you have to listen to it but they work wonderful and very nicely made

[Craig 930 RS]

We need a 930 Forum on Pelican.....!

[tsuter]

Ben, You can barely hear the Tial BOV. Comparatively it is very quite. I have to listen for mine to open.

Here is a pic. The Tial BOV is obvious....it cannot recirculate.
No comments on my welding skills please.....



Now, here is one you can hear all the way around the block. Great for attracting attention in your turbocharged Supra.



And lastly the stock plastic 930 DV. Still in its box on my shop. Guess why its not in use.....

[mb911]

Thad I just hear mine do the chatter some times it makes me think rice and I don't like that. I have the same one as you

[tsuter]

Here is a snap of the Bailey Diverter valve installed in my 1.8T. That's a manual boost controller in front of it.

For your app, I might consider a DV over a BOV since it seems you anticipate EFI in the future. Maybe two DVs

[tsuter]

Originally posted by mb911
Thad I just hear mine do the chatter some times it makes me think rice and I don't like that. I have the same one as you

That's strange. I get no chatter. Just a nice "hiss" on transitions. Chtter makes me wonder if yours is opening and closing rapidly when it should not. "Searching" if you will. The spring choice will make a difference.

[RickM]

Does the BOV spring typically match the Wastegate? IF not how is the BOV pressure calculated?

[tsuter]

Originally posted by RickM
Does the BOV spring typically match the Wastegate? IF not how is the BOV pressure calculated?

No...no direct relationship at all.

The BOV opens on differential pressure across the throttle plate.

Example...throttle plate is open...you got anything from vacuum to 20+psi in the manifold based on the turbo, wastegate, boost controller etc. The pressure or vacuum is the same on both sides of the throttle plate so the BOV/DV stays nicely closed as it should with its spring.

Now you lift off throttle to shift. Throttle plate closes momentarily and you have vacuum below it (3-5-10psi) and maybe some level of boost (3-5-10psi) above it. What ever that differential sum is and if its greater than the BOV/DV spring, it opens.

My BOV spring is 11psi but the boost controller is set at 8psi.

Don't relate the two directly. All it takes is boost+ vacuum across the throttle plate greater than 11psi and the BOV will do its thing.

A low spring weight BOV is bad as it may cause the BOV/DV to flutter at idle when the TP is basically closed but you have vacuum below greater than the spring weight.

Spring weight too high and it doesn't open when maybe it should and you lose some turbo speed on gear shift transition.

Clear as mud??

[beepbeep]

Originally posted by tsuter

And lastly the stock plastic 930 DV. Still in its box on my shop. Guess why its not in use.....

First:
Thing on the picture is not the 930 BOV. 930 didn't have plastic BOV's. They have gigantic cast-aluminium rebuildable BOV with interchangable gaskets. 930 BOV looks like this:



Second: thing on picture looks like 964 Turbo BOV. It works perfectly fine as well. And yes, it is designed to leak slightly at idle. As soon as pressure builds up it tightens. Unfortunately, ricers don't get this and keep trying to run them as open-air BOV's and end up with vacuum leak.

Third: All you buying bling-bling BOV's believing you actually improve something, check this picture:

[tobluforu]

So true about the bling, bling, honk, honk, hiss, hiss or whatever, but saabs use the same type of plastic diverter valves. I run about 19 psi on my viggen and the damn stock plastic valve that you see in this pic. above blew it's top right off at 14 psi (limp home mode). So the expensive ones are great in the sense that they will last forever, are cleanable and some are adjustable. If it was me I would spend a tad more money and get one.

[tsuter]

OK here is the Porsche p/n for the nice plastic DV 993 110 337 50

And I knew some peeps would say it's designed to leak at idle......

It's like WODs vs FODs for you enginerds.... "Works as Designed" vs "Failure of Design".....

That's only one reason its still on the shelf...

[RickM]

Originally posted by tsuter

Clear as mud??

Actually a very good explanation, thanks.

My 50mm Tial has the 11# spring and I was planning on a similar (to your) WG spring.

Sounds as if one could determine if the BOV is in the sweet spot by ear.

[youngkang]

How about this?

[WydRyd]

I was planning to use TWO of those billet aluminium units I depicted above. One before the IC and one just after the IC. Two for extra flow. I'm only planning to run 1.1-1.3bar max, so I think they'll suffice. The TiAL is nice, but too loud. I have one on at the moment and I hate it!