I realize that some guys want a BOV that announces to everyone within earshot that they've got a supercharger. And it seems that all of the aftermarket BOV's are designed for that purpose.
To each his own, but personally, I prefer the stealth approach, and am looking for a BOV that gives off the least whistle sound on the upshifts or trailing throttle. And I realize that recirculating helps, but I want something that's really quiet to start with. Any suggestions?

 

Bosch Bypass Valve. Silent.

 

If recirculating many are quite but to a certain boost level.

 

Vortech Mondo

 

I've tried the Greddy Type-S, as well as a couple el-cheapo knock-offs of that design, even went to the trouble of taking apart and contouring the internal parts, but I still haven't been able to completely eliminate the whistle - even with recirculation (which doesn't really help the IAT).
Regarding the Bosch BOV that came standard with the Stillen SC kit, at what level of boost does that BOV become problematic? And how so??

 

I have a blitz BOV and I can BARELY hear it over the sound of the S/C. I definetly don't have any whistle

 

It's rated to hold 13psi max. Ptatohed is pushing 11 psi through it with no problems.

 

Bosch also makes a similar-looking but much higher performance BOV with the Part Number 0 280 142 110. Does anyone have experience with this one?

 

Agreed, my Blitz wasnt very loud at all, and when it did blow off it was a whooshing noise, no loud wistle or flutters.

 

My Vortech Mondo BOV isnt loud at all IMO. Sometimes I can't even hear it go off. It could also be due to my V1.

 

I have the Greddy type-s set up to recirculate on my turbo. People tell me it sounds like I'm torturing some little bird everytime I change gears. Sound/tone doesn't change regardless of boost pressure, sound just seems to last longer at higher boost pressures. However, when I really get on the shifting and make some fast shifts, it does seem to be a bit more of a fast "whoosh" sound. Not sure why.

I wonder how much placement has to do with sound? I think it's kind of like a flut or something, depending on where the opening is will determine the sound/note. I have my BOV mounted about 2-3" from the throttle body.

 

From my readings, it's supposedly best close to either end of the pipe from the SC to the TB (rather than in the middle). However, I believe that Greddy and some of the other makers of BOV's cater to the desires of the guys who like having a sound announce to everyone within earshot that they're blown. And while recirculation ought to help suppress the sound, it also tends to bump up the IAT. I'd prefer to avoid or eliminate the sound at the source (if that's possible).

 

Have you tried the Blitz BOV?

 

Sorry, but what is IAT? Intake Air Temp? Approximately how much does it increase the air temp?

 

One thing I'm finding in my experimentation, especially trying the Bosch BOV (and BTW, they also make a similar one with the last 3 digits of the PN being 110, made to be more durable and supposedly good for up to 30psi) is that during what would be closed loop operation you want the BOV to hold as much pressure as possible just short of having an adverse back-pressure-pulse effect on the supercharger, so that when you advance the accelerator (and not necessarily WOT) you have a good head of pressure quickly responding. What I found with even with that "better" Bosch BOV was that at partial throttle acceleration it was releasing some clear up almost to 5000 RPM (I put a whistle on to outlet hose so I could hear when air was passing).
With a hand-held vacuum pump I found that the stock Bosch BOV (as supplied by Stillen) opened at about 6" hg, while the "better" Bosch opened closer to 10" hg. For those of you who have and monitor a vacuum/boost gauge, you know that most of your everyday driving is with the vacuum above 10" hg. On the other hand, the Greddy which I've been using (with it's own unwanted whistle when backing off on the throttle) is adjusted to open at 18" hg and has noticably snappier throttle response. Now if that "better" Bosch only had a stronger spring inside of it I'd be all set.

 

Yes, IAT is Intake Air Temp, and how much will depend upon individual setups.

 

/\ Interesting stuff there Curt. Thanks for sharing. Having a whistle mounted to the BOV must have made a ton of noise! Served its purpose though.