How to verify BOV is working properly?

hobieboy · 10-26-2006, 01:26 AM

Hi,
I have one of the GSF BOV that vents to atmosphere (I'm running EFI).

I'd like to understand how do I know it is working properly in the sense that -
a) It is venting sufficiently,
b) It is venting at the right time.

I really don't like the sound but I can hear that it opens even when I lift from cruise speed (i.e. from no boost to close throttle). Is this normal / desirable?

The unit is said to be adjustable. But how to determine what to adjust it to?

thanks.

greglepore · 10-26-2006, 03:19 AM

http://www.gofastbits.com.au/index.php?parentid=tech_info&option=tech_info

Good discussion of BOV's.

hobieboy · 10-26-2006, 05:10 AM

Thanks for the link Greg.

It confirmed my thinking of how BOV works and seems to say that the fluttering sound I hear, particularly loud at cruise->close throttle situation, is an indication that mine is set too tigghtly.

I'll try to loosen it a bit & see if it changes anything then.

Any idea about how to set the BOV spring properly?

greglepore · 10-26-2006, 06:02 AM

No, sorry. My experience has been with non adjusable bov's where you have a fixed spring that matches the wastegate-but I believe that you want the bov setting and the wastegate setting to match. When the valve opens, it makes a "phssss" sound, loud and brief, not a flutter.

RickM · RickM's Garage

Quote:

Originally posted by greglepore
No, sorry. My experience has been with non adjusable bov's where you have a fixed spring that matches the wastegate-but I believe that you want the bov setting and the wastegate setting to match. When the valve opens, it makes a "phssss" sound, loud and brief, not a flutter.

Halfway down the first page of this thread Tsuter describes in detail the operation of a BOV. There is no matching of BOV to Wastegate.

Turbo guys - Question about BOV's.

fierochris · 10-26-2006, 03:57 PM

its not good if you can hear it when its not under load. that means its leaking boost before it enters the intake. your spring is too loose not too tight. it shouldnt be venting till you shift, or let of the throttle.

BTW, venting into the atomispher does not give you any performance gains. just the neat sound. and a little insurance

930turbo · 930turbo's Garage

I agree, the spring tension is too loose. This allows the valve to open under light manifold vacuum. Another symptom of low spring tension is, after a hard charge and when the throttle is initially closed, the boost/power drops off abruptly and can actually upset the balance of the car if your cornering. Be careful.

hobieboy · 10-26-2006, 04:13 PM

I hear it only when I shift or lift (ie closed throttle).

I thought its normal as there is pressure differential (very low under throttle plate & "atmospheric" above) when I lift. According to the the GoFastBit site, the sound means the air is venting back to the turbo - so bad.

Did I mis understand?

hobieboy · 10-26-2006, 04:17 PM

Quote:

Originally posted by 930turbo
I agree, the spring tension is too loose. This allows the valve to open under light manifold vacuum. Another symptom of low spring tension is, after a hard charge and when the throttle is initially closed, the boost/power drops off abruptly and can actually upset the balance of the car if your cornering. Be careful.

That seems exactly what I'm experiencing - when I lift/slow down my acceleration even @ 4000 RPM, my boost would instantly disappear pretty much completely.

Guess I need to increase tension on the BOV spring then?

I'm confused

greglepore · 10-26-2006, 05:39 PM

Any time the pressure differential exceeds the spring pressure, it opens-it shouldn't open on a slight lift where the car is still "on the throttle" but feathered, but should open instantly on a full lift .

The only time the valve should open is a rapid throttle close under boost; if its opening under low/no boost throttle closure, then its not tight enough.

hobieboy · 10-26-2006, 06:04 PM

To be sure, this is my situation:
I'll hear a loud fluttering sound (assume its BOV opens) when:

a) I lift off throttle (for upshift or simply let off the gas pedal) from any speed including say cruising at 40mph
b) If I accelerate (say for on ramp) then have a momentary hessitation in pressing the gas pedal, my boost will instantly disappear

Based on these, I think the BOV is too loose?