BOV Open at idle?

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MTBSully

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Just noticed while my car was idling that my Tial Q 50mm BOV was open. Isn't it supposed to be closed at idle? I did some research and got some mixed opinions. Seems to me that if it is open at idle that would cause a bit of a vacuum leak? Our cars pull around 19" at idle which means I should have the Unpainted tial spring. I took the BOV apart and it looks like I have the Black spring which is designed for motors that produce 8-11"

Should be as simple as swaping out the spring for a stiffer one correct?
 

MTBSully

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MTBSully

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Just an FYI for people in the future, just got this ermail from Tial:


Ian Kautzman <[email protected]>
2:32 PM (16 minutes ago)

to me
You BOV should be fully closed at idle. With you vacuum at idle reading -18, you should be using our Plain spring for sure. The black spring is too weak to keep the BOV closed. Sounds like you are not losing any unmetered air, but you're boost response time will be quicker with the BOV closed. Try to get the Plain spring installed if you can.

Regards,

Ian
TiAL Sport
 

xXAzureMach1Xx

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I'm no expert but if the bov is closed at idle and it needs to be closed under wot, will it ever open? Mine is open at idle. When I give it some gas it closes. It's designed to open after boost to bleed off the boost to keep it from pushing back through the turbo. So if it's closed under vac and closed under boost then will it open? Pulling air from bov is still meter air and it wouldn't be a vac leak because it is before the tb.
 

MTBSully

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I'm no expert but if the bov is closed at idle and it needs to be closed under wot, will it ever open? Mine is open at idle. When I give it some gas it closes. It's designed to open after boost to bleed off the boost to keep it from pushing back through the turbo. So if it's closed under vac and closed under boost then will it open? Pulling air from bov is still meter air and it wouldn't be a vac leak because it is before the tb.

Read the email above. As long as it is before the MAF, it won't be unmetered air, but if your BOV is open at idle, your boost response time is slightly slower (Turbo starts to spool, but BOV is open which lets boost out).

Ideally, your BOV should be closed at idle, closed in boost, and open after the TB blades shut. Check out this video that shows correct operation:

Tial 50mm BOV in action - YouTube

Like I said, it will still work if the BOV is open at idle as long as it is before the MAF, but for $15 and abut 5 minutes to swap to the correct spring, I figured it was worth it.
 

sunburned

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I'm no expert but if the bov is closed at idle and it needs to be closed under wot, will it ever open? Mine is open at idle. When I give it some gas it closes. It's designed to open after boost to bleed off the boost to keep it from pushing back through the turbo. So if it's closed under vac and closed under boost then will it open? Pulling air from bov is still meter air and it wouldn't be a vac leak because it is before the tb.

The whole point of the spring is to counteract the vacuum at idle. So when the car is sitting idling, the vacuum wants to pull open the valve, but the spring doesn't let it. This lets your intake system function as normal. When you get under boost, the charge pipe can pressurize immediately because the valve is closed and the boost in the vacuum line holds the valve closed. When you let off the gas, all of a sudden you have the boost pressure in the charge pipe and the vacuum in the vacuum lines trying to open the valve, so it pushes past the spring pressure and opens.


The only reason you want a BOV that is open at idle is for a supercharger that is constantly spinning with the belt. It's creating pressure in the charge pipe even at idle, so you want that pressure to be vented. I had a Tial 50mm BOV on my T-trim setup and they have a very light spring specifically for superchargers that allows the valve to be open at idle. (That setup was LOUD)
 

Smacked_in_ATL

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Old thread but...

MAF based cars = needs to be closed at idle
MAP/Speed Density cars = doesn't matter/usually open at idle
 
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