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BOV is opening under boost

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Old 09-09-2018, 05:42 PM   #1  
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BOV is opening under boost

Once I hit about 3psi (according to the ECU) I could hear the BOV squeling and boost wouldn't go up. My mechanical gauge showed nearly 5 psi but who knows.

Notice the jaggedness of the boost, yet RPM climbs.


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Old 09-09-2018, 06:58 PM   #2  
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Re: BOV is opening under boost

The rubber diaphragm might have a tear in it. If you have a vacuum pump, apply some vacuum to the vacuum port and see if it holds.
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Old 09-10-2018, 07:11 AM   #3  
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Re: BOV is opening under boost

what type of valve? sure it flows enough for the application?
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Old 09-10-2018, 08:42 AM   #4  
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Re: BOV is opening under boost

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what type of valve? sure it flows enough for the application?
Greddy type S. Not sure, but the problem isn't not enough venting, the problem is it's opening under boost. Which is odd cuz you'd think even if the spring didn't keep it closed the pressure on the vac line would.

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Old 09-10-2018, 09:09 AM   #5  
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Re: BOV is opening under boost

Yeah the vacuum line side is suppose to equalize pressure to help keep it closed. Is it tee’d into another source or on its own? Put it on its own. Check line and internals of bov
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Old 09-10-2018, 09:24 AM   #6  
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Re: BOV is opening under boost

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Yeah the vacuum line side is suppose to equalize pressure to help keep it closed. Is it tee’d into another source or on its own? Put it on its own. Check line and internals of bov
IT's on it's own source. It has an adjustment on the top "hard ---- soft".. I wonder if maybe it's backed out too much?

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Old 09-10-2018, 10:48 AM   #7  
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Re: BOV is opening under boost

do you not run a bypass valve?
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Old 09-10-2018, 11:32 AM   #8  
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Re: BOV is opening under boost

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do you not run a bypass valve?
Just a BOV vented to atmosphere.

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Old 09-10-2018, 12:54 PM   #9  
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Re: BOV is opening under boost

need a bypass valve that can open at idle with a supercharger. i would swap it out.
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Old 09-10-2018, 12:56 PM   #10  
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Re: BOV is opening under boost

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Originally Posted by DIGGLER View Post
need a bypass valve that can open at idle with a supercharger. i would swap it out.
It opens at idle, or whenever there is more than 10hg or so of vac on it.

A bypass valve recirculates into the air cleaner, or at least that's the definition I've always gone by. (see below)

https://www.turbobygarrett.com/turbo...bov_and_bypass

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Old 09-10-2018, 01:13 PM   #11  
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Re: BOV is opening under boost

Yeah spring rate should be enough to keep valve shut until vacuum opens it.
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Old 09-10-2018, 01:24 PM   #12  
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Re: BOV is opening under boost

if its somewhat open at idle you are good. im talking about something like a vortech mondo valve or something. you can actually adjust the vacuum where the valve opens up at idle/part throttle on those, not a pressure where it opens, since you would usually adjust boost psi with your pulleys/blower size. i know the mondo fore sure opens at idle.
you could plumb either bypass or bov to vent back into the intake piping technically making them "bypass".

now that i think about it, the way a mondo is made, boost pressure actually forces the valve closed more and more as pressure goes up.
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Old 09-10-2018, 01:29 PM   #13  
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Re: BOV is opening under boost

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Originally Posted by DIGGLER View Post
if its somewhat open at idle you are good. im talking about something like a vortech mondo valve or something. you can actually adjust the vacuum where the valve opens up at idle/part throttle on those, not a pressure where it opens, since you would usually adjust boost psi with your pulleys/blower size. i know the mondo fore sure opens at idle.
you could plumb either bypass or bov to vent back into the intake piping technically making them "bypass".

now that i think about it, the way a mondo is made, boost pressure actually forces the valve closed more and more as pressure goes up.
This valve appears to be designed the same way. It should have pressure in the top when under boost to keep it closed. Yet it's opening. In fact, at about 3psi it's screaming.

Otherwise, the car seems really reliable. Just need to tinker with the valve a little bit, and clean out my trailer. I'm hoping to get some passes at the track during October.

-- Joe
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