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BOV is opening under boost

Old 09-09-2018, 06:42 PM
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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, 07:58 PM
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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, 08:11 AM
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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, 09:42 AM
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Re: BOV is opening under boost

Originally Posted by 86CamaroDan View Post
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, 10:09 AM
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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, 10:24 AM
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Re: BOV is opening under boost

Originally Posted by Orr89RocZ View Post
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, 11:48 AM
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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, 12:32 PM
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Re: BOV is opening under boost

Originally Posted by DIGGLER View Post
do you not run a bypass valve?
Just a BOV vented to atmosphere.

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Old 09-10-2018, 01:54 PM
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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, 01:56 PM
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Re: BOV is opening under boost

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, 02:13 PM
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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, 02:24 PM
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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, 02:29 PM
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Re: BOV is opening under boost

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.

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Old 09-26-2018, 11:51 AM
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Re: BOV is opening under boost

I turned the screw clockwise a few turns, and now it's holding about 6psi.

It's funny, it just opens up and starts screaming lol.

I'll tinker with it a little more when I get back from vacation. I gotta clean out my trailer and maybe haul it up to the dragway before they close (end of October).

I've been driving the car as much as I can, and it's impressively reliable. Doesn't matter if it's 90 and humid, or 45 degrees out the temp stays the same, no issues. I'm kinda impressed.

No signs of belt slip, and it' hasn't walked or thrown a belt so I'm pretty happy about my rev3 blower brackets.

Over this winter I'm going to be designing some blower brackets for my buddy's LT1 thirdgen build. (he's ditching the turbo). The LT1 fbody accessories leave the entire driver side of the engine open, so I'm going to run a double plate bolted to the block and head. A spacer bolted to the LT1 crank hub with independent blower belt. MS2 in batch fire + CNP on a .040 over build LT1. Should be a cool build.

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Old 09-26-2018, 05:03 PM
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Re: BOV is opening under boost

Hmm, what's a blow off valve lol? Ported shrouds FTW, plus one for us turbo guys...

Originally Posted by anesthes
Over this winter I'm going to be designing some blower brackets for my buddy's LT1 thirdgen build. (he's ditching the turbo).
Heh, so your buddy is going from slow.... to slower, ehh? j/k

Looking forward to seeing some track pulls Joe...

- Rob
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Old 09-26-2018, 05:17 PM
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Re: BOV is opening under boost

Originally Posted by Street Lethal View Post
Hmm, what's a blow off valve lol? Ported shrouds FTW, plus one for us turbo guys...



Heh, so your buddy is going from slow.... to slower, ehh? j/k

Looking forward to seeing some track pulls Joe...

- Rob
Haha I think after 5 plus years of reading about the turbo build blowing up on here or them never getting completed I think he just wants something that's reliable and works lol.

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Old 09-26-2018, 06:02 PM
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Re: BOV is opening under boost

Originally Posted by anesthes
Haha I think after 5 plus years of reading about the turbo build blowing up on here or them never getting completed I think he just wants something that's reliable and works lol.
Hey hey, mine is done lol. Mind you its not going to run nine seconds the way it is at the moment, but it's definitely on the road. I'm running a ten pound spring in the gate, and am waiting on my electronic boost controller to dial it in through 9 to 16 pounds. Will see that much boost when the E85 is in, but keeping it capped at 10 pounds with pump gas and 10* spark advance. Also bought a Flex Fuel Sensor that is still pending install.... but the car is on the road though.

- Rob
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