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Old 04-27-2007, 01:53 PM   #1
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Default help with bov

I have a forge blow -off valve and I can see the valve opening, and it i put mu hand over it when it opens I can feel some air come out. Now this is on idle, but when I rev the motor and it releases the air the bov sound comes from the turbo side. Am I surging or what is going on?
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Old 04-27-2007, 02:02 PM   #2
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yeah that would be surging if you hear it comming from the turbo side.

how/where is your vacuum line hooked up? when you put your hand over it when you dump, can you not feel a lot of air blowing out? try to loosen the valve.
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Old 04-27-2007, 02:09 PM   #3
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Im taking vaccuum from the previously plugged port right behind the throttle bogy on top of the intake manifold. when I rev the motor the valve moves however the sound still comes from the turbo side
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Old 04-27-2007, 02:19 PM   #4
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can you verify the valve is opening when it dumps? watch it at idle, crank the **** out of the throttle....you should see it seal up better when you get on it, and then open rapidly as you let off....if it's not opening , try loosening the valve.
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Old 04-27-2007, 02:23 PM   #5
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it opens exactly as u described but the bov sound does not come from the bov it comes from the same side of the turbo. Could it just be my filter making the noise more noticable from the turbo side.... maybe there is not enuff load when revving it at idle, but it opens just as u descrivbed it should. Im just worried about the sound resulting in compressor surge.
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Old 04-27-2007, 02:26 PM   #6
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i mean, i hear some out of my filter....more now without the AFM....but if it sounds like a duck getting run over, then you know you have a problem...

this car does not have a BOV, this is surge: http://www.youtube.com/watch?v=nTnUaBWXm88

same here. no BOV = surge: http://www.youtube.com/watch?v=EnjUgYVwHSc&NR=1

what you're hearing is all the boost presuure going back through the turbo, the blades chopping up the compressed air, and the turbo blades spinning the opposite direction...
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Old 04-27-2007, 02:31 PM   #7
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mine sounds mothing like that so I guess im good.
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Old 04-27-2007, 05:05 PM   #8
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Which model do you have and what colour spring is in it? Also, how much boost are you running and what size is your vacuum line? Anything else tied into it?

We rate the springs as follows:
Black < 10
Green 5-15
Yellow 15-23
Blue 23-30
Red 30+

Look here and give me the part number:
http://www.forgemotorsport.com/conte...t&catalog=0006

There are a few valves that look identical externally but the internals differ enough to make them behave very differently.


If its a twin piston unit rev'ing without load you will see the aluminum piston lifting but there is a secondary plastic piston that will stay closed unless there is enough pressure in the charge pipe to lift the helper spring that is sandwiched between the two. Under load you will need to run the appropriate spring for the boost that you are running.

If its a single piton valve it will leak at idle but may not open enough under load if you have to stiff of a spring in there.
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Old 04-27-2007, 10:03 PM   #9
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When I drove with my hood off when the BOV would open and I would get a weird gobbling sound from the intake. I'd assume it's normal.

On a side note, would drilling and tapping a fitting in the intake manifold for a larger BOV hose be a good idea? My valve (Turbo XS type s) is non adjustable and doesn't open until 1-2 psi. I think the small port on the TB is too small, and I want to add a bigger fitting. Good idea?
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Old 04-27-2007, 10:37 PM   #10
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I have this one . I took it off an ausi s4 running 12 pounds of boost. I dont get the flutter compressor surge noise so im assuming that im good. guess im just not used to the bov sound yet.
http://www.forgemotorsport.com/conte...uct=FMDV001GTI
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Old 04-28-2007, 02:00 PM   #11
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Hmm, hopefully you have this one:
http://www.forgemotorsport.com/conte...roduct=FMDV004
They look the same but the one that linked you to won't work unless you are running a MAP sensor.

You need to disassemble the valve and check that it has two springs and two piston. Also need to know the colour of the larger spring.

Also perform the test and service procedure outlined here:
http://www.forgemotorsport.com/media...service(1).pdf



Larger pressure references can definitely have an impact on how a valve performs...
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Old 04-28-2007, 06:34 PM   #12
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i think it is the one u posted cuz it came of a maf s4
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Old 04-28-2007, 06:52 PM   #13
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Hopefully so. Do the test in the pdf and let me know what the spring is, if need be I can ship you a rebuild kit and a different spring.
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Old 04-28-2007, 07:05 PM   #14
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ok thanx
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Old 04-28-2007, 08:29 PM   #15
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Quote:
Originally Posted by miataspeed1point6 View Post
On a side note, would drilling and tapping a fitting in the intake manifold for a larger BOV hose be a good idea? My valve (Turbo XS type s) is non adjustable and doesn't open until 1-2 psi. I think the small port on the TB is too small, and I want to add a bigger fitting. Good idea?
I drilled and tapped mine. Works like a champ.
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