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Old 10-08-2007, 02:02 PM   #1
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Default Blow off Valve not sealing at idle

If I tighten my BOV so it seals at idle, it never opens with boost. If I soften it so that it cracks open with idle, it dumps to atmo as needed, except for on the very lightest of throttle lifts. I cut a couple coils off the spring and readjusted, but same thing. Can't make it seal up at idle without rendering it useless.

So, there is an incredible amount of vac in the top of the BOV. What I was considering is placing a vac restrictor in the signal line, hoping that I get less suction at idle.

The only drawback I can think of, is that with less vac on the signal, I might not get blow off under some light throttle lifts... but at least the thing would seal at idle.

My second plan is to find some sort of foam filter I can wrap around the BOV.
Thoughts? I dissasembled, cleaned, and oiled it today, so please don't tell me that.
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Old 10-08-2007, 02:06 PM   #2
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In my opinion I think the bov should be open at idle in order to function properly. I put a little K&N on mine. For my setup I needed a very slight difference in pressure to open the BOV or else my turbo's would cavitate/gobble. So at idle, where there's a pretty large difference in pressure on either side of the valve, my BOV is almost fully open.
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Old 10-08-2007, 02:12 PM   #3
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Thanks Tim. If my valve is set a little softer and fully open at idle, I belive I get absolutely no surge ever, even on the lightest throttle lifts.

Problem with simply adding a filter to my valve is it vents through holes in the long side of the cylinder, not through an opening in the short side like others. Not terribly clear in the pic, but if you look close you can see the copper colored valve through the holes in the outer case:
https://www.miataturbo.net/vbgarage....etimage&id=645
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Old 10-08-2007, 02:19 PM   #4
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boost/vac and vac only source ftw.

Last edited by Braineack; 10-08-2007 at 02:42 PM.
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Old 10-08-2007, 02:30 PM   #5
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Why would you want you BOV open at idle? My tial's spring is super heavy, if i take the BOV off and try to compress the piston i just about get a brain anneurism. It doesn't leak at idle, if I rev it up a little at the throttle body I can see it open a little when I let off though, it definitely has no problems opening under very light boost. I tapped the manifold and it has it's own dedicated vac source.
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Old 10-08-2007, 02:57 PM   #6
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boost/vac and vac only source ftw.
yup.
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Old 10-08-2007, 04:12 PM   #7
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Quote:
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boost/vac and vac only source ftw.
?
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Old 10-08-2007, 05:09 PM   #8
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?
two port bov hooked to both sides of the throttle body...
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Old 10-08-2007, 05:13 PM   #9
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all this talk is confeusing the crap out of me,can someone tell me if this bov will work for me if im running MS on MAP? im so confeused about this open closed crap...so please help
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Old 10-08-2007, 05:16 PM   #10
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if your running a map it doesnt matter if its open at idle. open at idle is only an issue for us with the afm/maf still
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Old 10-08-2007, 05:18 PM   #11
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if your running a map it doesnt matter if its open at idle. open at idle is only an issue for us with the afm/maf still
...and/or those who do not want to suck unfiltered air into their engines
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Old 10-08-2007, 05:20 PM   #12
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thanks man, i was starting to get scared, i just got it yesterday
so why does it stay open? i though it was only supposed to open up to went off excess boost...sorry for the newb question, i never had boost, obviously
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Old 10-08-2007, 05:26 PM   #13
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...and/or those who do not want to suck unfiltered air into their engines
unfiltered air is where it's at!
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Old 10-08-2007, 05:29 PM   #14
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Originally Posted by whaaamx5 View Post
thanks man, i was starting to get scared, i just got it yesterday
so why does it stay open? i though it was only supposed to open up to went off excess boost...sorry for the newb question, i never had boost, obviously
it is connected to a vac line. under vac it sucks open, under boost it helps to keep it closed. when you shift, the boost still in the charge pipes and the vac from the engine opens it more
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Old 10-08-2007, 10:43 PM   #15
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Any o-rings in the valve? You can try removing some/all of them.

Restrictor is another way... or you can try running a very light spring in it, place a T in the reference, and run two lines with check valves in them. Each faced a different way. This allows you play around with reference location and restictors on the boost and vac references independently...

Or either sand down the outer surface of the piston or drill a hole in the center of it... the later you can un-do with a touch of J-B or a grub screw... if you get this right the valve will open initially but the vac will bleed down at idle allowing the valve to close...

Or you can try a secondary spring and piston beneath the primary like the atmo valves that we make. At idle the primary is lifted but the secondary stays shut...
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Old 10-09-2007, 02:16 AM   #16
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That's good stuff Pat, thanks. I'll start with the less extreme, ie modifying the signal line, but if that doesn't work I like the idea of drilling through the piston. Good call.
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Old 10-09-2007, 04:31 AM   #17
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I'm starting to sound like a broken record here. Get a Megasquirt and just delete the stupid MAF. I don't even know if my BOV leaks at idle or not and I could care less.
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Old 10-09-2007, 06:50 AM   #18
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Quote:
Originally Posted by Savington View Post
I'm starting to sound like a broken record here. Get a Megasquirt and just delete the stupid MAF. I don't even know if my BOV leaks at idle or not and I could care less.
I thought you were smarter than to reply before thinking
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Old 10-09-2007, 09:00 AM   #19
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Quote:
Originally Posted by Savington View Post
I'm starting to sound like a broken record here. Get a Megasquirt and just delete the stupid MAF. I don't even know if my BOV leaks at idle or not and I could care less.
insert foot and chew on toe nails bud. :gay:
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Old 10-09-2007, 09:19 AM   #20
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Quote:
Originally Posted by y8s View Post
two port bov hooked to both sides of the throttle body...
I see, I've only used standard one port BOV's. So wouldn't it then be "boost/vac (after TB) and boost only (before TB)"?
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