Blow off Valve not sealing at idle
10-08-2007, 01:02 PM
#1
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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.
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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10-08-2007, 01:06 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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10-08-2007, 01:12 PM
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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
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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10-08-2007, 01:30 PM
#5
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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10-08-2007, 04:29 PM
#14
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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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10-08-2007, 09:43 PM
#15
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...
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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10-09-2007, 01:16 AM
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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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10-09-2007, 03:31 AM
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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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I thought you were smarter than to reply before thinking
insert foot and chew on toe nails bud. :gay:
