Blow off Valve not sealing at idle
#23
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edit: wait wait it would see vac on both sides as you approach WOT. just not very much vac.
#24
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So back to the initial answer, for a typical BOV to function properly (at least my opinion of properly) you need a small spring pressure, just enough to "hold the thing closed when the pressure on both sides of the" *piston* "is equalish". This means it's open at idle.
I never played with a diaphram BOV but I assume it's like a two port wastegate, one port on each side of the diaphram right? Still need a light spring though. How then could a diaphram type be closed at idle with a light spring preload? At idle, the high vacuum would suck the top of the diaphram up, opening the valve.
If you have a BOV like Ben with ports all around the outside, I dunno how you'd seal it. My old Turbosmart was like this. I couldn't get a soft enough spring to get it to work like described above so I never used it.
#25
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My Chinese knock-off of a Greddy Type-RS falls into the latter category. As delivered, the springs (plural) were so stiff that the valve was fully closed at idle, and didn't do its job very well. Removing the smaller of the two springs caused the valve to leak significantly at idle, but close as soon as MAP rises a few inches. It does not leak under boost, but vents even when you lift off the throttle slightly from non-boosted cruise. I lathed an adapter to install a K&N filter on the outlet which muffles the sound a bit and makes me not care about the idle leak.
#26
BOV 101...seriously good thread, i wish i could chime in but im on the learning side here and i am glad to hear this stuff now
since my setup will not be installed until after i get the car to run on MAP, i really have nothing to worry about other than unfiltered air...if this is incorrect someone slap me now...
would it be wise to make some kind of maybe thin foam filter to fit snug around my BOV for daily driving, i dont see much affect on function in this case...any thoughts?
Thanks
Dan
since my setup will not be installed until after i get the car to run on MAP, i really have nothing to worry about other than unfiltered air...if this is incorrect someone slap me now...
would it be wise to make some kind of maybe thin foam filter to fit snug around my BOV for daily driving, i dont see much affect on function in this case...any thoughts?
Thanks
Dan
#28
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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...
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...
#29
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Exactly. I'll agree with that. And this is also how standard one port/piston BOV's work, just that the second port is the inlet/bottom of the piston.
So back to the initial answer, for a typical BOV to function properly (at least my opinion of properly) you need a small spring pressure, just enough to "hold the thing closed when the pressure on both sides of the" *piston* "is equalish". This means it's open at idle.
I never played with a diaphram BOV but I assume it's like a two port wastegate, one port on each side of the diaphram right? Still need a light spring though. How then could a diaphram type be closed at idle with a light spring preload? At idle, the high vacuum would suck the top of the diaphram up, opening the valve.
If you have a BOV like Ben with ports all around the outside, I dunno how you'd seal it. My old Turbosmart was like this. I couldn't get a soft enough spring to get it to work like described above so I never used it.
So back to the initial answer, for a typical BOV to function properly (at least my opinion of properly) you need a small spring pressure, just enough to "hold the thing closed when the pressure on both sides of the" *piston* "is equalish". This means it's open at idle.
I never played with a diaphram BOV but I assume it's like a two port wastegate, one port on each side of the diaphram right? Still need a light spring though. How then could a diaphram type be closed at idle with a light spring preload? At idle, the high vacuum would suck the top of the diaphram up, opening the valve.
If you have a BOV like Ben with ports all around the outside, I dunno how you'd seal it. My old Turbosmart was like this. I couldn't get a soft enough spring to get it to work like described above so I never used it.
#30
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In the single-port models, I expect that to a certain extent the manifold pressure acting upon the bottom of the valve itself serves somewhat the same function as the lower port otherwise would.
Also, I'll add that the range of adjustment provided by the screw on the top of mine was very small. When both springs were in, the adjuster seemed to do nothing at all- it was always too tight. With the center spring removed, the adjuster is useless on the opposite end of the spectrum- it always leaks at idle. I simply set it to "fully tight" which translates to "leaks a bit less at idle, and doesn't leak under boost." There's room on the inside to shim the spring a bit, should an application require. It might be possible to eliminate the idle leak this way, though at the risk of binding the spring and reducing valve travel.
A hand-operated vacuum pump (with gauge) is a useful tool for bench-testing. My typical idle vacuum is around 20", so I produced 20" with the pump and played with the BOV.
Also, I'll add that the range of adjustment provided by the screw on the top of mine was very small. When both springs were in, the adjuster seemed to do nothing at all- it was always too tight. With the center spring removed, the adjuster is useless on the opposite end of the spectrum- it always leaks at idle. I simply set it to "fully tight" which translates to "leaks a bit less at idle, and doesn't leak under boost." There's room on the inside to shim the spring a bit, should an application require. It might be possible to eliminate the idle leak this way, though at the risk of binding the spring and reducing valve travel.
A hand-operated vacuum pump (with gauge) is a useful tool for bench-testing. My typical idle vacuum is around 20", so I produced 20" with the pump and played with the BOV.
#31
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I would think so as well. Either way you'd think having a diaphram type would be harder to tune, because you have different amount of pressure area on each side of the BOV. But if it's designed correctly it could work better...hmmm I'll have to think about that.
#32
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I dunno what rate spring you need--i can push mine open by hand. it's not easy but I can. it's also adjustable. but the spring must be enough to just barely hold it closed at ~20" of vacuum in the mani and slightly below atmospheric in the charge pipe. as soon as I get to 0 psi, it'll blow off when I close the throttle/lift.
#33
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So long as you are not running an AFM/MAF sensor, and you have some provision for placing a filter on the outlet, I think that a VTA diaphragm design is the way to go. They respond very quickly, are cheap, fairly easy to set up, and require zero maintenance. Even if the quality of my little Chinese unit turns out to be garbage and the diaphragm ruptures after a year, it only costs about $35 to chuck it and buy a new one.
Those who are using airflow sensors can recirculate with a minimum of extra parts.
#35
Wow, I never figured you could have problems with your BOV... All I did with my Forge Motorsport Dual Piston was install it, and forget it, and enjoy the sweet sounds it makes. Yes it's a little more expensive, but after reading all this I think it's worth it instead of the hassle the cheaper ones can be.
#37
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It is a cheap Chinese copy of a Greddy Type RS BOV, of the sort sold by many different vendors on eBay. Here is an example of one:
http://cgi.ebay.com/ebaymotors/Type-...QQcmdZViewItem
And here is the Real Deal™: http://www.greddy.com/products/displ...SubCategory=18 (first one on the list)
While the quality of Chinese-made products in this sector of the market is reputed to vary considerably, the BOV that I received was quite nice. The machine work on the important surfaces was very good- only problem was that the springs were too stiff. Solving this simply entailed the removal of the smaller of the two springs. For anybody planning to recirculate, or for VTA on cars with no AFM/MAF (and with a filter on the outlet) I'd highly recommend it.
http://cgi.ebay.com/ebaymotors/Type-...QQcmdZViewItem
And here is the Real Deal™: http://www.greddy.com/products/displ...SubCategory=18 (first one on the list)
While the quality of Chinese-made products in this sector of the market is reputed to vary considerably, the BOV that I received was quite nice. The machine work on the important surfaces was very good- only problem was that the springs were too stiff. Solving this simply entailed the removal of the smaller of the two springs. For anybody planning to recirculate, or for VTA on cars with no AFM/MAF (and with a filter on the outlet) I'd highly recommend it.
#39
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However, if you shop around you'll find that some of the BOVs sold on eBay (mostly the twin-port Type S models) include an integral exhaust flange, such as this one: http://cgi.ebay.com/ebaymotors/Turbo...QQcmdZViewItem
And you can also find the screw-in version for the Type RS separately from some vendors.
http://cgi.ebay.com/ebaymotors/Gredd...QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/GREDD...QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/GREDD...QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/GREDD...QQcmdZViewItem
#40
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Been screwing around with this thing. I softened up the spring it came with enough so that it would blow off w/o surge, but that resulted in a big boost leak when pressurized. And it was still open at idle, letting in unfiltered air.
Added a second spring today. It's the same lenght as the existing spring was, and pretty soft in comparison, but is small in circumfrence so it fits inside the main spring. Now the BOV is sealed at idle and doesn't leak under boost. What I sacrificed was I still don't get any blow off during small lifts where MAP is around atmo, and I get a small amount of surge there. Otherwise, it's fine. Certainly better than before.
Added a second spring today. It's the same lenght as the existing spring was, and pretty soft in comparison, but is small in circumfrence so it fits inside the main spring. Now the BOV is sealed at idle and doesn't leak under boost. What I sacrificed was I still don't get any blow off during small lifts where MAP is around atmo, and I get a small amount of surge there. Otherwise, it's fine. Certainly better than before.