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. :)

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.

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

boost/vac and vac only source ftw.

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.

yup.

?

two port bov hooked to both sides of the throttle body...

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
Attachment 215705

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:eek5:

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

unfiltered air is where it's at!

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

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...

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.

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.

:rofl: I thought you were smarter than to reply before thinking

:D insert foot and chew on toe nails bud. :gay:

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)"?

Wait, Savington, you could care less? So, you're not at the full extent of your lack of caring with regard to the current configuration?

Who were you talking to?

yeah it would. and it makes the spring force more or less irrelevant as long as it can hold the thing closed when the pressure on both sides of the diaphragm is equalish.

edit: wait wait it would see vac on both sides as you approach WOT. just not very much vac.

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.

Some of them have ports on both sides of the diaphragm, others have a port only on the top of the diaphragm, and a vent which is open to atmosphere on the bottom.

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.

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

Really? Wow. OK thanks.

I just tried this. It worked to hold the valve shut at idle. However, it now fails to hold the valve shut after 10 psi so it leaks boost to atmo. This is with a restrictor on the vac line, but no restrictor on the boost line. It was a good idea though.

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.

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.

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.

Mine's the same, it barely closes at idle. Sometimes it's a tad slow and i can hear it close (makes a little whistle). However if I tighten the preload anymore it tends to flutter under light dumps, which I absolutely can't stand.

Well, it is considerably easier to tune than my old piston-style FM BOV (not the GFB one, This One). That particular BOV was impossible to tune because it didn't work. No matter what I lubricated that damn piston with, it'd seize up within a few weeks, requiring that I dismantle, clean, and re-lubricate it. My current BOV has been in for about six months, in which time I have not touched it once. It vents when it's supposed to, and it never, ever flutters. Ever.

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.

Just a note to the OP. Cutting the spring is going to increase the spring rate.

Joe: Which BOV do you have (or did I miss that)?

-Mike

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.

I second joes hand pump idea i adjusted mine to where it took about 2-3 lbs of force to open it i if had a vac of 15-20. Then after reinstaling it the unit has been trouble free ever since.

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.

Joe, You own a lathe don't you?
You should make a few of those filter adapters and sell them. I'd take one :)
I'm tired of screwing with this BOV.

I do have a small lathe (7x12) however I found the process of turning that adapter to be extremely tedious. I couldn't find any pipe in the correct diameter, so I started with a one foot long piece of solid 2 3/8" round bar stock. That thing took forever to bore out and turn down to the proper size. It was fun to be able to say that I made my own adapter, however I have no intention of going into business with them. I think I've got a picture at home of the raw bar sitting next to the finished piece- it's amazing.

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

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. :mad:

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.

and went to dinner in the miata... and the fucking BOV didn't vent at all, even at 16 psi. :vash: It was working fine when I parked it this afternoon. :confused:

What do you use to lube the piston? I gave it a light coating of Mobil1 10-30 last week.

Seems like you're having a similar problem with the GFB as I had with the older-style FM BOV. I've just really come to dislike piston type BOVs in general. My el-cheepo Greddy knockoff has served me very well so far.

BTW, I found the picture of the adapter I made. From left to right are the original horn that came with my BOV, the adapter I lathed to accept the K&N filter, and the big hunk of solid aluminum that I made the adapter from. What a pain that was...
http://img522.imageshack.us/img522/3841/adapterum6.jpg

Hmm. Let me explain a bit more to see that we are on the same page. Two lines going to the intake manifold with check valves, the check valves facing different ways. So one line will allow boost to reach the top of the valve and one allowing vacuum. But both from the same source... Is that how you did it or do you have the vac line run to a constant vac source?

Also, you mentioned getting a boost leak when you soften the spring tension. Are you testing just by pressurizing the charge pipes or are you getting boost pressure to the top of the valve as well? You need to do the second if you aren't...

http://img140.imageshack.us/img140/6841/bovdq1.png

testing by going out and putting my foot down

lol