1g bov diagram?(How BOV works inside)

Does anyone have one? I have one for the Greddy Type S but I need the 1g.
http://www.935motorsports.com/greddybov.htm

What do you need it for? 1G is the same thing except the "lower port" is cast into the BOV and the source is the UICP (the hole next to the valve on the flange side of the BOV). Many poeple intercept that port and put a mipple on it, which make it function like the greddy in a way. We tend to use DSMlink or a switch to control when that lower port sees atmosphere and when it sees boost. Getting OT I guess though. :)

I'm just trying to figure out the 1g bov ringing that me and some others have had to deal with. If I knew how the thing worked exactly then maybe I could find a way to fix it. Even if I can't fix it, it would still be interesting to know what all the parts inside are. Here's a pic of mine through the dump tube opening. Just kind of wondering if anything in there could be ringing or if it's something in the top portion of the bov. Does it use a rubber seal on the bottom of the valve or is it just metal on metal (better than 2g and evo plastic on plastic lol)?

http://img.photobucket.com/albums/v358/Nayr747/1gbov.jpg

What do you need it for? 1G is the same thing except the "lower port" is cast into the BOV and the source is the UICP (the hole next to the valve on the flange side of the BOV). Many poeple intercept that port and put a mipple on it, which make it function like the greddy in a way. We tend to use DSMlink or a switch to control when that lower port sees atmosphere and when it sees boost. Getting OT I guess though. :)

I've never read anything about that hole or using DSMlink to change how the valve acts. That's crazy, learn something new every day. This is the port you're talking about right, the small hole by the valve?
http://i8.ebayimg.com/03/i/05/0f/9a/06_1.JPG?set_id=7

ummm...DSMlink doesn't control anything to do with that port..

At least I've never heard of it.

Correct me if I'm wrong Kevin?

I'll correct you, because you are wrong :icon16: I posted it in the previous thread. You put a 3 way solenoid on that port to switch between boost (in the UICP) and atmosphere. You can use a WOT switch or DSMlink's nitrous controls to trigger that solenoid when you want. SOme poeple also only put that port to atmosphere at the track, and run it normal on the street, etc, with a simple switch.

Dejon now overs this as some leak stop mod or something, and tested it to over 30 psi. This was originally done by Gus Mahon, hence the term "Gus modded BOV." There is probably still a page up on gary donovans site, I think it was www.thedodgegarage.com. Hmm, stills links to his page but the link is broken. Gus unfortunately passed away a few years ago after a motorcycle accident, they must not have maintained his page. I could have sworn they did though.

I think this is what you're talking about.
http://www.thedodgegarage.com/turbo_bov_mod.html
I've had that page saved for a while but never got around to reading it. Thought it was an alternative to crushing. Anyone seen this page? Haven't read the whole thing but it seems interesting.
http://autospeed.drive.com.au/A_2181/cms/article.html

Ok so I don't get what the point of that port/chamber even is on the 1g or type s. Does boost pressure in that chamber really help move the valve up? Isn't the boost on the botom of the valve already doing that? Or does the surface area that the boost is pushing on matter? Also, I'm guessing plugging that port would be a very bad idea for your turbo's health since the valve wouln't be able to move up and down very easily causing surge. And the diaphram would have to be forced down to make the air volume in the chamber the same. I think I read a post on tuners where people were saying to plug that and someone else said that's probably why their type s' diaphram was messed up.

Well on the ringing issue, don't know if you've ever experienced it but I'm just wondering what the cause is. I've already ordred a new bov so I'll probably cut the top off my old one to see what the internals are. Maybe I'll make a diagram since one doesn't seem to exist.

Yes, that is the page I am talking about.

You basically have 4 forces acting on the BOV.

-Pressure or vacuum on the top of the diaphram
-Pressure on the bottom of the diaphram via that lower port
-Pressure on the underside of the valve itself
-Spring pressure on the top of the diaphram

The combination of these forces is what determines the bahavior of the BOV. I'm trying to think of a short way to describe all of the typical situations, but I don't think there is one. The key point though is that the valve and diaphram are not the same size. The force on each is different at the same pressure since force = pressure times area. The diaphram is always larger than the valve, giving it more control over the BOVs actions than the valve. If the diaphram is twice the size of the valve, and there is 20 psi of boost (so 20 psi on the top of the diaphpram and 20 psi on the bottom of the valve), the valve will stay shut since there is double the force holding it shut. Also add in the spring pressure trying to hold it shut.

The problem is that the lower port allows the same boost pressure to reach the bottom the of the diaphram trying to open the valve. It effectively cancels the pressure on the top port, leaving only the spring pressure to hold the valve shut. If this was a static system it would still stay closed, but pressure in the IC piping (lower port) and in the manifold (upper port) is always varying, and at different rates. So the BOV tend to open at some pressure differential.

The purpose of the lower port, also called the fast release port, is to open the BOV more quickly when the throttle plate closes. Vacuum will build up on the top of the diaphram pulling the valve up, and pressure will spike in the UICP pushing on the valve (remember that is is ~half the size of the diaphram) AND on the lower part of the diaphram, opening it quickly. And in fact, putting atmosphere on that lower port will slow down the valves reaction time, and the valve/turbo become very noisy. And I agree that you would never want to cap off the bottom of the diaphram, as it would hinder movement of the diaphram.

This is where the solenoid switching comes into play. With the lower port at atmosphere you have both spriung pressure AND boost pressure on the top port pushing the valve closed, with only the smaller force on the valve to try to act against it and open the valve. It will hold extremely high amounts of pressure in this configuration. Most poeple stop testing at 35 psi or so. So at WOT (switch on throttle body) or under boost (hobbs pressure switch) the solenoid puts atmosphere on the bottom port, but when you let off it switches over and puts boost pressure from the UICP back on that port. DSMlinks nitrous controls can also be used to switch the solenoid. So you get the best of both worlds. Fast release when you let off, but excellent boost holding capacity at WOT.

Hopefully that helps to explain it.

I'm gonna sticky this and change the name a bit.

So, say like on the Greddy Type-S, should I hook up a vac line and t it into the line from the turbo to the wastegate? It says to do that one one write up for installing the type s on vfaq, but alot of people I know never did that.

Wow, thanks a lot for all the info kevin. After reading what you wrote (had to do it a couple times like aways with your posts), I think I almost get it. I'm still a little confused on a couple things like how exactly the valve acts/ what forces are acting on what parts under all the conditions that can occur.

Then there's this thread. Sorry, this is long. http://forums.evolutionm.net/showthread.php?s=&threadid=24611&highlight=bov
This just brought up more questions. Basically he says to take one of the springs out of the type s to make the pressure lighter.

"Getting a BOV with the largest valve to actuator diaphram ratio and then finding the optimum spring tension will be the best situation regarding the BOV."
"if you get a valve where the actuator piston surface area is larger than the valve area you should not need to use a heavy spring tension to get the valve to close quickly and completely."
"This valve [type s] seals completely even with as little as 6 PSI on the actuator and 20 PSI on the valve"
"even with the spring tension adjustment all the way out the Greddy needed almost 22” of vacuum [to open] (this could be a problem)."
"with the smaller lighter spring the valve seals with 20PSI on the valve and 14 PSI on the actuator (that works) and now the valve starts opening with only 8” of vacuum on the actuator(sweet!). With the larger individual spring the valve remained sealed with 20PSI on the valve and 12PSI on the actuator, under vacuum the valve starts opening at 12” of vacuum (still better than stock)."

So running the sype s with bottom chamber open to at. and lighter spring would work perfectly? I was thinking about it and the only action of the spring should be to keep the valve shut when no other forces are acting on the bov (boost/vaq). Anytime you're boosting, the larger diaphram area will keep the valve closed and when you let off the throttle the vaccum in the manifol will immeditely open the vlave because it doesn't have to fight a heavy spring. And applying that to a 1g bov, you could do the "Gus mod" and leave the lower chamber open to at. and the bov would funtion just like the modded type s (already having a lighter spring I think). And both bov's would hold any boost pressure without leaking. He said the same about the type s:

"People keep saying these valves leak at higher boost levels, but I cannot really understand how or why? If you have 30 PSI on the valve and 30PSI on the actuator piston (that has a larger diaphram area) there is no way the valve should leak."

These people might have the bottom port connected to boost though which would allow it to leak at boost that overwhelmed the spring right?

"I believe where the spring loading comes into play is really only during the transition points (I may be stating the obvious here but..). As the turbo is spooling up it is possible that the valve will see a higher presure than the actuator, with a very light spring tension I could imagine the valve might leak during this time, increasing turbo lag."

How would the valve see higher pressure?

I also dont understand the "pull type" / "push type" debate. Does the SSQV really funcion better than the push types?

Some helpful info for type s owners and 1g bov owners:

"The adjustment screw should be almost all the way out , there is a round plate that the spring sits in, the adjustment screw sits in an indentation on that plate. I put the aadjustment screw in far enough to keep that plate centered, that plate is what compresses the spring. You never want to get that adjustment screw down to far because it begins to limit the travel/opening of the valve."

"[1g bov] does seem to have a good valve to actuator diaphram ratio, and a rubber seal on the valve."
"[1g bov's] start blowing open around 18 psi, but they have no surge at all and blow off easily."

Oh, then someone said this:

"I am fortunate to live literally around the corner from Rhys Millen Motorsports. After a long discussion with the techs, the conclusion was NO advantage to a BOV. They routinely race rally-prepped cars with 400+ hp and have yet to need a BOV. A good turbo upgrade and free-flowing air are the biggest contributors to performance. If you want to hear that "whoosh" noise, play Gran Turismo...."

What is that about?

Wow, thanks a lot for all the info kevin. After reading what you wrote (had to do it a couple times like aways with your posts), I think I almost get it. I'm still a little confused on a couple things like how exactly the valve acts/ what forces are acting on what parts under all the conditions that can occur.

Sweet...

Then there's this thread. Sorry, this is long. http://forums.evolutionm.net/showthread.php?s=&threadid=24611&highlight=bov
This just brought up more questions. Basically he says to take one of the springs out of the type s to make the pressure lighter.

I've seen that thread. Some of the things he says, I'm not sure are accurate, but it's hard to tell. Might just be in the wording.

"Getting a BOV with the largest valve to actuator diaphram ratio and then finding the optimum spring tension will be the best situation regarding the BOV."

Yes. The larger the difference in those ratios, the less likely it will be to open with just "under the valve" pressure. A diaphram 3 times larger than the valve for example would provide 3 times the force holding it closed under boost than the force pushing up on the valve.

"if you get a valve where the actuator piston surface area is larger than the valve area you should not need to use a heavy spring tension to get the valve to close quickly and completely."

This is true, but the ratio isnt big enough to cover you in all cirmcumstances and a strong spring is still necessary. IMO, the spring pressure should be based directly on the vacuum the motor pulls. Run a crushed 1g BOV on a car with cams and its much noisier than the same BOV on a car with stock cams. More vac to pull it open quickly. In fact, the vac alone should be able to open the valve with no assistance from pressure under the valve.

"This valve [type s] seals completely even with as little as 6 PSI on the actuator and 20 PSI on the valve"
"even with the spring tension adjustment all the way out the Greddy needed almost 22” of vacuum [to open] (this could be a problem)."
"with the smaller lighter spring the valve seals with 20PSI on the valve and 14 PSI on the actuator (that works) and now the valve starts opening with only 8” of vacuum on the actuator(sweet!). With the larger individual spring the valve remained sealed with 20PSI on the valve and 12PSI on the actuator, under vacuum the valve starts opening at 12” of vacuum (still better than stock)."

These are good tests, but this is what I was refering to when I differentiated between static systems and the more dynamic system we have in the engine bay. Pressures are not the same at all points in the system, and there are delays in pressure changes that vary at different parts of the system. You might have 20 psi at the manifold, but have 24 psi in the UICP and 28 psi in the LICP, etc. Poeple have actually logged these differences too. Add into the mix a throttle valve that is constantly opening and closing, and turbo that is spooling up and down, an IC that has pressure drops that vary with changes in flow, etc. So we tend to need more spring than usual to keep the valve shut, especially when the diaphram is 2 times the valve size or less.

So running the sype s with bottom chamber open to at. and lighter spring would work perfectly? I was thinking about it and the only action of the spring should be to keep the valve shut when no other forces are acting on the bov (boost/vaq). Anytime you're boosting, the larger diaphram area will keep the valve closed and when you let off the throttle the vaccum in the manifol will immeditely open the vlave because it doesn't have to fight a heavy spring. And applying that to a 1g bov, you could do the "Gus mod" and leave the lower chamber open to at. and the bov would funtion just like the modded type s (already having a lighter spring I think). And both bov's would hold any boost pressure without leaking. He said the same about the type s:

The spring is there to make up for the differences in pressure and delays in pressure changes between the diaphram and the bottom of the valve. They will never have the same pressures on them, and the pressure under the valve is going to be higher and sooner, since its before many restrictions and closer to the source of the pressure increase. Hopefully that made sense. So you really want the stiffest spring that your vacuum can still open. Tial offers 7, 9, and 11 psi springs for different setups. Remember that vac in inches of mercury is double pressure in PSI (1 psi is 2 "hg). So an 11 pound spring (22 "hg) works well with stock cams, while a car with 15" can hardly open the BOV. The 7 psi spring would be better. The lighter spring reduces the chances of it opening when you don't want it to. I think you said something along these lines in the middle of that paragraph, about the vac not having to fight a spring that is too heavy in comparison.

You are right about the Gus modded 1g BOV not leaking, but it will run like absolute crap, since it is so slow to open, whatever it's spring rate may be. The 1g BOV spring is pretty heavy even uncrushed.

"People keep saying these valves leak at higher boost levels, but I cannot really understand how or why? If you have 30 PSI on the valve and 30PSI on the actuator piston (that has a larger diaphram area) there is no way the valve should leak."

It should be pretty leak tight with the lower port to atmosphere.

These people might have the bottom port connected to boost though which would allow it to leak at boost that overwhelmed the spring right?

Right. By removing the diaphram from the equation (roughly, pressure on both sides will not be equal, more below it in fact) all thats left is the spring. Add in the fact that pressure will be higher below the valve and diaphram, and that that pressure diferential will go up as boost goes up, and you will get some pressure that it starts to leak at. But in these cases, with pressure under the diaphram to blow it open, you can run a stiffer spring than you can on a BOV with the lower port at atmosphere.

[/quote]"I believe where the spring loading comes into play is really only during the transition points (I may be stating the obvious here but..). As the turbo is spooling up it is possible that the valve will see a higher presure than the actuator, with a very light spring tension I could imagine the valve might leak during this time, increasing turbo lag."[/quote]

He is right that its partly about transitional periods (valve being closer to the source than the diaphram), but it happens more often than just when the turbo spools up.

How would the valve see higher pressure?

For the reasons mentioned above. The valve is right after the turbo with just the FMIC before it, but boost then has to go through the TB, manifold, small vac port, long small line to the diaphram, etc. Also consider the time it takes to flow enough air through the vac line to bring pressure up in the diaphram chamber, and the time it takes to pressurize the line itself, etc. It becomes a time delay thing. Like I said before, in a static system they would equalize and be the same, but things change too fast in real life. I like to use a large inner diameter 1/4 NPT-1/4" hose barb fitting (off myu BJs manifold) to a 1/4 high pressure fuel line hose (nylon reinforced, doesn't flex under boost, reduces the time it takes to pressurize it), to a 1/4" barb on the Tial BOV. The better the flow path to the diaphram the more you can reduce the loading effect.

I also dont understand the "pull type" / "push type" debate. Does the SSQV really funcion better than the push types?

I've never run a SSQV, but maybe this story relates. The stock EVO BOV leaks pretty good even at low pressures. At 25 psi I'm sure it's significant. I'm running the maximum boost the stock turbo/wg will allow, so I need to make sure all of that airflow makes it through the motor ;) I install the BOV backwards at the track. In this configuration (pull type I guess?) any pressure in the pipe forces the valve closed. THe higher the boost, the more the pressure is holding it closed. THe downside is that it is not sprung correctly (like a perrin or ssqv should be) and it wont open easily or quickly. At the track I don't lift on shifts, so it only affects things when I lift after the traps. I boost leak tested this stock BOV backwards and it does not leak at all.

So now the number of forces and in which directions they work has changed. Now you have boost in the diaphram, spring pressure, and boost in the UICP all pushing it closed. :) The trick is to use a ligher spring (very light I would imagine) so that vacuum on the diaphram is strong enough to pull it open quickly. These valves are usually pretty tunable, with different springs available, adjustable pretension, adjustable throw, etc. I have no personal experience with them however. Based on my success with the backwards stock BOV, I would upgrade to a Perrin if I was going to, if for nothing else just to try it and learn something from the experience.

"[1g bov's] start blowing open around 18 psi, but they have no surge at all and blow off easily."

That is because of the aforementioned fast release port that is built in. And blowing open at 18 psi or whatever is a result of the same action.

A gus modded BOV really is best. And you can gus mod a Type S since it has the second port available. When doing this to a 1g valve we are really just doing the same thing. Intercepting that lower port and making it accessible to us.

Oh, then someone said this:

"I am fortunate to live literally around the corner from Rhys Millen Motorsports. After a long discussion with the techs, the conclusion was NO advantage to a BOV. They routinely race rally-prepped cars with 400+ hp and have yet to need a BOV. A good turbo upgrade and free-flowing air are the biggest contributors to performance. If you want to hear that "whoosh" noise, play Gran Turismo...."

What is that about?


I have no idea what that guy is trying to say. No BOV at all? No aftermarket BOV? I would say he is wrong on both accounts, regardless of what RMM told him. Not to mention that 400 hp is a bad example considering how incredibly easy it is to reach that level on these cars, and the EVOs especially. I'm over 400 crank HP with just a filter, exhaust, cams, and DSMlink :icon16: I guess it's OK for me to upgrade my BOV now :rolleyes:

Ok so I just put my second 1g bov on my car and it rings just like the old one, wtf. It doesn't do it as bad but this one seems to have two different tones like a flute or something. If this has happened on both of mine it must be happening to everyone else so why isn't anyone talking about it? Anyone know a fix?

I also have a massive boost leak (couldn't build more than 5 psi with the air tank) on the back of the bov gasket. I tried to fix it with Permatex Ultra Copper RTV but I gotta try again since I didn't use enough and air is still whooshing out the back. Oh, I also tried pushing on the valve to see how hard it was to move it and all I gotta say is it's amazing that thing can move that fast.

Btw, thanks again Kevin. :)

I have a feeling the ringing has more to do with the rest of the car, IC pipes, intake pipe, etc. I had it on the 2g in its latest configuration when I sold it, but never had it before, with the same BOV IIRC.

All hail Kevin. Honestly, I don't know what the hell I just read, but I think you know your shit...

I don't really know much, I just try to confuse everyone with strange words and acronyms. It's been working so far :icon16:

I have to say I am impressed with kevins explanation and also happy to see that kevin has stayed aboard to help out. I have somewhat read about the "gus" mod and decided to pass it up for now.....
If kevins explanation wasn't "good enough" for some to understand... I would suggest doing a google search for more information. I did it quite a while ago and at the time found LOTS of information on the internal dynamics of how a BOV works.
Good write up KEV.. kudos to you.

I would suggest doing a google search for more information. I did it quite a while ago and at the time found LOTS of information on the internal dynamics of how a BOV works.
Good write up KEV.. kudos to you.

Damnit, I did a google search before I started this thread and couldn't find hardly anything useful. I was also trying to find some info on stock mr2 bovs since they are supposed to be good. Couldn't find anything on that either.

Btw, the ringing is sooooo annoying and seems to be getting worse! Arrrrgggg! I've tried putting pieces of rubber in between the uicp and other metal to metal contacts but doesn't do anything. I swear it HAS to be the bov.

Just wanted to say it's not just me that has this problem with the 1g bov ringing. I've read at least 5 threads where someone describes exactly what's happening to me. Like this one from DSMTalk: http://www.dsmtalk.com/forums/showthread.php?t=40545&highlight=bov+ringing

"On my 2g with the 1gBOV in it at precisely 2100rpm it has the annoying balance of air going through it so it makes a LOUD ringing sound almost as if my brakes are going.. "

I don't know how people deal with this annoying sound. It has almost made me want to shell out the extra $200 for a type s. And I've pressure tested the intake to 12 psi so I don't think it's a leak.

mine does it. i have a gus modded 1g bov. im venting it right now because i have a vpc and can lol.

when i slow down it "coughs" then right as it drops to idle i get a little whistle noise from it. it will also whistle if i hold it at just the wrong spot. i havent figured out how to stop it yet. eventually i want to get a hks ssqv.

the downside of gus modding is that if you accelarate hard and build boost then suddenly let off. it jerks right before it releases. if your shifting you dont notice but if your cruising right on the edge of boost its a pain in the ass

"On my 2g with the 1gBOV in it at precisely 2100rpm it has the annoying balance of air going through it so it makes a LOUD ringing sound almost as if my brakes are going.. "

My type s does this, although I wouldn't describe it as "LOUD", it is still noticeable.

My type s does this, although I wouldn't describe it as "LOUD", it is still noticeable.
Wow really, I've never heard of the type s making the sound. Is it a ringing sound *almost* like brakes squeeling?

On the 1g bov I'm using now the sound is not as loud but on the old one I'd say you could clearly hear it from 30 ft or so. I am somewhat considering a Greddy or HKS knockoff since I've read numerous posts from people using them that they perform exactly the same as the real ones, especially the HKS. Someone actually took their Type s knockoff apart in this thread: http://www.dsmtuners.com/forums/showthread.php?t=200908&page=2

Wow really, I've never heard of the type s making the sound. Is it a ringing sound *almost* like brakes squeeling?

On the 1g bov I'm using now the sound is not as loud but on the old one I'd say you could clearly hear it from 30 ft or so. I am somewhat considering a Greddy or HKS knockoff since I've read numerous posts from people using them that they perform exactly the same as the real ones, especially the HKS. Someone actually took their Type s knockoff apart in this thread: http://www.dsmtuners.com/forums/showthread.php?t=200908&page=2

http://www.clipsekid99.com/videos/bov2.divx here is a video of it kinda. You can hear it like right at the last second. Turn your volume up to hear it better.