high altitude B.O.V

[pagosa dsm]

I live at 7500 feet. I don't think my B.O.V is opening up fully.I have a factory 92 B.O.V.I checked my valve,it started opening at 53.3 kPa or 17" of vacuum .fully opened at 20" of vacuum. I don't get 20' of vacuum.Do they make an adjustable B.O.V or one for high altitude?

 

[cruisintalonawd]

Huh?????????do you mean in. HG good way to tell is plug the rec. hose and see if you hear it then plug it pack in

 

[brute]

At high altitudes, the idle vacuum is lower than at sea level. I live at high altitude along with you, and I pull about 13 inHg at idle. The spring inside your valve may be too hard and the engine isn't pulling enough vacuum to open it. However, since you have a stock BOV, we're going to need to investigate further. Is it crushed or modified in any way?

For what it's worth, I run an HKS SSQV and couldn't be happier. Doesn't surge and doesn't leak.

 

[pagosa dsm]

At high altitudes, the idle vacuum is lower than at sea level. I live at high altitude along with you, and I pull about 13 inHg at idle. The spring inside your valve may be too hard and the engine isn't pulling enough vacuum to open it. However, since you have a stock BOV, we're going to need to investigate further. Is it crushed or modified in any way?

For what it's worth, I run an HKS SSQV and couldn't be happier. Doesn't surge and doesn't leak.

Thanks for you reply,the B.O.V is stock and not crushed.I will check out theHKS SSQV.

 

[brute]

Thanks for you reply,the B.O.V is stock and not crushed.I will check out theHKS SSQV.

You'll need to get the recirculation fitting, which is sold separately. It's a very high quality valve, and you won't ever need to upgrade!

 

[tkelly27]

The 1g has 3 features that cause it to open. First is the vacuum, second is the boost pressure acting on the bottom of the valve, and the third is a port that allows the boost pressure to push under the diaphragm. Static opening conditions don't necessitate that the valve will not open under the condition of boost in the charge piping and vacuum from the engine. It doesn't need to be open while idling, and it will shut again the instant you blip the throttle.

They sold 1g DSMs in the rocky mountain areas and they all worked, no reason yours shouldn't : D

 

[ApexVIII]

i live in CA at abput 20ft above sea lvl, when i took my evo up to go snowboarding at like 5000ft i started loosing vaccume and gettin compressure surge. my vac normally was like 18-19, and above 5000 it was like 15 and it started getting it.

 

[Gregory]

Your BOV should function fine at theoretically any altitude. No matter the density of air you see where you live, when you close the throttle plate, the difference in pressure between the intercooler piping and the intake manifold will want to pull the valve open had you been making any airflow at all. That little hose that runs to your BOV is that vacuum source and is sort of an important part. When your throttle is open, is pushes down on the valve with equal PSI that is being pushed up on it (but note that they see different surface areas, so the force acting on the valve is still not quite 1:1), and when you close the throttle, you're now applying more PSI under the valve than above it, so it wants to naturally open the valve so the pressure can become equal. These principles should apply no matter your altitude. As stated above, there are also other things that open the valve, but as far as air density goes, that's it.

 

[brute]

Your BOV should function fine at theoretically any altitude. No matter the density of air you see where you live, when you close the throttle plate, the difference in pressure between the intercooler piping and the intake manifold will want to pull the valve open had you been making any airflow at all. That little hose that runs to your BOV is that vacuum source and is sort of an important part. When your throttle is open, is pushes down on the valve with equal PSI that is being pushed up on it (but note that they see different surface areas, so the force acting on the valve is still not quite 1:1), and when you close the throttle, you’re now applying more PSI under the valve than above it, so it wants to naturally open the valve so the pressure can become equal. These principles should apply no matter your altitude. As stated above, there are also other things that open the valve, but as far as air density goes, that’s it.

That is correct, however, there is a huge variable involved: the spring. Depending on the pressure differential and spring constant, you can get the valve to never open at all. Say you only boost up to <5 psi maybe on like highway driving. You live at 5000-6000ft (atmospheric pressure ~12 psi). Your car's resulting vacuum may not be enough to over come the small pressure differential or even the spring constant.

This is precisely the reason that there are trade offs when you start running tons of boost. You don't want the valve to leak under 40+ psi, so you pack the thing with springs, but this is at the cost of engine vacuum no longer being able to pull it open until there's a pressure differential at maybe like 10psi. So anything <10psi, you're going to be surging like a madman.

This is just a crude, theoretical conversation, though

 

[Gregory]

That is correct, however, there is a huge variable involved: the spring. Depending on the pressure differential and spring constant, you can get the valve to never open at all. Say you only boost up to <5 psi maybe on like highway driving. You live at 5000-6000ft (atmospheric pressure ~12 psi). Your car's resulting vacuum may not be enough to over come the small pressure differential or even the spring constant.

This is precisely the reason that there are trade offs when you start running tons of boost. You don't want the valve to leak under 40+ psi, so you pack the thing with springs, but this is at the cost of engine vacuum no longer being able to pull it open until there's a pressure differential at maybe like 10psi. So anything <10psi, you're going to be surging like a madman.

This is just a crude, theoretical conversation, though

True true, I was alluding to the spring when I mentioned the above posts. You have an excellent point, but my thinking is if he is boosting under 5psi, there is normally not a need for opening the BOV. That kind of air density isen't going to cause you any damaging compression surge. If he was boosting a bunch and it was never opening, obviously there's a problem, but with a stock setup and a stock BOV (with a stock spring), there should be no probem. I think they knew this when Mitsubishi engineered the cars. What you said about running tons of boost, I know what you mean.

edit: maybe this isen't the case for him cause I thought he was stock for some reason. Do we know how much boost he's running?

 

[brute]

True true, I was alluding to the spring when I mentioned the above posts. You have an excellent point, but my thinking is if he is boosting under 5psi, there is normally not a need for opening the BOV. That kind of air density isen't going to cause you any damaging compression surge. If he was boosting a bunch and it was never opening, obviously there's a problem, but with a stock setup and a stock BOV (with a stock spring), there should be no probem. I think they knew this when Mitsubishi engineered the cars. What you said about running tons of boost, I know what you mean.

edit: maybe this isen't the case for him cause I thought he was stock for some reason. Do we know how much boost he's running?

We're saying the same thing just in a different way

pagosa dsm, I'd suggest taking off your BOV and testing it. Put some pressure on it and see about the actuation. See if it opens all the way and all that good stuff. If it's still no good, you may try taking it apart and look at the diaphragm, piston, and nipple passage ways to see if anything's awry.

Keep us updated!

 

[pagosa dsm]

I have tested the BOV with a vacuum pump.The results are it start to open at 17" and fully opens at 20" of vacuum.That is the factory specs. Some body asked how much boost,I run 19-20#s with an evo 3.

 

[ktmrider]

Hey Pagosa, another ABQ member like Brute.
I have a boost only gauge in the GVR4 at the moment but can hear the BOV hissing when I let off the go pedal. It's not a ton but definitely audible. Same with the Talon but even louder due to the fresher motor likely pulling more vac.
My WRX used to pull about 16" at idle but under deceleration would grab 20" and open the BOV. I could hear it close the moment I got back on the throttle.
I took the WRX to Ouray last summer ( 7000+ ) and noticed about 13" at idle and 17" decel. Over the passes I did not hear the BOV engage.
Like suggested get a super sequential ( SSQV ) adjustable valve. They hold the diaphram closed at the higher boost levels you run.