I just want to share my recent experience with BOV.

I upgraded my a-trim (swapped volute housing and impeller) to an s-trim recently. I'm also running a small 3.33 pully up top.So we're talking lots of boost.

I got a BOV from a 1g DSM from Inwo, a moderator in the street racing board. I welded up a flange on the discharge tube, and ran the bov to atmosphere. Lemme tell you - it helps driveability big time!..

During idle, lef off throttle, and cruise it vents. During hard acceleration, and boost of course is closes right up.

Blower is happy. I'm happy..

-- Joe

 

Sweet! Got any pics?

 

http://members.cisdi.com/~anesthes/p...s/bird-eng.jpg

-- Joe

 

I'm currently using a 1G DSM Eclipse BOV on my Avenger right now. Did you have yours crushed? If not, CRUSH IT! When they're crushed, they hold upwards of 20-25psi of boost. I'm running about 13psi right now (need to redo my fuel system to up the boost) and it holds strong.

 

i was told 1st Gen DSM BOVs were on the small side and that if you were pushing alot of air, it wouldnt be able to blow enough off....

any truth to that? or was it just for extreme apps? or does it not matter because its a supercharger, not a turbo, and the charger spins down with the engine quickly enough not to be a issue?

 

I hear a lot of good things about the Tial BOV's.

 

The supercharger will spin down with the engine, you just want the excess air to get out of the discharge tube.

The 1g dsm bov is suposedly a nice peice.

I didnt have it crushed. I have the dejon tool kit which allows 20-25psi.

-- Joe

 

what does having it crushed mean? is it a method of applying more preload to the BOV so it doesnt release until a higher pressure is reached?

 

Basically, yes. You cush the top half of the enclosure (above the diaphram with the spring in it) in increments of maybe .050 - .100" until you get the desired spring pressure.

There are better ways of accomplishing this however, one of which involves separating the two halves, putting shims behind the spring, and closing it all back up with a 2" v-band type clamp.

http://www.dsmtuners.com/forums/show...threadid=97971

I looked into this, but i would rather have it blowoff sooner than later, since i wont have more than 12-14 psi boost MAX. I did a test on mine and found that it starts to leak significantly around 15psi and cracking pressure is around 20 psi (stock).

 

There is absolutley NO reson to this. It is actually stupid to do it.

You want the BOV to open easy, and you need very little spring pressure to keep it closed at ANY boost level if it is installed correctly.

You have a vacuum port on the BOV and that must be connected to a vacuum port after the throttle.

With the throttle closed the BOV should be held open by the engine vacuum.

During WOT you will have the same pressure on both sides of the spring and the spring pressure will keep the valve closed at ANY boost level.

 

Your saying that the pressure delivered thru the vacuum line is equal to the pressure being applied to the BOV?

I.. just don't see it. The pressure being applied to the valve side of the BOV has a greater area than the diaphram side of the BOV.

???? BW

 

If that is true then the BOV is of a bad design.

The one I have has a larger area on on 'vacuum' side than on the valve side. It will close harder at higher boost. It is also a dual piston type. The small piston acts as a check valve so air will not enter thru the BOV.

Here are pictures of it:

 

thats a pretty nice design. i like the idea of having the secondary spring to keep the valve closed even at high engine boost, but still have the ability to release charge air.

 

This is another design with a 2" connection.

It was a single piston BOV ( top row ) and it worked great.

I modified it into a dual piston and it works even better.

http://jobyteknik.homeip.net/fredrik...04-04-03_Dump/

 

Huh, I'm not sure that I get the point of the second piston/spring.

As far as the rest of this conversation goes, having a fitting on the back side of the diaphragm and just enough spring to make it consistent and sit against the seat with no pressure differential, and then just letting the boost pressure in the manifold do the rest is pretty typical. That's the basic design of the bosch valves used OEM on the porsches, audis and saabs (as well as the one supplied with some vortec kits). The problem isn't really overpowering the spring, but big pressure differential slamming things around in there too much messing up how things seat or ripping the diaphragm.

 

During idle the BOV will stay open and the engine can get unfilterd air thru the BOV.

There are four solutions that I know of.

1) Put an air filter on the BOV

2) Connect the vent holes to the piping between the air filter and the turbo. This is very common on stock turbo cars, and needed if you use a MAF sensor.

3) Use a stronger spring to keep the BOV closed at idle. This is not a goos solution because it will not vent as good when it should.

4) Use a second piston as a check valve. This should have a very weak spring to open easy. This is how I modofied the second one.
The fist one works like that from the factory.

 

Joe,

The way you describe the operation sounds exactly like my surge valves. Here's my interpretation:

Surge Valve
Open under vacuum.
Closed under boost.

Blowoff Valve
Closed under vacuum.
Open only when a pre-set boost value is attained, thereby relieving unwanted pressure.

Am I wrong?

Willie

 

whats the pt# of that bov

thanks

 

During idle mine blows air out. How would it suck in?

[quote]
The way you describe the operation sounds exactly like my surge valves. Here's my interpretation:
[/qupte]

Exactly! But the DSM guys call it a BOV or a "compressor bypass valve" In any event, vacuum at idle keeps it open, on shifts the vac dives and it opens, and under boost it's closed cuz no vac. The spring keeps it shut, and the boost in the line I imagine helps as well.

Well the pressure is the same right, 15psi or whatever but the CFM won't be. hehe.


-- Joe

 

A centrifugal supercharger allways blows more air than the engine needs, so then it is not a problem.

With a turbo it is different. Then then engine could use more air then the turbo blows berfore the turbo starts to spool.

 

Kewlness.

-- Joe

 

I've never seen one suck air in through a blowoff/bypass, but I suppose it's possible. If that's happening put a check valve in the vacuum line to the back of the diaphragm and a small bleed. That will only allow that side of the diaphragm to see pressure, no vacuum so it can't open at high vacuum situations unless your blower is moving too much air.

As far as all this goes, on my brother's car we had assorted problems with diaphragm actuated blow offs and finally made our own, using a butterfly and an aluminum housing for which he rigged a cable linkage to the throttle… throttle open, butterfly closed. Throttle closed, butterfly open. Simple and effective.

 

I think a piston type is better than one with a diaphragm. A diaphragm can break, but a piston will not.

The dual piston works great and is simple. When we get the plenum back on ( changing injectors ) I can make a movie that shows it in operation.

I don't see how the checkvalve / bleed thing would work. You want it to open fast when you get vacuum and then close when the boost pressure is released.

 

cool

 

I always just used a little fake K&N from the "r!ce" section at the auto parts store on the end of the bov

 

Hmm... I've been using 2 of the 1g DSM BOV's on the Bu. Even with both, the CFM of the blowers at idle exceeds the CFM capability thru the BOV's. How I know is the blowers are much quieter when the dischage tubes are disconected, than with them connected, and passing air past the BOV's...

I think you just gave me a use for my LS1 type TB...

Oh.. No I don't have any numbers on Caddy's.. BW

 

That sounds like the problem that my brother's car was having… he was trying the bosch one that comes with the vortecs and it was just doing all sorts of evil stuff to the charge plumbing.

His butterfly started as the stock T-bird bypass, was cut out of the housing and tigged to the charge tube and got a new hand fit butterfly plate (the stock one is missing a good size chunk, I'm guessing to bleed off a little boost).

 

hey saturn5, drop me an email when you have a second... I lost your's and have a question for you off list. Thanks

 

You've got mail.. BW.

 

I made a movie today where you see the two pistons working.

Without vacuum both are closed.
Without boost the second one is allways closed.

Movie: ( right click and save as ) 5.5Mb
http://jobyteknik.homeip.net/fredrik...1/MOV02977.MPG

And pictures of the parts:
http://jobyteknik.homeip.net/fredrik...004-04-03_Dump