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Old 10-31-2007, 11:47 PM   #1
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Default A question about my odd BOV

As you guys rember, my turbo has a BOV on it. Now I think the spring in it is too stiff, and heres why:

When I am flooring it and over 6k RPM, then I let off, it works just like a blow off valve should

Anything less than flooring it and over 6k rpm, I get compressor surge.

So am I correct in assumeing its the spring? How do you think I should go about fixing this? Does it need to be fixed (aka is compressor surge ok at lower boost levels, as long as the BOV works at over 5 psi of boost?)


Rember, the turbo with the BOV is off a merc 2.2L diesel engine.
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Old 10-31-2007, 11:49 PM   #2
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I would take the spring out and get some measurements on it. Then hunt mcmaster for a similar spring. I bet you can source one pretty easily. There isn't really an easy adjustment you can do to the spring to make it lighter.

Also, where are you getting your BOV signal from? Should be the intake manifold obviously, where on the intake manifold? You might just need to install a bigger 1/8" NPT fitting and run a larger 3/8" vac line to it.
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Old 10-31-2007, 11:51 PM   #3
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do you get compressor surge or simple bov flutter?
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Old 10-31-2007, 11:56 PM   #4
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The turbo has a vac/boost feed nipple (atleast 3/8 inch size) on the compressor houseing. I have a line comeing from that, splitting into the wastegate, BOV, and boost gauge/bipes. I am using the right size line for the connector on the BOV, so I should be good.





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do you get compressor surge or simple bov flutter?
I think its surge, but is there a way to tell the difference? When I let off, the boost gauge does go up and down alot (fluctuate) when I get the sound (hard to explain, its like the gauge spazes while it reduces in boost). The turbo makes a chugging ish like sound. Ill take a video tommorow.
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Old 10-31-2007, 11:57 PM   #5
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cut a coil off the spring and try again.

I ended up cutting probably 5 coils off my BOV's spring, and then adding a second, short and stiff spring inside of it. Works pretty good.
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Old 10-31-2007, 11:58 PM   #6
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cut a coil off the spring and try again.

I ended up cutting probably 5 coils off my BOV's spring, and then adding a second, short and stiff spring inside of it. Works pretty good.

Ill try it tommorow.
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Old 11-01-2007, 05:59 PM   #7
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I took 2 coils off, works better but im still getting surge. Here is a vid so you guys can decide.. I tryed my best when takeing it lol.

http://videos.streetfire.net/video/0...d90114218f.htm
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Old 11-01-2007, 06:02 PM   #8
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I just have crappy laptop speakers but i can't hear anything but engine noise. I don't hear any blow off or surge.
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Old 11-01-2007, 06:06 PM   #9
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Originally Posted by cjernigan View Post
I just have crappy laptop speakers but i can't hear anything but engine noise. I don't hear any blow off or surge.

It is hard to hear in the video, maybe I should try with the windows up? You can see the boost gauge fluctuate when I let off.
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Old 11-01-2007, 06:11 PM   #10
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Couldn't hear it at all, and my computer audio system consists of a surround receiver and a pretty decent sub/sat speaker package.

I wouldn't be concerned with surge from 5 psi hurting the turbo.
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Old 11-01-2007, 06:14 PM   #11
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I wouldn't be concerned with surge from 5 psi hurting the turbo.
I was wondering if surge is ok at below 5 psi. If it is, im just not going to mess with it. At what pressure does surge really become a problem?
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Old 11-01-2007, 07:54 PM   #12
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Try using a dedicated vac line for your BOV rather than tee'd off other stuff.

Actually, thinking about it, the vac source for you BOV should be from the intake manifold AFTER the throttle body not off the turbo. Think about it, during boost with the throttle plate open, both side of the BOV diaphram are pressurized so the spring keeps the BOV closed. When you let off the gas, the throttle plate closes and you have vacuum on the IM vac lines (which should be attached to your BOV) and pressure between the turbo and IM acting on the other side of the BOV. So you have vac on one side of the diaphram and pressure on the other so it opens.
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Old 11-01-2007, 10:21 PM   #13
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Brg is correct, that's why i asked where you had the signal coming from earlier in the thread. You won't see hardly any vacuum at all when you let off the throttle. You want line coming form the intake manifold to get maximum vacuum to snap your BOV soon as you let off the throttle. Only your wastegate should receive signal from the compressor. If you hook your boost gauge up to your intake manifold you'll see exactly how much boost you're seeing after the loss from the intercooler. Well actually you'll see how much boost you're running relative to how accurate your gauge is.
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Old 11-01-2007, 10:27 PM   #14
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Quote:
Originally Posted by cardriverx View Post
The turbo has a vac/boost feed nipple (atleast 3/8 inch size) on the compressor houseing. I have a line comeing from that, splitting into the wastegate, BOV, and boost gauge/bipes. I am using the right size line for the connector on the BOV, so I should be good.
Oh snapz, I didn't even see that. Listen to Tom and Chad. You need to source your vac signal from the IM.
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Old 11-01-2007, 10:31 PM   #15
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I think we need to slow down and start reading more closely, 2nd thing i missed like that this week.
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Old 11-01-2007, 10:50 PM   #16
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I was wondering why nobody noticed it as I was going through it just now. Get your BOV and Boost/Vac gauge signal from the manifold (after the throttle plate of course) and I bet it will work like a champ.
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Old 11-01-2007, 10:56 PM   #17
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Cause you know that merc BOV can't have that heavy of a spring on it. Pretty sure its a similar turbo to what is on my buddies 300D turbo diesel.
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Old 11-01-2007, 11:36 PM   #18
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lol, thanks a ton guys. Now, would the two nipples on the throttle body be considered after the throttle plate? If not, where else should I get the signal from?
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Old 11-02-2007, 01:00 AM   #19
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ya, those work, or you can tee from the fpr, or you can drill and tap where you want to.
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Old 11-02-2007, 01:13 AM   #20
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Quote:
Originally Posted by cardriverx View Post
lol, thanks a ton guys. Now, would the two nipples on the throttle body be considered after the throttle plate? If not, where else should I get the signal from?
Yes they are after the TB, theres also a cap on another port on the back of the intake manifold
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