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      09-20-2010, 08:24 AM   #45
bradleyland
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Quote:
Originally Posted by RPM90 View Post
Just for clarity sake, because things get promoted in these forums as if gospel.

I'm sure you guys are hearing what you say you hear.
However, you are not hearing a "BOV". I know some of you know this, but it seems some don't get this.

A real BOV is night and day difference in sound and volume compared to a recirc DV.
With a DV the pressurized air is not being "blown off", it is recirculated, or returned, into the intake path. A "blow off" does indeed blow off/out the pressurized air to atmosphere. That's why it's so much louder, and cooler.

Given that the N55 has not throttle plate, as it uses valvetronic intake control, it really is a unique system. With a standard throttle plate, once the plate is closed, the pressurized air leaves the BOV or DV, so that there is no more pressurized air going to the intake manifold. But, with valvetronic, the air intake to the combustion chamber is controlled by the action of the intake valves. So, imagine them as individual "throttle plates". This probably also adds to why the N55 can should hold boost better in between shifts, even with a manual trans.

I need to look into how this N55 engine works, more closely.
I'd also think that the DV is located in a different area compared to the N54. The location of the N55's DV could also lend to hearing it better/louder.
I'm not sure anyone is claiming they hear a "BOV".

However, based on what I hear in my car every day, and the input from others here, the operation of the DV on the N55 is significantly more intrusive than the N54. If I accelerate hard out of a signal light (like if I need to get over a couple of lanes), I can hear it inside the cabin when the radio is off. With the windows down, it's a clearly audible 'pksssssss' sound. Very different than the chatter of some BOV designs, but definitely the sound of air being pushed hard through an orifice.

Sometimes I like it, sometimes I wish it didn't happen. I recently picked a colleague up from the airport in Tampa and he heard it go off as I accelerated on an on-ramp. His immediate impression was that something just "blew out". I told him it was just the DV and he looked at me like I had three heads.
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      09-20-2010, 09:06 AM   #46
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Quote:
Originally Posted by Jeef Beef View Post
Yep, my DVs are freakin LOUD as with BMS DCIs. It's true that in stock form there was no noise whatsoever, but with the intakes, it does the full 'pssssstttttttttt-teeeeeuuuuuchhhhh' I love it when I drive through my uni on part throttle in 2nd gear, and then abruptly let off. Everyone turns around and expects an Evo/WRX, and instead they have this puzzled expression on their face as a bimmer drives past.
lol I do the same thing. I cruise around never shifting into third and when I lift for a light all you hear is turbo wine a small psssssssst I should get a BOV
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      09-21-2010, 10:37 AM   #47
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if u really want to hear the blow off on the N54 get the DCI , thats what i have and u dont even have to push the car that hard to hear the sexy sounds ... I havc the steps too and after the JB3 is in with the increase boost it gets lourder on every gear !! love it and never going back to stock... lol
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      10-01-2010, 03:20 PM   #48
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so does anyone actually know WHERE the DV on the N55 is located?
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      10-01-2010, 10:13 PM   #49
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For the first time today, I actually heard the turbos in my car. It's very, very subtle, but in a parking garage driving next to a wall with the windows down, you can hear them. Sounds like a combination of intake + hiss, and then when you quickly lift off the accelerator, you hear a little whistle.
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      10-02-2010, 12:34 AM   #50
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Quote:
Originally Posted by bradleyland View Post
I'm not sure anyone is claiming they hear a "BOV".

However, based on what I hear in my car every day, and the input from others here, the operation of the DV on the N55 is significantly more intrusive than the N54. If I accelerate hard out of a signal light (like if I need to get over a couple of lanes), I can hear it inside the cabin when the radio is off. With the windows down, it's a clearly audible 'pksssssss' sound. Very different than the chatter of some BOV designs, but definitely the sound of air being pushed hard through an orifice.

Sometimes I like it, sometimes I wish it didn't happen. I recently picked a colleague up from the airport in Tampa and he heard it go off as I accelerated on an on-ramp. His immediate impression was that something just "blew out". I told him it was just the DV and he looked at me like I had three heads.
That's funny.

I've never heard my BOV/DV, it's really quite, very much unlike the atmosphere BOV in my long ago Mits turbo. That one was really cool, quite loud for an OEM.

If you hear an atmosphere type BOV chattering/chuffing sound, that's because it's probably set wrong. The sound is from compressor surge where the BOV is not letting the pressurized air out, and the pressure wave hits back towards the compressor wheel as it chops it.
Some say it will damage a turbo, others say a small amount is fine, but most agree that an excessive amount can cause damage. What is "excessive"? Well, if your turbo goes, then you got there.
It's best to adjust things and make sure you don't have it.

Even faulty diverter BOV's can cause compressor surge, though it's much less likely.
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