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Discussion Starter #1
Anyone catch the Monte Carlo WRC last night? Awesome!! Anyway,
as I'm sure most of you already know, the cars are always making this kewl little chirping noise. I always assumed it had something to do with a belt, a suspension component, or even possibly the turbo.

As I was watching a stage last night, the announcer said something like "yeah..you can hear him decelerating (his words) as the blow off valve chirps...".

So this lead me to the conclusion that the strangely alluring chirping noise was the BOV letting off excess pressure when the throttle was released. I thought this was odd as all aftermarket BOV's I've heard make a prolonged sound like a woosh or a whistle. Now to the heart of the post:

Is that chirping noise on the WRC cars actually the BOV and if so, why does it make that type of noise? Extremely reactive solenoids? A vent muffler of some sort?

Would love to have the STI (once acquired) make the same announcement coming into a 25MPH corner at about 80....chirping and downshifting and drifting and left foot breaking and e-brake sliding and hooking up with all 4 biting leaving nothing but a bit of tire smoke and a 2.5 rasp in my wake (and maybe the echos of cheering air horns) !!!!!!!!!! :eek:

ok...got carried away there. (I know you know the feeling!!) Seriously, is the chirping the BOV and can we get a set up like that?

Cheers,
Scott
 

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Yes, that is the blow off valve...it's sounds more like a squeeky suspension component, but that's it.

Not real sure why they sound that way, other than that they really don't care when they sound like, they just want that pressure gone, and now! Compared to most blow of valves, you'll notice that they usually only 'sound' twice during a downshift, vs. the 3-4 a normal blow off valve would give.

I don't know the specs of the thing, but I'd be it's a very fact actuating BOV, the reason for the sound.
 

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a modded civic was driving around campus yesterday and gave that chirping BOV sound everytime they got off the gas. i would normally assume it was a true BOV, but it might be "riced"; there's a speaker under the hood that chirps when you get off the gas. now wouldn't that be hilarious.
 

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Several cars at my alma mater had that device. :lol: :lol: What a bunch of tools...

But, GOOD BOV's make more of the chirping sound, while the ones that really don't help anything performance wise make the whooosh sound.

How about an anti-lag system? Now that would be some fun for the cars in back of you. :) :evil:
 

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Someone else probably could give a better explaination, but here goes my best:

An Anti-Lag system keeps the turbo spooled up and ready to provide instant boost when you shift, take your foot off the gas, etc. It is a igniter element in the exhaust that lights the excess gas in your exhaust, causing backpressure, which causes the turbo to remain spooled for a time.

It produces not only a BIG backfire like sound (only louder), and FLAMES out of the tailpipe that can reach a few feet in length. :D:D

It'd be cool to "flash" a car right before you murder them in a race. :evil: :)
 

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JJ said:
It produces not only a BIG backfire like sound (only louder), and FLAMES out of the tailpipe that can reach a few feet in length. :D:D
wicked cool. where can i get one? on the other hand, i'd probably be liable for burning paint of the car behind me.
 

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JJ said:
lights the excess gas in your exhaust, causing backpressure, which causes the turbo to remain spooled for a time.
I haven't heard of these things before, but that doesn't quite make sense. If it lights off the gas that's still in the exhaust, it would cause the fire/explosion, lowering the pressure which would maintain the pressure differential across the turbo, which is what spins the turbo in the first place.

Any links to these systems? I'd guess you couldn't run it on a typical exhaust system as well (cat/muffler in place).
 

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Discussion Starter #11
Ok...so we've established that the "chirping" noise is the BOV, that it is probably a fast reacting solenoid type, and that it offers better performance over the whooshing/whistling types (and of course over those awesome speaker BOV's :wink: ).

Next question...does it relieve to atmosphere or internaly (as normal)?

Final question...same as before...anyone know where we can pick one up?


Thanks
Scott
 

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I know how the general turbo systems work, but I haven't a clue how makes a good BOV or what different types there are.

As for the relief flow of the BOV, being a race system, I'd bet it's released to atmosphere. I believe emissions are the reason that most BOV or other boost relieving systems send the flow back into the intake track, but I'd think that would create flow issues in the intake where that fast-moving flow would be brought back into the main intake track. Just a guess.....
 

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Discussion Starter #13
Thanks Rob and JJ :lol: . Much appreciated. I'm still on the hunt for the WRC BOV though. Maybe Prosports supplies 'em. Heading to the UP in MI soon, so maybe I'll actually stop in and see whats up.

Scott
 

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Recirculation BOVs are used when you have a MAF sensor, which I'm pretty sure most cars use. So, they are stock on most FI cars.

The way I read it was, the MAF counts air which, if not recirculated, gets lost if you're using an Atmospheric BOV. So, the EMU gets a reading for more air than is actually making it into the combustion chambers. So, in theory you end up running rich, which you could also in theory tune for. Therefore it has been said that atmospheric BOVs have no redeeming qualities unless you switch to a pressure sensor system. Of course you could just like listening to the sound.

There's always big debate on the whole Recirculating/Atmospheric BOV topic on one of the main DSM forums. I think they ended up just making it a "Sticky".

http://www.dsmtalk.com/forums/showthread.php?s=13e2ff91e3c75784815e1689a24ed21c&threadid=30252
 

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Yeah, I was reading all that MAFS difficulty stuff too. I'm trying to figure this out though.....

You WRX guys, get in here and answer this. The stock 'bypass' valve...where does that bypass to? It's back in the intake track, right? Somewhere after the filter and somewhere before the turbo, right?

My ? is....how does the stock MAFS know how much is bypassed back away from the engine? If the stock setup avoids this rich condition, it must know exactly how much is bypassed, is that right?

All this is getting confusing and I'm having a hard time finding answers.
 

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Forget Portland, OR

Well, I've talked with a few people about this and I guess it makes a little more sense. If you think of the bypass as doing nothing more than eliminating the pressure difference across the turbine, it makes more sense. The air is all still there, and so on.

The thing that was getting me though was this.

Ok, consider the flow of air through the intake-turbo-TB a constant flow, kinda like water. At a constant flow, the MAFS knows how much is flowing through it at the time and how much the engine should be suspecting. So say the air is flowing at a unit of 5 per second. So the entire line looks like this....

5--------------5-----------------5--------------------5-------------------5

Nice and smooth. Now, when the bypass is opened, some of that air right before the TB is passed back to the begining of the flow, right? But, supposedly, the engine still knows how much fuel to add. But with that bypass moving that air back to the beginning of the line, wouldn't the engine still NOT be getting the air it thinks it is? Kinda like this?

5-------------8----------------5--------------------5--------------------2

I suppose if you think about the air flow moving fast enough that this differential isn't there as bad as shown.

I dunno....unless someone can explain this differently, I'm starting to wonder if this whole BOV-running rich thing isn't a bunch of bunk.

Does this make sense to anyone?
 

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Oh wait....the lightbulb just went on....wow.

If anyone cares to hear it....lemme know. Feeling a little on the dumb side here. :)
 

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Here's a good explanation I found that says it pretty well.....

shabby, the ECU pumps fuel according to how much air is seen by the MAFS, there's no way around that. Venting off the air means you will be pumping more fuel than you have air for. I also don't think you understand how the air actually flows. In a normally aspirated car, umm... lets say that you are revving the engine. Then you take your foot off the gas which closes the air valve quite a bit - controlling how much air enters the cylinders this IMMEDIATELY reduces the flow of air into the engine AND the flow of air past the MAFS. The air flow is stalled immediately, ALL the way back to the MAFS. Yes, there is a little bit of compression, but you'll be surprised how little. The ECU also helps in this area.

Now in the turbo engine the same is true as long as you vent the air back into the air intake at a point past the MAFS (so that the MAFS does not read the same air twice or more). When the BOV is activated, and the turbo is still spooled up, the compressor will continue to move air, but at this point it is re-circulating through the mid portion of the car's intake (Or to be competely accurate the air is continuously circulated from the BOV through the return, through the compressor, through the intercooler and back again to the BOV.) The upper portion being the point before the MAFS. And the lower which is from the BOV to the cylinders. The middle part is then subsequently the part between the BOV and the MAFS.
 
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