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Old 07-22-2003, 09:46 PM   #1
Andursun0013
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Default venting BOV to atmosphere

Why do people do this, is there any reason behind it or is it just easier to do? I'm kinda clueless as to what this does for the car. And when you vent it back into the intake..should it go before or after the air would pass over the MAF...I'm assuming after so the MAF woudldn't read the air twice

Kyle
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Old 07-23-2003, 12:07 AM   #2
trilap5e
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ok... here are a couple of reasons - first off the noise. you know what a bov sounds like right? exactly! blowing it back into the intake would dampen this sound. secondly, some systems do recirculate the boost, but if your blowing off the butterfly valve in the TB is closed (why you blew off in the first place) - so it doesn't make much sense to blow it back into the intake. get me?

there are many reasons - these are just some black and white examples. hope this answers your question.

- Ryan
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Old 07-23-2003, 12:46 AM   #3
Mancini
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Pretty much 2 reasons to return to the intake I can think of. 1. If you have a MAF the air is already metered like you mentioned. 2. Some BOV's open at vacuum to give better throttle response on tip in (by passes the turbo and air gets directly to the TB). So you'll be sucking in dirty air or unmetered air if you tune around the venting on a MAF equipped car. Otherwise, vent to atmosphere and enjoy the sexy pssst noises
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Old 07-23-2003, 09:29 AM   #4
Andursun0013
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cool, thanks guys

Kyle
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Old 07-23-2003, 11:58 AM   #5
BOY
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Other than an overpriced noise maker, an atmospheric BOV serves no useful purpose until you're pushing MAJOR boost. On a MAF equipped car, specifically one that wasn't designed for a turbo, you've already metered the airflow and the ECU is calculating the appropriate amount of fuel... when you vent that air you're pouring too much fuel into the cylinder which can lead to detonation and backfiring into the intake manifold. Another advantage of a diverter valve (recirculating valve, etc) is the airflow is vented back immediately before the compressor which help to keep it spinning and reduces lag.

BOVs, the ultimate rice mod
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Old 07-23-2003, 04:58 PM   #6
Midwayman
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An BOV as opposed to a diverter valve
1) Doesnt put hot air back into the intake tract
2) Allows for a somewhat smoother intake path
3) Is simpler to design (Probably the one of the big reasons you see them on aftermarket kits)
4) Louder. (cool or not, your choice)

If you're replacing a Diverter valve with a BOV and it was working fine before yah its kinda pointless. If you're assembling a MAP based turbo kit, why not use one though.

I think the mainadvantage the BOV's Ive seen vs the diverters Ive seen on RST's is that the Diverters Ive seen have been the cheap nonadjustable ones. A little bit of spring adjustment is always a good thing.
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Old 07-23-2003, 05:12 PM   #7
BOY
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He's running a 98 though, the MAF will

1. Meter the air he's blowing off
2. if the BOV opens at part throttle he'll be running super lean, unmetered air through the BOV into the engine.

If you really want that "hey look at me" sound, get a 50/50 valve that only vents to air at "high" boost (this is adjustable). Either way, until you're pushing BIG boost (20+ psi) its just a party favor.
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Old 07-23-2003, 06:51 PM   #8
Andursun0013
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where do you find a divertor...all i ever see for sale are BOV. Although I don't have a turbo at the moment (or the money for one) I am planning on getting one as soon as I sell my bike (anybody want a 2002 Honda CRF450R....) and I'll need to know where to find this at, I would assume my local shop, slowboyracing.com, will be able to get one for me. While I'm on the subject slowboy does awesome work and are starting to carry more and more subaru stuff.

Kyle

THanks again for all the info
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Old 07-23-2003, 08:45 PM   #9
Midwayman
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well, just because he's running a 98 doesnt mean its MAF. Most PEMS systems are map based.

Alot of the wrx "BOV"'s are really diverter valves. Usually listed as a non-atmoshperic BOV or some such thing.
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Old 07-24-2003, 09:13 AM   #10
BOY
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Default Re: venting BOV to atmosphere

Quote:
Originally posted by Andursun0013
Why do people do this, is there any reason behind it or is it just easier to do? I'm kinda clueless as to what this does for the car. And when you vent it back into the intake..should it go before or after the air would pass over the MAF...I'm assuming after so the MAF woudldn't read the air twice

Kyle
'nuff said? Most PEMS systems use a MAP sensor cause its easier to tune but its also much less acurate a metering air flow. All turbo Subarus use MAFs for a reason . Anyhoo, to get back to the topic at hand... OEM's use diverter valves, the 1G DSM and GD WRX are very similar and very very good (until you get to 19-20+ psi). You vent the air back after the MAF but before the compressor. What the valve actually does is vent the pressurized intake charge when the throttle plate shuts. Over time (ignoring the increased lag) a turbo w/o a DV or BOV will slowly be beaten to death by the pressure build up between the closed throttle and the compressor wheel.
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