BOV's, DV's and the Audi closed loop turbo system.
 

The Audi turbo system is a closed loop system by which all unused boost that is spooled during off throttle and gear shifts must be re-routed within the system; it cannot be vented to the atmosphere due to the dependence on the MAF and ECU to properly read and interpret air flow dynamics within the intake tract. Therefore BOV's (Blow-Off Valves) are not used because they create a rich air/fuel condition (i.e. less air to fuel ratio) which will damage the catalytic converter, create soot on the exhaust pipes, and cause occasional misfiring (due to the purged air) which will result in ECU miscalculated timing adjustments and other errors.

For Audi closed loop turbo systems, a BPV (By-Pass Valve) or DV (Diverter Valve) is needed to recirculate the purged air and keep it within the intake tract.

As of July 2004, the following valves were available on the world market:
AmD Viper = Polished chrome version of Bailey DV with AmD logo, $$$ (see "Bailey" below)
Bailey = Probably the most popular, serviceable, $$$
Evolution Motorsports = Cosmetic, 4 color anodized choices, not serviceable, $$
Forge = Large (may have fitment problems), serviceable, $$
Forge 007 "A Line" = Same as standard Forge, flat top for better fitment, seviceable, $$
Forge Race = Larger than others (see above), adjustable, serviceable, $$$
GFB Stealth FX D-BOV* = Exclusive unorthodox design, externally adjustable, tight fitment, not serviceable, $$$$+
HKS SSQV BOV** = Dual stage pull-type relief valve, highly competitive for open loop systems, not for Audi turbo sysytems, $$$+
HKS Racing BOV Type II** = Single stage aluminum pull-type valve, same as SSQV but able to handle up to 43psi (3.0 bar), $$$$+
Hyperboost = Cosmetic package, not serviceable, $$
Hyperboost Adjustable = New, cosmetic package, may not fit S4, adjustable preload, not serviceable, $$$
Hyperboost HX = Newest, very cosmetic package, new internals, not serviceable, $$$
OE Bosch TT 710A = THE STOCK DV FOUND IN ALL (1997 AND UP) AUDI TURBO MODELS, Audi part # 034-145-710A OR 06B-145-710, $
OE Bosch TT 710N = Basic, popular & low-budget upgrade, maintains stock look, not serviceable, Audi part# 06A-145-710-N, $ (some dealers charge more)
OE Bosch Sport 110 = MTM upgrade, same as 710N with "better" internals, not serviceable, $$

$ = under $50 USD
$$ = $50 - $150 USD
$$$ = $150 - $250 USD
$$$$ = Over $250

* The GFB D-BOV is currently an unproven design; it is a hybrid diverter and blow-off valve; it is intended to act as a diverter valve while providing the cosmetic audible benefits of a blow-off valve; it has yet to be determined/proven whether this design is effective for use on the Audi closed loop system or whether it may be causing long term damage.
** The two HKS BOV's are mentioned here because they have shown up on some highly unorthodox applications on the S4; they were not used properly and eventually removed due to poor recirculating feeds and other ecu errors.

Am I the only one using APR R1 DV's? (not on the list)

http://www.goapr.com/Audi/products/r1.html

Why do people replace these? Do the stock DV leak under a certain amount of boost. do they stay open not allowing boost to build?

hi, i am also in need of information on this. what does this do and since i am new to how the internal of a car component works. Could anyone give extra information on this. I got a 2009 A4 B8 1.8T, so i am interested to know all about the extra stuff i can do to my car :). thanks :)

So, would using the Forge "splitter", DV in combination with BOV, be a bad choice for my 2001 audi TT Quattro 225HP? Or should I just stay with the DV?

does anyone have any news on the AWE Tuning DV1 DV?i just installed it last week and my car makes a weird kind of like fart noise whenever i let off of the gas or step on it again. any help would be nice

I got the Forge Motorsport hybrid BOV/DV and since it's fully ajustable, it made a big change on holding up the boost on my car ( 2000 A4 1.8t Q ), before I change it, my car was holding 15 to 18 psi and now it's 20 to 22 psi without any more mods, but as far as long term damage, I got to say '' will see ''... but I don't think anything bad is gonna happen since the Forge hybrid is 75%DV and 25%BOF.

http://www.namotorsports.net/detail....t_cd/FMDVSPLTR

Putting in forge dv's how much does it deaden the psshhh noise? thanks

if you got a oem air intake you don't hear much but with a short ram intake, you'll hear it don't worry ... I really start hearing the psshh noise when I installed my Carbonio intake ...I start hearing it as low as 5 psi ... and I got Tiptronic tranny and I soon as I lift my foot off the gaz pedal I can hear it ... and it make a great sound to...I will try to put a sound clip ...

bov's on s4
 

so there is now way to get the PSHHHH sound with out sacrificing drivability? do any chips enable the ability to install blow of valves?