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BOV's...a little tip

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Old 09-24-2002, 08:45 AM   #41
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Default bless you for these informative posts...

the obvious question for me is for the big turbo A4 owners...is something like these BOV's going to be a good idea with a T28 or GT25 turbo'd A4 which is producing 23+psi peak, and spiking up to perhaps 26psi?

The idea that the valves remain partially open at idle was like a light-bulb going off in my head. Makes me think that the hi-boost shredding of many BPV we see here would be negated by the atmo bleed.

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Old 09-24-2002, 08:53 AM   #42
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Default no meng....

what adaptor are u talking about? there is no adaptor. the H-25 from turboXS is made for the 1.8t just like the forge valves are. you just need to plug up the pipe the re-routes the air back into the intake.

it's pretty much plug - test - and play.
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Old 09-24-2002, 09:25 AM   #43
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Default Thanks for the info! Now my S4 will be perfect!

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Old 09-24-2002, 09:28 AM   #44
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Default Don, can you confirm that these are the right ones?

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Old 09-24-2002, 09:43 AM   #45
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Default Well - I was thinking about this the other night - I don't think the ECU really knows what is coming

back into the system. For example, once it passes through the MAF - its now being compressed by a turbo, but does the ECU know how "much" air is going to be coming back on an off throttle situation? I am not sure the Motronic system is smart enough to calculate turbo 'efficiency' - but hey, who knows... The reason I don't think so is that from swapping to K04s, I have had no such issues, and the volume of air being recirculated has definetly changed from what the K03s used to do. Also have to keep in mind, that with a BPV, you're recycling "Hot" air - so that may be a slight performance hindering issue - probably not too noticeable, but for the one who wants 100% performance, that .1% is everything I guess.

I just don't think the ECU is smart enough to know how much air should be coming back, I mean when you're at different throttle positions at different RPMs, the compressing of the air's efficiency is always changing so the amount of air bled off is a constantly changing factor.
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Old 09-24-2002, 09:54 AM   #46
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Default Thanks Don! I still have a question about the design with a MAF though.

The number one reason most people on this board attack BOVs is because they feel that any car that runs a MAF will run rich. When you vent air that you have already metered into the atmosphere your vehicle will dump too much fuel into the engine. How is this circumvented? Does this not happen?

Do you plumb the BOV directly to the manifold or do you still use the advanced electronic controlled S4 system for the BOV control (valve N249)..

thanks
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Old 09-24-2002, 10:07 AM   #47
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Default Does it matter how much is coming back??

If it's compressed it still has to come through the MAF and it will get metered. As air passes through the MAF the vehicle knows how much is entering the system and will provide the fuel necessary. Even if it get's compressed, the air still has to pass through the MAF, it has to get that air from somewhere? The ECU knows the ammount of air in the system and as you open the throttle plate it will provide the fuel necessary.
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Old 09-24-2002, 10:09 AM   #48
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Default the mix getting to the O2 sensors is probably how it knows...

indirectly anyway.
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Old 09-24-2002, 10:12 AM   #49
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Default I think he is saying it only runs overly rich during idle (if the valve is misadusted and open)

"this is probably what is happening to those of you that are trying BOVs and the engines run very rich at idle and very poorly, but smooth out when driving at higher rpm....the piston is probably open at idle."

I assume he means that the bov's are open for a short enough time during PROPER operation that the car does not run rich for a significant amount of time, unlike at idle, where running rich for an extended period will throw dtc's and result in a rough idle.
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Old 09-24-2002, 10:13 AM   #50
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Default Right - but figure that if it goes back through the MAF, and say you're off throttle for a couple

seconds, once you get back on throttle, I don't really see that the air 'dumped' will increase the volume of air that may already be in the airbox - you know what I mean? For instance, say you have an open intake like an Evo or something(I know they're not "better" than stock, but for example) and you dump the air back in to be "metered", its now in the engine bay for the most part - the sensor isn't measuring air going backwards through the MAF, so I still don't think it matters...
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Old 09-24-2002, 10:15 AM   #51
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Default Yeah I got what he was saying with idle and non-boost applications..

I suppose what I'm looking for from him is what you just said... it will run rich, but it's not enough to matter.. I'm still curious if he's still using the electronic control system for them...
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Old 09-24-2002, 10:17 AM   #52
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Default [edit] but now the extra pressure in the INTAKE system will prevent MORE air from passing the MAF

.. further up the line.
Think of it this way, once the BPV dumps air back into the intake, the VACUUM is less after the MAF, so less air will pass the MAF.

[edit]
in fact, if what Don says is true, and if under HIGH BOOST applications there is enough BPV pressure to blow intake hoses, presumably there is NO longer vacuum after the MAF, meaning air will flow back PAST the MAF backwards, further screwing up the MAF readings.
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Old 09-24-2002, 10:23 AM   #53
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Default Naw, the car runs rich in essense because say for example you take your Forge valve

and disconnect the part that goes back into the intake, and plug that hole - now the vacuum is holding the valve open a bit, so its causing the air to go right into the atmosphere. The car begins to run rough because the system is no longer 'pressurized'... so to circumvent such issues, a stiff/adjustable spring will allow it to stay closed under idle vacuum, causing the system to stay pressurized, and the ECU should adapt accordingly - otherwise you're just having arrant amounts of air fluxuating out of the valve. For instance, if you take your forge valve, and unplug that one end - and put a stiff spring in the forge valve, and used washer's to help adjust when the valve opens (under how many hG's of vacuum) you could make the forge's work as a BOV - the downside to this as some of us were discussing last night, is unless you use a very stiff spring - and use washers or what not to compress the spring some more, you lose some piston travel on release which may or may not be bad. It still opens more than a stock BPV...

The car will run correctly though - a simple test is to open one end of your valve, and tape the end closed, you will notice that your idle will be perfect (do NOT make boost while you have the tape in place).
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Old 09-24-2002, 10:24 AM   #54
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Default ah got it.

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Old 09-24-2002, 10:49 AM   #55
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Default Oh, Ok, so for 1.8T the BOV will be where the BPV is..am I thinking right?

The reason I ask is because I have seen 1.8Ts with BOVs mounted at different locations, but no where near or replacing the BPV..
Thanks.

Jack
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Old 09-24-2002, 11:12 AM   #56
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Default there's about 3 ways to mount a bov on a 1.8t

it depends on which style bov your running.

for styles like the greddy typeS or turboXS type H-25 - they simply plug into where ur bpv is.

for styles like the hks ssq, and "other" turboXS one (the one on the right of don's post) - you need to get a little more creative and get a adaptor or a custom flange. you could also mount these on ur ic return hose (you'll need a custom pipe with the flange welded on), this will run in conjunction with your bpv.

email me if your interested in the second style with the hks, i believe we have a few kits still on the shelf.

-w
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Old 09-24-2002, 11:38 AM   #57
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Default Well...

A couple of things if I understand what you're saying. When it dumps back into the system it's not getting metered again. It's all behind the MAF at this point. Also because the BPVs are open (vacuum in manifold) it just continue to circulate until the throttle plate opens again. If for some strange reason the air did flow back out the intake (maybe the BPVs are malfunctioning?) the MAF is capable of reading return air flow. What it does with these reading I do not fully understand, but it is capable of it.
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Old 09-24-2002, 12:06 PM   #58
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Default I was wondering that too. Must run rich during shifts no? DOn, would you recommend this for......

a street car?
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Old 09-24-2002, 12:55 PM   #59
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Default I WANT BLOW OFF!!!!.....

i have a A4 1.8tqm w/ stock K03 and a Bailey's BPV, WHAT DO I NEED TO DO TO GET A BOV?
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Old 09-24-2002, 01:52 PM   #60
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Default Don what about "engine wash"

The Audis run extra fuel (rich) to lower the exhaust gas temps, removing air and causing the car to run richer has been known to generate engine wash (washing the cylinder sidewalls with fuel) Are you saying that our cars run lean enough for that not to happen? I know Supras and other turbo charged cars have been prown to that when their boost is vented to atmosphere.

Just curious
-Will
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Old 09-24-2002, 01:52 PM
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