SA4T

it seems to me that being lean is about 10x(not proven value) worse than being rich. Ok so it backfires big deal except it might make you look dumb. What other damages could happen, true ECU would get screwed maybe. but what SERIOUS mechanical problems.
ok flame me, I'm rare

Hawaiiannights

All the people who complain about BOV are the ones that don't have one....the guys that do are all happy with theirs.... Read on......

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @@@@Here is a bunch of BOV related info i collected a while back. i got them from previous posts.

Blow Off Valves
Posted by ChrisR on 2000-02-29 15:14:18:

In Reply to: Consequences of blow off valve for all turbo cars or just the 1.8T?? Who has had problems
with it? posted by Shoe on 2000-02-29 14:41:57



This has been addressed up the wazzu....I even checked the archives about it for you,
looking for one good conprehensive link, but there were so many good posts why
replacing the bypass valve on an A4 is dumb.

A summary of what the posts i read state that a blow-off valve can/may do the
following:

1) screws up fuel/air mixture
2) wastes energy
3) loss of power
4) causes mis-shifts???
5) increases turbo shaft fatigue

I dont know if all of these come into play, but some posts in the archives do a good job
of explaining these various points.

So it seems if you want your a4 to make a "cool noise" and DECREASE performance at
the same time,
install a Blow-Off Valve....

ChrisR


Blow-off valve is a bad idea. Always use bypass system
(more)
Posted by Brett- APR on 1999-08-28 22:59:49:

In Reply to: anyone running a blow-off valve experiece any problems.... posted by k on 1999-08-27
12:17:31

It is a bad idea to use a blow-off valve without recirculating back into the system. With
a standard blow-off valve venting to atmosphere, the air-flow meter is fooled and thinks
that the engine is getting this air. So the computer dumps in the appropriate amount of
fuel that it thinks the engine needs to match the measured air. So the engine gets a
VERY rich mixture. Next the O2 sensor senses this rich mixture and attempts to adapt.
This adaptation can alter the air-fuel learning values in the ECU. These instantaneous
rich-mixtures can post-ignite after exiting the turbocharger and cause damage to the
catalytic convertor. Also, the computer normally cuts off fuel during gear changes. With
a blow-off valve, the computer thinks the engine is still demanding air and fuel is not
cut off. Gas-mileage will decrease. Another disadvantage to blow-off valves is that they
often interfere with idle transition.

Avoid blow-off valves. If you are interested in upgrading the stock bypass valve than
buy a quality bypass valve and plumb the vent back into the air intake system.

Brett
Audi Performance & Racing

In Reply to: Why oh why oh why would you do this??? posted by Just blowing off a little!! on 1999-09-01
22:54:39

Wow...It's been months since I last wrote the original post. I was never able to find
followups to my original post until now. (Silly me)

Anyway,

I'm not interested in getting the aftermarket blowoff valve for performance benefits. I'm
merely interested in only for the sound. It does sound cool. =)

A blowoff valve IS essentially the same thing as a by-pass valve. You're right when you
say that the blowoff valve will vent to the atmosphere, but I know that it does not vent
ALL excess boost pressure out to the atmosphere. Only enough of what is really
necessary. I would pretty much set it to be a little more stiff than what stock is now.
(I'm running 1Bar of boost or 14.7 psi) You can totally adjust the setting by a nut. If we
were to talk about performance, then it would DEFINTELY make sense to run an
aftermarket blow off valve if I were boosting a crazy amount such as 2.0bar and above.
The aftermarket valves utilize stiffer springs within the core and are able to support
higher boost pressures without leaking.

But you have to think about this part. When the stock blowoff valve recirculates excess
boost pressure back into the intake, it doesn't change anything. It would make no
difference if it recirculated it or if it was lost. And with an aftermarket blowoff valve, it
does the job of a stock valve except that it vents the extra energy into the air.

Boost level will be different based on ambient conditions, but remember...Your car is
extremely intelligent. There are all these sensors which communicate and send signals
to your ECU. The mass air sensor and manifold air pressure sensor determine how much
fuel your ECU will command to dump into the engine. When the stock bypass valve
recirculates excess energy back into the engine, it goes in after the MAS sensor and
before the MAP sensor. This recirculation will not disrupt or even affect the stock
amounts of air traveling in, or pressure entering. If you don't believe me, ask the people
who actually have these blow off valves installed onto their cars.


Why not reroute the BOV to act like a by-pass?
Posted by Nicholas Wong on 2000-01-18 18:24:56:

In Reply to: Running rich? posted by Cris on 2000-01-18 09:35:34

If you are scared at the possibility that the ECU won't be able to handle the rich
condition, you can reroute the BOV to act as a by-pass. It won't be as loud as if it
were to vent to atmosphere, but your engine won't stall or bog.



In Reply to: BLOW OFF VALVUE QUESTION posted by josh on 2000-02-01 20:48:49

When you vent a blow-off valve to atmosphere,you are 'blowing off' metered air.

Just before air exits the airbox it is measured at the mass air flow sensor. This
measurement is very important and is one of the main variables that is used by the
engine computer to calculate timing, fuel, etc. When you shift a car with a blow-off
valve venting to atmosphere, you lose some of this measured air. Consequently, the
ECU thinks that the engine is getting more air than it really is, and the ECU tries to
compensate.

What are the consequences? Well, you won't lose any HP but the car may stumble
between shifts. The biggest problems would occur when depressing the clutch and
letting the engine speed drop back down to idle- the engine may stumble or even stall.

So our recommendation is to always use a valve that recirculates back into the intake
tract.

Brett
APR




From:Minneapolis, MN USA
Registered: Jun 1999
posted 04-02-2000 01:29 AM

I find it hard to believe that the VAG 1551 or VAS 5051 are able to monitor the volume of air going through the bypass
valve, since that would require a second airflow sensor, and it would be useless data to monitor the air flow from the
bypass valve(read on to find out why). The way B5BAR knows that the stock bypass valve isn't enough is because my
Garrett chipped 1.8t has some pretty nasty torque reversals, that he's experienced riding in my car. Now that I've modded
my airbox so I can hear what's going on (instead of having all that crap in there to attenuate noise)I can tell audibly what
happens when I get a nasty bad feeling torque reversal. I dip into the throttle from 3/4 to full throttle, the boost builds as
the car accelerates, and then I let off the gas for some reason and then *OUCH* torque reversal results in a weird double
reversal with surge in between. By the sound of things, the bypass valve is not opening until after the middle surge, and
then things go back to normal. This leads me to believe that the stock bypass valve is not quick enough in it's response. It
could also be that it's just not designed to flow enough air to relieve 1 bar of boost in that short of a time frame. For most
driving situations, the stock bypass valve is fine, but at times of full boost, my car's bypass valve falls flat on it's face
regularly.

Now since you're obviously worried about metered air escaping, then you should not do this mod since it will make you
paranoid that your check engine light will kick on at any moment. For those who've already done this mod, they can attest
to the fact that it will not cause the MIL to light up. If you're worried about the engine management system being
confused, stop and think about that for a moment. When the bypass valve is open, or a BOV, the throttle plate is CLOSED.
Modern engines like the 1.8t have a closed throttle switch, that signals the ECU to cut the fuel supply off since you
obviously don't need to be burning fuel when you're decelerating. So while the BOV is venting excess manifold pressure, no
fuel is being burned anyway, thus it doesn't matter how much air the motor is consuming or losing through the BOV. If the
BOV were to be set too low though, so that it would vent boost under load conditions, then it would confuse the ECU. If
you don't believe me that the ECU shuts off the fuel injectors, thus stopping fuel flow, check with your local trusted
mechanic. This fuel shutoff feature has been in use since the early Motronic fuel injection systems.

So the moral of the story is, BOV's are fine to run in a 1.8t, even though it is an OBDII compliant motor that monitors a
whole slew of info, because the 1.8t motor couldn't care less about how much air is moving through it when the throttle
plate is closed, because it is not using any fuel at that point in time. Does the 1.8t motor *NEED* a BOV, no they have a
bypass valve already, but it's capacity *IS* questionable. Do BOV's sound cool yes.

Why do APR and Garrett say they are not necessary, well stop and think again. Say you buy a chip, do you want to have
to buy an exhaust, and cams, and BOV, just to make the chip work right? No. Chip vendors and tuners are more than happy
to sell you one piece of the puzzle at a time, and do not want to force you to buy more than one piece at a time since that
could impact sales. Each upgrade component for your 1.8t car costs a pretty penny, and we all work hard for those
pennies. The last thing a chip tuner wants to do is make us feel like we're not getting a good deal for the money. So the
better question to ask would be whether a BOV could compliment a 1.8t motor, even though it is not absolutely necessary
from a funtional standpoint given the presence of the stock bypass valve. That question has already been ansered by
Memin who is obviously happy with his HKS super sequential BOV. While I respect the work and products of APR and
Garrett, I will not accept repeats of what they said as gospel, especially without the full context of the question being
asked. They too have their own agendas, as do I, and everyone else here.

To answer Scott H's question, the BOV does not go between the intercooler and exhaust. The best spot to mount a BOV
on a 1.8t VW is on the tubing from the intercooler to the intake manifold. The BOV and bypass valve only function as
pressure release valves. The speed of the turbo's rotation, and consequently the boost is controlled by the wastegate
which directs exhaust gases either solely to the turbo's exhaust turbine, or through a bypass route that skips the turbine to
slow the turbine down. On some older turbo applications before the heyday of enviromental regulations that we're in, the
wastegate would just open up a second exhaust path that would dump out separately from the main exhaust which spooled
through the exhaust turbine, thus it being called a wastegate. The gate opens, and dumps excess waste gases.

To all you naysayers out there who are always super skeptical about all mods, just wait it out and see before opening your
mouths. If you're uncomfortable with the risks involved with a certain mod, don't do it to your car, but don't go telling other
people how they should or shouldn't mod their cars. You own your car, and you're the boss of your car. Do with it as you
please, and respect other peoples' rights to mod their cars as they see fit.

As always, your results may vary...

-Brian


bhjelt

Your statement is true under the condition of a closed throttle plate. But BOV activation is not directly dependent on
throttle position. It depends on air pressure inbetween the compressor and throttle. So it doesn't take a closed throttle to
open a BOV, when you back off the throttle from WOT partially, the BOV might open depending the preset pressure. At this
stage, fuel is still being supplied and mixture is calculated partially from metered air so you could potentially run rich.

I'm not paranoid about setting my MIL light(I have VWTOOL and I can reset any fault codes if I wish), it's just that I feel a
BOV is not needed at 1BAR of boost and have the potential to confuse the ECU.

If anyone is worried about boost spikes, get an upgraded bypass valve. I believe Autothority makes one and you can also
modify a 944Turbo bypass valve to work with the 1.8t.

Garrett/AWE and APR are very honest to their customers, they don't sell you something you don't need like some other
vendors. If a BOV is really needed, don't you think APR would include it in their stage III kit? After all, it comes with almost
everything you may need so what's another 150 on top of 5 grand. My experience with the 5bar FPR is an perfect example.
I called up AWE wanted to order a 5bar FPR, Todd told me I do not need it after he learned I have the K03 and Garrett
chip. I called up the other vendor and they told me it will give me more power with the GARRETT chip! btw, this is the same
vendor selling the BOV.

If you feel you're getting torque reversal(it could very well be the motor mount compressing when you lift off the throttle)
from listening to your engine, then by all means get a BOV. I wouldn't get one until someone shows me real data or a
reputable tuners recommend it.

------------------
-dingster
For Sale:
99 Passat 1.8tm
Silver/Black, PJ6,
K&N Filter, Garrett Stage 1.5

On order(ETA 5/30/00):
00 Audi A41.8t, Silver/Onyx
Quattro
conv pkg, sprts pkg, sprts seats, xenons, cold wthr pkg, Bose, SideGuard.

[This message has been edited by dingster (edited 04-02-2000).]

IP: Logged
B5BAR
VWvortex Junior Member

Posts: 64
From:minneapolis minnesota
Registered: Feb 2000
posted 04-02-2000 02:52 PM

Sorry to come off strong before.
I just wanted to add, By adding a BOV it is not necessary to vent to atmosphere. There are ways to pipe the wasted air
back into the air stream without effecting any reading on the air flow. You could do this by installing a T where the Stock
Bypass valve is located. This T would let the BOV share the hole where the stock Bypass valve would vent back into the air
system, and since the Stock bypass valve is actually a glorified one way valve, it wouldn't effect the Stock part.
But even with that option I doubt I will do it that way. Yes I am guilty of liking the sound of the BOV, but after talking to
other turbo car owners (Non VW). They say that their stock bypass/BOV cannot handle more than stock boost. Most would
have kept their stock part, but because of the non-adjustable nature of the stock part's in their car's that wasn't an
option.
Also some manufactures want the turbo nature of their cars kept quiet. And with the Passat that I own it seems that
everything is designed to be efficient and Quiet. Just look inside of the engine compartment. You will see all sorts of sound
Shielding that doesn't need to be there (granted some is also intended for Heat shielding that you shouldn't remove) . If
you have time to look inside of your airbox you would see a design that is intended to create a sonic barrier between your
ears and the turbo.
Yes I know that you can obtain an upgraded Bypass valve from various vendors, but they still are not adjustable. I plan on
doing more than just chipping my Passat so having something adjustable will help me in the future.
I have also gotten the same feedback from AWE about bypass valves, but not from Garret or HKS who both have A4 Audi's
and Passat's as project cars. One thing you can definitely say about any private tuners like ourselves and even companies
like; AWE, Garret, HKS, and even Greed Speed, We are all separate tuners who will sometimes come to the same conclusion
about a specific modification and allot of the times not. When different people come to an opposite conclusion that is the
point when conflicts arise. That is also the time when the private tuner has to decide which way to go. I have decided to
go the BOV way because I like the adjustability and Quickness of it, also because I like the sound (I can't hide that). I can
also afford to possibly trip my MIL to save my precious K03, even if I don't think that will be an issue.
Best of luck to all of you on your turbo tuning endeavors. All In all I hope all of you are having as much fun with your VW's
as I am, even if we do things different ways.




chris86vw
VWvortex Junior Member

Posts: 80
From:north brunswick, NJ USA
Registered: Feb 2000
posted 04-02-2000 07:04 PM


quote:

Originally posted by dingster:
bhjelt

Your statement is true under the condition of a closed throttle plate. But BOV activation is not directly
dependent on throttle position. It depends on air pressure inbetween the compressor and throttle. So
it doesn't take a closed throttle to open a BOV, when you back off the throttle from WOT partially, the
BOV might open depending the preset pressure. At this stage, fuel is still being supplied and mixture is
calculated partially from metered air so you could potentially run rich.



Yes but you can set the BOV to only open at boost levels taht would exceed those of when the throttle is open. So that it
would only open when you let off the throttle and the boost build up pressure on the closed butterfly. It also serves as a
back up if you wastegate breaks. And for those of you who think they don't I have seen several go bad on Passats at
work. Luckily they all broke in the open posiion but who is to say that next time they won't jam closed. Having that BOV will
blow off hopefully enough boost to not damage the engine and let you know something is wrong becauseit feels like you
just added a 70 shot. I for one will be eventually adding a BOV both for he sound and the added safety, which no matter
what it does add. But for now there are more important things to do.

chris
chris86vw@aol

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KingVR
VWvortex Junior Member

Posts: 10
From:Boca Raton, Florida
Registered: Jan 2000
posted 04-02-2000 08:44 PM

Just to clear things up, I recall Memin mentioning that he was getting exhaust popping/backfire after he let off of the
throttle. In that specific post, he did NOT mention that he had a B.O.V. on the car. Though in a post that he had made
previously, he made mention to his new B.O.V. that he recently purchased. This IS because the ECM sees a large amount
of air flow still coming through the Mass Air Sensor. The MAS [or MAF] detects a VOLUME AMOUNT of airflow, NOT the
DENSITY of the air. The MAP (Manifold Absolute Pressure) sensor tells the ECM the density of the air, whether the intake
manifold is under a vacuum or pressure. Remember, the intake manifold consists of everything between the throttle body
and the backside of the intake valves. This does NOT include any component before the intake tract 'upstream' of the
throttle body.
With a quiet exhaust system you won't notice it, but if the throttle is shut above 2,000 rpm's it will operate the injectors
for a short moment, anticipating the throttle to be opened up again, allowing it to have a batter response time. However if
the throttle is shut below 2,000 rpm's, the injectors will stay operational to give optimum response time. The BEST B.O.V.
that I can recommend would be the Greddy Type-S. This is because it allows the user to install a hose routing from it's
discharge outlet back to the inlet side of the turbo, (be sure this location is between the inlet of the turbo and the MAS).
The way that a B.O.V. functions is in accordance to the amount of vacuum in the intake manifold. If you're on the throttle,
[metered] air is entering the intake manifold and eventually becomes pressurized from the turbocharger spinning at a high
rate of speed. Once you shut the throttle you are stopping the pressurized [keep in mind, it is metered] air from entering
the engine. With the engine still running [obviously] the pistons are still attempting to pull air into the engine, but with the
throttle body closed shut only a very small amount of air is capable of entering the engine, causing the intake manifold to
become under a vacuum. Absence of pressure is vacuum...vacuum is a fluid (liquid or gas) pressure that is anything less
than 1 bar (14.7 psi), which is how we define "Pressure at sea level = 1 bar." Another term for "1 bar" is "1 Atmosphere."
Since our neat little B.O.V. is operated by vacuum pulling on a diaphragm, this is how it opens and shuts when it needs to
be. Since we don't want unneeded stress on the turbo and throttle body, we can relieve the pressure from the turbo by
releasing it. And because the air from the turbo has been metered by the MAS, it should under no circumstances by vented
to atmosphere. The B.O.V.'s discharge should always be re-circulated on a vehicle with a MAS sensor. If the engine
management system happens to be of the 'Speed Density' variety, (having no MAS meter), venting to atmosphere would be
acceptable because these systems rely entirely upon intake manifold pressure. Vehicles that have this type of type of
management include Mazda's RX-7, Pre-89 Ford 5.0's, and nearly all Honda/Acura cars just to name a few.
The possibility of over-spinning the turbocharger while the B.O.V. is venting is virtually impossible. This is because the
exhaust turbine has very little pressure upon it. The low(er) pressure against the turbine is caused by the following things:
Throttle being shut/the B.O.V. venting pressure [and being re-circulated]/the MAP sensor telling the ECM that there is an
absense of air pressure [vacuum] present/the MAS telling the ECM that there is very little air content being consumed by
the engine. After all of these actions occur, the exhaust turbine will not have the high pressure exhaust present to spin it
at high speeds, leading it to 'free-wheel'.
My suggestion would be to purchase the Greddy Type-S unit, because it features two options: One to open under an
adjustable vacuum load, or as a Pop-off-Valve [P.O.V], allowing it only to vent only when a pre-set max boost pressure
level has been reached. When the throttle is shut, the pressure level will jump, causing the P.O.V. to vent only the
pressure above your setting [i.e. 20psi when your WOT (Wide Open Throttle) boost pressure is only 15-18psi]. You must be
careful though that you set the P.O.V. level to be higher than what the wastegate is set at. If not the wastegate will stay
shut, [Leading to EXTREME overspin, hot air charge, and vastly shortend turbo life], because the turbo will never reach it's
intended boost level which is preset by the ECM/chip/profec etc.
This is all that I could think of for the moment...lol..but seriously, if anyone would be interested in a handbook with material
on this topic, please let me know.

Sorry for being so long,