What is the best bypass valve for the 200???

auditude at get.net auditude at get.net
Wed Jul 10 19:36:17 EDT 2002

Check out http://www.gofastbits.com.au/inside.htm for that company's take o=
n bypass valves.  Other links
at the bottom as well.  I have no experience with them or any other valve.

Here's the text too:

> GFB Blow-Off Valves are the only valves on the market to boast these
> unique features:
> =B7 The brass piston features a taper that in the closed position seats
> against an acetal seal that means it WILL NOT LEAK under boost. The
> bore also features a quad-ring seal to maintain the integrity of the
> vacuum signal that opens the valve for quick reaction. All the other
> valves in this class rely on the diameter of the piston for sealing,
> and after a while the wear associated with the operation of the valve
> will increase the amount of air that leaks out through the bore.
> =B7 During operation the piston of a blow-off valve shuts rapidly onto
> the stop, where the acetal seal in the GFB valve cushions the impact.
> Other valves do not have this feature, and eventually the soft brass
> piston can become severely damaged, causing jamming problems due to
> brass flakes.
> =B7 Manufacture of GFB products is carried out on the latest multi-axis
> CNC machines under the international quality standard ISO 9000.
> =B7 GFB Blow-Off Valves are physically smaller whilst retaining the same
> high airflow characteristics of other valves, however the smaller size
> means they are more suited to modern engine bays.
> =B7 GFB Blow-Off Valves are versatile. They can be mounted in two
> different ways, either as a push fit inside the factory rubber hoses
> with a variety of different sized fittings to suit all turbo vehicles,
> or they can be mounted onto a 1 inch O.D. steel or alloy pipe.
> =B7 The piston uses less material for low inertia, which translates to a
> faster response time.
> Why Fit a GFB High Performance Blow-Off Valve?
> Four reasons:
> 1) Driveability
> 2) Fuel efficiency
> 3) Boosting up applications (factory valves can leak like a sieve!)
> 4) The noise!
> And How Does a GFB Valve Do All Of This?
> 1-2) Most turbo cars have some form of factory blow off valve
> (sometimes referred to as bypass or anti-surge valves), most of which
> dump the excess turbo pressure back into the inlet to reduce or
> eliminate the associated noise. It is common for factory valves to
> open at very slight vacuum signals, meaning that whenever your
> manifold pressure is not experiencing boost, the valve is wide open
> and is recirculating a significant amount of air from the turbo's
> outlet to it's inlet. This means that for about 95% of the time that
> you are driving your car, the turbo is trying to generate boost but
> can't until the valve shuts. In this condition you might as well take
> the turbo off the car!
> If a slight throttle increase is made (say to maintain speed on a
> freeway up a small rise) and the manifold pressure makes the
> transition from vacuum to boost, the valve closes. So the rather
> significant amount of air that has been pumped around in circles by
> the turbo is now pressurised and directed at the engine. The end
> result is an annoying surge that makes freeway speeds difficult to
> maintain.
> A GFB Blow Off Valve uses the correct spring pressure to keep the
> valve closed until it is needed, so that the turbo's energy is not
> going to waste at light throttle applications. End result? You now use
> less throttle to drive the car around for the 95% of the time that is
> not spent on boost, meaning better fuel economy.
> 3) A factory blow off valve is only designed to cope with factory
> levels of power, and tests performed on a variety of them show that
> they leak significantly at boost pressures as low as 3psi! Why waste
> that boost? It is also important to realise that a small boost
> increase of 2-3psi will quite dramatically increase the speed of the
> turbo and the airflow passing through it, and it is almost certain
> that a factory valve will not be able to vent the required volume
> quickly enough to prevent damage to the turbo.
> Quite often a factory valve will be undersized, and will compensate by
> staying open for ridiculous periods of time. GFB Blow-Off Valves
> utilize an acetal seal in the closed position to ensure NO LEAKS under
> boosted up conditions, and the generous porting will easily vent
> larger quantities of air more rapidly. The spring pressure is also
> adjustable to enable the valve to be tuned to the boost level being
> run.
> 4) If you want people to know that you are driving a turbocharged car,
> you need the WHOOOSH noise between gear changes! GFB Blow-Off Valves
> come in a range of venting arrangements to suit your needs. Choose
> from the silent operation of the plumb back model, to the
> ear-shattering twin trumpet Bovus Maximus. Or for the best of both
> worlds in cars with airflow meters the hybrid allows some air to be
> plumbed back to keep the ECU happy, while still gracing pedestrians
> with that distinctive roar!
> How a Blow-Off Valve Works:
> Most Blow-Off Valves utilise a piston or stem valve, using a spring to
> return it to the closed position. The inlet port of the BOV is plumbed
> into the inlet tract of the engine somewhere between the turbo outlet
> and the throttle body, and is usually arranged so that the boost
> pressure pushes the piston against the spring. The other side of the
> piston is a sealed chamber that is connected to the inlet manifold
> after the throttle body via a vacuum hose.
> When the throttle is open and the turbo is making boost, there are
> relatively equal pressures on both sides of the piston, allowing the
> spring to keep it tightly shut. When you close the throttle rapidly,
> the increase in pressure on the turbo side of the piston and resulting
> vacuum on the manifold side create a large differential, which snaps
> the valve open and allows the turbo to freewheel.
> What Does a Blow-Off Valve Do (apart from the noise!)?:
> The vast majority of turbo owners fit aftermarket blow off valves
> simply for the signature noise that they make between gearshifts.
> While that may be reason enough to fit one, they do actually serve a
> more important purpose than that. A common misconception is that if a
> turbocharged car doesn't make a "whoosh" noise, it doesn't have a
> blow-off valve. Almost every modern turbo car will have some form of
> blow-off valve, except that the vented air is returned to the inlet
> tract before the turbo to muffle the sound.
> A good analogy for what happens in a turbo system when you close the
> throttle is water hammer in household pipes when you turn the tap off
> too quickly. The same thing happens when your turbo is spinning at
> about 100 000 RPM, pumping pressurised air into the engine. When the
> throttle butterfly snaps shut for a gearshift, that air (which can be
> travelling at up to 90 metres per second) has nowhere to go except
> back the way it came and out through the turbo. This is bad for a
> number of reasons. First, slowing the turbo from maximum RPM to
> practically zero in less than a second is obviously going to place a
> lot of strain on the turbo. Secondly, since the turbo has stalled, the
> lag when you open the throttle again is increased.
> The BOV is designed to release excess pressure under these conditions
> to allow the turbo to freewheel, which both prevents damage and
> reduces lag. The noise is achieved simply by venting the air
> externally. Why are GFB high performance Blow - Off Valves BETTER THAN

Other links:

http:// ... eh, you get the picture and can search :-)



Jobe Tichy bimmer_dude at hotmail.com wrote:
> I know I was considering the FORGE because of its ability to be
> rebuilt.
> I have played with them--never ended up purchasing one because my BPV
> wasn't broken the vacuum line was--anyway, they can be taken apart,
> lubed up, and o-rings and the piston can be replaced. I guess just
> recently, the Forge ha=3D ve gone from a nylon piston to a metal piston
> so I suppose they are interchangeable.  In my opinion, it's more
> comforting knowing you can repla=3D ce the parts on it to keep the turbo
> running tip-top.  Also, they're beefy as hell and look as though they
> can take quite a beating.
> As for performance, a buddy with a urS4 has one after I recommended it
> and says he likes it quite a bit.  It keeps the turbo spooled up
> better than the stock BPV, especially since the car's chipped.
> Price--$140 I believe.
> >From: "Audi Sport"
> >
> >I am looking to replace the stock plastic, rubber diaphragmed bypass
> >valve with an after market metal unit. Do any of you know which valve
> >works best  on the  200? Who makes it? And how much is it? I know there =
are quite a
> >few companies that offer bypass valves out there that would fit out
> >cars but which one should I go with? Anyone with experience on this?

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