[s-cars] First of my own wrenching of my '01 S4

[Kirby Smith]

This may be a good time to add a few comments on a valve not covered by
the comparison referenced below.  This valve is distributed by Dahlback
Racing through his US importer TJM Motorsport in Concord, NH
603.229.0494.  My relationship with TJM is that Tim McLean has been my
mechanic since about 1985.

The Dahlback bypass valve resembles the Forge valve.  I installed a
Forge valve a few years ago when my stage 1 ECU setup caused the stock
valve to start honking.  The Forge was purchased from Stratmospher.  The
Forge valve worked fine.  I eventually replaced its original plastic
piston with the metal one, provided at no cost by Stratmosphere, but
miking the plastic piston showed no distortion.  At the time of Forge
installation I provided this list with my measurements of pressure
parameters, but I can't find them now.  Used Forge valve values are
included below.

The Dahlback valve was provided to me for testing at no cost other than
my installation time.  Before installation I measured its parameters
versus the Forge being removed.  Units are cm Hg (in Hg).  Pressure is
at the manifold control port.

			Dahlback			Forge
Leak Pressure		11. (4.5)			8. (3.5)
Full Open Pressure	24. (9.5)			24. (9.5)

As I recall, I had installed the lighter of the two supplied springs in
the Forge originally, as recommended by someone on this list.

Behavior of the Dahlback unit is fine.  With my mere 1.3 barg system I
can't really exercise its limits.  I do not notice any improvement or
degradation in performance from it relative to the performance of the
Forge valve.  

I did not do the piston pressure tests of the web site listed in the
message below.  I do not believe that test really matters for either of
these two valves because the back of the piston sees intake manifold
pressure, so whether hooked up normally or reversed turbo pressure will
not cause the valves to prematurely open.  What might change with
orientation is dynamic response, but I have no way of testing that.

Some competing valves have fins.  I believe they are as likely to absorb
heat from the exhaust manifold radiation as emit heat.  A slight
convection cooling advantage may be present, depending on air flow near
the fins.  I would like some measurement data before I thought that they
provided significant cooling.  In any case, the only components of the
valve that are influenced by heat are the O-ring seals.  Suitable
materials for the temperatures involved have been available since at
least the '60s, so my feeling is the fins are chasing a non problem.

Bottom line, if you have a Forge or similar unit and it is fully
functional, there seems to me to be no point in replacing it with a
Dahlback, as far as I can tell with my car.  On the other hand, if you
are planning to upgrade from the OEM bypass valve, the Dahlback is an
eminently suitable replacement.  In that case, give Tim a call. 

kirby, running the Dahlback bypass valve.


Doug Landaeta wrote:
> 
> Steve,
> 
> Bob, nice summary on the air filter Bob! There's a
> plethora of discussion on this, but I'll opt for
> the gist, as you've posted.
> 
> On the by-pass valve or pop-off valve, or
> blow-by-off valve, I enjoy referencing the
> extraordinary work done at
> http://dv.mistertam.com/
> 
> Doug L
> 94 S4 mit 710 and paper
> 
> > -----Original Message-----
> > From: Bob Rossato [mailto:bob.rossato at att.net]
> > Sent: Tuesday, March 09, 2004 9:52 PM
> > To: Single Malt; s-car-list at audifans.com
> > Subject: RE: [s-cars] First of my own wrenching
> > of my '01 S4
> >
> > With regard to the BPV, there will be a myriad
> > of opinions on this list as
> > to what is the best type of BPV out there, but
> > the part number you are
> > referring to from the TT is 06A 145 710N.
> > Though some folks that have tried
> > them say that they also fail.
> >
> > With regard to the K&N filter, I know several
> > folks on this list use them,
> > either in flat panel or cone shape, but I've
> > never been a fan of using these
> > types of filters on street cars.  The premise of
> > the K&N filters is that
> > they allow more air in than a stock air filter
> > and thereby should result in
> > more power.  That's all well and good but there
> > are several reasons why they
> > are not a good idea.
> 
> Yada yada yada...
>