[s-cars] DahlBack Racing BYpass Valve, why not two.

Wed Sep 24 20:25:49 EDT 2003

The Indy and F1 cars have it on the plenum so that it will blow off with too
much pressure.
These valves are inspected by the officials before and after the race AFAIK.
I asked a mechanic about it this year when I was in the paddock during the
Toronto Molson Indy.
Actually the had a bit of a write up on them on one of the sites around.

I don't really think they require a BYPASS valve for the reason of closed
throttle.
They don't slam the throttle shut to shift, they don't de clutch for that
matter either.
Ain't sequential air powered shifting wonderful :)

I have heard of a sequential box for the Audi, any BTDT or similar on it ?

Mark S
----- Original Message -----
From: "Trevor Frank" <tfrank at symyx.com>
To: <QSHIPQ at aol.com>; <CaptMagu at aol.com>; <airs41994 at hotmail.com>;
<s-car-list at audifans.com>
Sent: Wednesday, September 24, 2003 2:00 PM
Subject: RE: [s-cars] DahlBack Racing BYpass Valve, why not two.

> This is a multi-part message in MIME format.
> --
> [ Picked text/plain from multipart/alternative ]
>
> Ths was basically my thought Scott, I have a ricier than you, purple
> adjustable Gretty type S as my primary valve and a Gretty type R that I
> was thinking of placing on the t-body side.  Although I haven't had luck
> with the bosch valves I do like diaphragm valves for two reasons.  1 it
> takes a little more r and d and cost to manufacture.  2. I suspect that
> like the bosch the actual mass of the moving components is less on a
> similarly sized diaphragm valve.  My personal favorite is the idea
> turbonetics has with there trap door style valve.  Hap mentioned the
> pressure wave issue and so did Scott.  Many bov manufacturers recommend
> the bov be placed close to the t-body, indy car and F1 have it mounted
> on the plenum.  I suspect with such a large volume there is quite a
> disconnect and possible disruption that would occur after the bpv opens.
> My lead in was mentioning pressure drop be it 1psi or 3 either way it is
> a tortured path back to the bpv from the t-body.
>
>
>
> I mentioned two reason's for the second valve, as a disscution point,
> one was a simple mechanical safety valve to save the motor incase of
> some issue with the bpv/wastegate.  The other would be a second bpv/bov
> to vent some standing wave that may occur in this volume, in this case
> controlled by the vacuum.
>
>
>
> Not to start the bosch debate again but let's just say I have scrambled
> one, and the ball bearing turbo's don't like injesting plastic/rubber.
> Even though I am positive due to inertial mass that there is very little
> chance that any other bpv would react quicker.
>
>
>
>
>
>
>
> On to Ned's comment, I suspect on a race motor that keeping the turbo
> spinning would be more important than issues of trying to stall the
> compressor.  The slight annoyance of the noise and damage that may be
> done would be secondary.  I suspect you would also have to be careful
> coming to a complete stop without keeping your foot in it as to not
> stall the turbo, and the motor completely.  A higher idle speed may also
> make this possible without stalling the motor.  Of course I could be
> completely off.
>
>
>
> -----Original Message-----
> From: QSHIPQ at aol.com [mailto:QSHIPQ at aol.com]
> Sent: Wednesday, September 24, 2003 2:39 AM
> To: CaptMagu at aol.com; Trevor Frank; airs41994 at hotmail.com;
> s-car-list at audifans.com
> Subject: Re: [s-cars] DahlBack Racing BYpass Valve, why not two.
>
>
>
> Several years ago, I proposed that those with monster turbos might
> explore 2 bypass valves and stagger them so that the first opens under
> light lift (vacuum) the second opens under full lift.  The
> bigger/heavier the valve components, the longer the transition back to
> boost (valve shut).  I've played extensively with the HKS sequential
> BPV, which to me is a great idea, but the light lift wasn't enough
> bleedoff.
>
> 2 adjustable preload bypass valves could be just the ticket.
>
> WRT MLP's comments on placement...  Had numerous (humorous?) discussions
> on this very subject.  In *theory* you want to place the BPV as close to
> the tbody as possible, since the reason for it is to bleed the pressure
> wave, which starts at the throttle body and migrates back to the turbo
> blades.  Another theory presents itself that postulates that you want
> the turbo to freewheel as soon as you lift throttle (vacuum present) and
> it will freewheel the fastest when located close to the turbo.
>
> In *practice*, IME, the BPV closer to the T-body is faster to react to
> boost/vacuum transitions, but the choice of BPV probably makes a bigger
> difference (IOW a stock valve is quicker than a big heavy valve).  That
> said, I believe my posts of yesteryears have postulated that a quick
> light vacuum valve (stock or "small") might be best at the T-body, and
> that mongo big dog with a lot of preload, sit prior to the IC.  My
> *theory* being a quick shift doesn't need a full boost dump, but a full
> lift most likely means you don't need to worry much about transition
> back to boost.
>
> I also believe in that 6 year old thread, that Graydon Stuckey said you
> really don't need ANY bypass valve if you keep the throttle body open
> slightly between shifts.  If you look at the decel delay valves audi
> used on turbo cars (including S) since 1988, this appears to be a valid
> idea.  And in/with practice, it works.
>
> HTH
>
> Scott dubbledummp Justusson
>
> In a message dated 9/23/2003 10:48:30 PM Central Daylight Time, CaptMagu
> writes:
>
> Trevor
>
> It seems to me that Dave Jones, Mike Pederson and I have had numerous
> conversations on this very subject. Mike and I have experienced a boost
> pulse  that we thought might be helped by this solution. I can't
> remember if Mike and Dave tried this or not. The pulse is particularily
> acute when I'm really loading the turbo as when I make the climb up I-70
> on my way home to Everboost. It manifests itself on throttle lift after
> serious boosting especially if I only partially lift the throttle.
> Without total lift and resultant vacuum it might be tough to get the BPV
> to open. HTH.
>
> Hap, to boost or not to Everboost, Maguire
>
>
>
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