[audi20v] Re: Turbo'ing your CQ!

[QSHIPQ at aol.com]

Let's not forget Audi Sport adding a fuel injector to the exhaust manifold to 
the rally cars.  I saw at Monterey they took it off the S1, but you could see 
the mounting plate where it was.  

Jukka, your description of the pop off valve vs the bypass valve isn't 
accurate.  Let's clarify...  Both of the items you describe below are bypass 
valves.  A bypass valve can vent to atmosphere, or to the intake tract.  Most 
use it closed loop, as the theory is that once air is measured, it should go 
thru the motor.  Some race cars vent them to atmosphere, as it does richen 
the mixture.  The problem with doing that on a street car is two fold, 
catalytic converters melt/clog, and O2 sensor toast (neither of which is used 
on a race car).  That said, audi sport used them closed loop very early on in 
racing.   A pop-off valve is an absolute boost device, it's job is to prevent 
overboost, that's all.  Indy cars use them, so do many of the tweeked turbo 
cars.  Their job is to dump all boost at a preset boost value measure in the 
intake system.  A bypass valve is designed to prevent boost spikes from 
stalling the turbo (or blowing the end caps off the IC - btdt many times) 
caused by sudden throttle shut while on boost.  Bypass valves *DO NOT* 
prevent overboost, since they are closed based on boost pressure + diaphram 
spring pressure.  IN *all* audi turbo applications it *only* opens with 
vacuum applied.

You won't find any difference wrt lag between a bypass to atmosphere and a 
bypass to the turbo, bttt.  *IN* fact, even the audi S1 rally car bypassed to 
the turbo with 3 entry points, angled at the turbo intake blades (supposedly 
to blow on the blades to keep them spinning - doubt it's effective with 
anything less than those big dog turbos audi sport used).  

Boost regulation is only provided by wastegate and it's regulation.  Neither 
bypass or popoff valves "regulate" boost.

HTH clarify

Scott Justusson
QSHIPQ Performance Tuning
Chicago IL


In a message dated 8/29/00 11:59:53 PM Central Daylight Time, jiipm at sci.fi 
writes:

> 
>  >They're called "bang-bang" systems, after the noise those puffs of black
>  >smoke bring out. Check out www.rallycars.com/Cars/bangbang.html.
>  >-Ian Duff.
>  >-----Original Message-----
>  >From: Quincy Chiang [mailto:qccq at hotmail.com]
>  >Sent: Tuesday, August 29, 2000 2:00 PM
>  >To: Audi 20V
>  >Subject: [audi20v] Re: turbo'ing your CQ!
>  >
>  >
>  >Bernie,
>  >
>  >There's an article from either C&D or R&T a while back, about the rallying
>  >Imprezas that prodrive builds for Subaru.  It described an anti-lag system
>  >similiar to what you've described.
>  >
>  >The computer essentially dumps extra fuel into the hot exhaust manifold to
>  >keep the turbo spooling at all time, thus eliminate lag, and you see puffs
>  >of black smoke out the tail pipe all the time.  Of course those being real
>  >race cars, neither fuel economy nor long term reliability is a concern at
>  >all.
>  >
>  >QC
>  
>  
>  Hi!
>  
>  Can be, but the most common way is to use so called Pop Off valve.
>  While shifting throttle closes and vacuum in the manifold side opens
>  the valve to keep the turbine reving. If it blows out, it will rich the 
> mixture 
>  for a while, causes "pop and bang". 
>  
>  More civilazed way is to recirculate pressure back to intake side of 
turbo, 
>  but no enrichment and some lag ( By Pass valve ).
>  
>  These can also be used to prevent the overboost, but not for regulation.
>  
>  My best
>  j-pm