WG connection, EM design

auditude at cox.net auditude at cox.net
Sat Dec 7 15:01:29 EST 2002

On 7 Dec 2002 at 16:40, JShadzi at aol.com wrote:
> Ken wrote:
> <<What is the advantage of having the wastegate exhaust source come directly from the
> individual cylinders, rather than after they are combined, in this pic:
> http://pr0nsessd.dyndns.org/qul_irry/tacq_files/gul20.jpg
> This is assuming I am understanding what the plumbing is doing.>>
> Ken, its tough to know exactly what the user was doing from this picture, but that looks an awful
> alot like the Audi Sport anti-lag system, where intake pressure is vented back through the turbine
> instead of going to atmosphere to keep the turbo spooled. If so, bravo, that's a trick and very
> nice piece to have on a turbo car, especially with a large turbo and high hp.

Yeah, I guess that is a sport quattro motor actually.  I look at some other pics, and saw that
it had the gear driven cam and two injectors per cylinder (crazy!).  I guess it's a long
wheelbase SQ, or whatever iteration that would be called?  It looks like a regular ur-q, but
has the single headlights.

So, the way the SQ system works is that the bypass valve output is directed into the exhaust
manifold, instead of the turbo inlet or atmosphere? Or, does this system do something more
than just when the throttle is closed?

Is it a requirement that there be no/little valve overlap for this system to work?  Seems like
the flow would go backwards if there was overlap.  But that would be the case even without
this system, right?  Since the exhaust has more pressure than the intake under boost,
doesn't it?

Is it possible that exhaust gas would go up backwards through that path?  Like you shift at
15psi and the bypass valve opens, can exhaust to backwards through the anti-lag system to
the compressor side, or is the 15psi way higher than the pressure at the turbine?  (I thought
turbine pressure was greater than compressor, as I described above.)

Is it overkill that, if my understanding of the anti-lag system's function is correct, the bypass
valve pressure is introduced at the individual cylinders?  Would it be possible/beneficial to
have a single port on the turbine side of the EM that you could plumb bypass valve output
pressure to?

What effect would introducing bypass valve output into the turbine have?  Would the extra
oxygen ignite some unburnt fuel in the turbine?  Is it dangerous?

So, in effect, the excess boost pressure upon shifting is recycled through the turbo just like
in a regular bypass valve situation, but instead of going into the cold side intake, it is going
into the hot side "intake"?

Also, while I'm typing, what's the deal with "caged roller bearings" for connecting rods?  I
had never heard of this before, but saw some pics online of these.  Is this only for
motorcycles or some specific type of application?  Is it something that can be applied to a 5
cylinder turbo?  I couldn't find any basic data on it, except that it is good for high rpms.



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