Re: Dump valves (was Max boost)

[Daniel Hussey <GY3WSX@vm.sc.edu>]

     OK, One thing.  I don't mean to be picky, but there is a difference
between a dump (or "blow-off") valve and a bypass valve (which is found on a
stock '92 200TQ and S4).  I have been corrected on this before as well.  Just
don't want to confuse anyone.

     A Dump valve literally dumps the excess pressure straight into the
atmosphere.  A bypass valve does basically the same thing (bleeds off excess
pressure), but rerouts it back into the the system before the cold side of
the turbo.  This keeps the turbo spinning in-between shifts and basically acts
as an anti-lag system.  It also prevents back-pressure from when you come off
the throttle from blowing hoses, IC's and stalling the turbo.

     This would be a beneficial thing to add to a modified car.  I don't see
the point on a stock 10V turbo however.  I also don't see the point of using
a Dump or "blow-off" valve.  Why dump it when you can use it.  Solution?  Put
in a bypass valve off a '91 200TQ/S4.  I think this same unit is also used on
a Porsche 944 Turbo.

     It takes a little more creativity and work to plub in the bypass valve,
but I think it should work a lot better than just a dump valve.  This should
help to reduce the dreaded turbo-lag which is so apparent in the 10V cars.
But, if you've ever looked at the hose for this pressure on a 20V you will
notice it is VERY small, so I don't know if it will make a significant
difference.  But, it should prevent you from blowing hoses and the IC.  And,
that seems worth the trouble right there.

     THE THING I DON'T UNDERSTAND IS why it would create any more of a rich
condition (off full throttle) than without one!???  I really can't figure out
why it would!  I mean, that pressure (air) is not entering the intake anyways
since the throttle plate is closed.  So, why does it matter what happens to
this back-pressure.  It can just run upstream and cause your turbo to stall and
create more problems.  And, even if it runs a little rich just off throttle
(littleraly for only a second) would it creat any problems?  I have thought a
lot about about it, and can't see why installing a bypass valve would create
any problems, but I don't actually have one.  Anyone out there with a different
view or any different thoughts....I'd like to hear them.

     Later,
     Dan