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Re: UrQ Dump valve

In a message dated 97-11-12 00:59:44 EST, someone writes:

> If your running a stock turbo the Bosch valve is barely adaquate.....  On 
> my car I was Blowing the valve open at 9PSI of boost (Were talking 
> DENISTY Here.......)  I had to go to a HKS race valve to get it to 
> work....
Sounds like someone put the valve on wrong, high pressure goes 90 degrees to
Manifold nipple, low pressure (turbo inlet) opposite.  Reversing the valve
(easy to do the oriface diam is the same) will allow the valve to "blow" open
sooner, more specifically, prevents the valve from closing soon enough.  Air
DENSITY has nothing to do with bypass valves blowing open, or their
effectiveness to FLOW and PSI.  The valve could care less if the charge air
is -40 degrees or 400 degrees, it "blows" open at x psi.  The stock k24 is
good to around 14-15psi (btdt & Ned tech tip), the sport q uses as stiffer
spring and is good for boost levels in the 18-19psi range (btdt & Beckius).
 There are direct replacement all aluminum ones direct replacements available
that are good to 24psi (btdt).  

A "larger" cold side on a turbo can prove a stock valve ineffective at
dumping enough air FLOW, sending a pressure spike back to the fan, btdt.  The
HKS sequential race valve is a good thing for 2 reasons.  HKS uses a stiffer
spring (raising the amount of boost before leakage) and it uses a larger blow
off area.  Running multiple smaller "stiffer" valves can give the same
effective FLOW and PSI rating as the HKS.  2 of these smaller valves has
proven effective, and the package is mucho smaller and simpler to install.

To the question, yes, most dump the valve outlet to the inlet side (between
air flap and inlet) of the turbo.  This is to keep all measured air closed
loop (archives has a few posts on this), preventing rich fuel spikes if valve
open to atmosphere.  A quick paruse of archives on the Talon Web pages, shows
some empirical data for those who think closed loop turbulence is a factor.
 A couple of guys did tests on this exact theory:  1/4 mile time with valve
hooked up closed loop, then 1/4 mile time valve open loop.  Difference?  .3
sec in the 1/4mile times.  Conclusion:  Ok when racing, but the O2, CAT, and
sound/smell issues make open loop on the street not worthwhile.   

DENSITY is not an applicable term to a by pass valve.  PSI and FLOW are.
  Hope this helps clear this up. 

Scott Justusson
'87 5ktqwRS2
'87 5ktq2GO
'86 5ktqw
'84 Urq