Re: Compressor bypass valve questions...

[QSHIPQ@aol.com]

In a message dated 97-10-19 11:29:51 EDT, you write:

<< 	I would admit that my 5KCSTQ's engine responds _alot_ quicker 
> than a CIS-equipped engine, but I find that on my car, with the Redline 
> in the transmission, and a well lubed shift linkage, I can shift pretty 
> quickly, and my boost doesn't drop much at all between shifts.   Maybe a 
> couple tenths of a second wait to get back up to full boost.   If that 
> were cut in half, that would be barely noticeable on a quarter mile run I 
> think.   This definitely falls into the "last tenth" category IMHO.   
> Especially with the small bore bypass valve that is typically used.   If 
 >it were a 2" bore (or more) that flowed air _very_ smoothly, I would be 
 >more anxious to try it out.
  >>
Running 2 or more would solve the problem me thinks.  Regardless on how fast
you shift, you will eventually wish you had done the job, it only takes
one...  Something like a kid rides his bike in front of you whilst you are at
full bore for instance.  Running high boost and closing throttles doesn't mix
well.  I measured over 50psi pressure spike (Ned claims 70+ is realistic)
with a stock k26 running a stage II mod.  Where does that go?  Well, right at
the blades of a spinning turbo, in fact.  What is referred to as turbo stall.
 This puts a huge load on the turbo bearings and the wheel itself.  All the
valve is doing is allowing the turbo to freewheel, or in the case of really
high boost, at least massively reduce the pressure spike on the IC and turbo
wheel/bearings.  Performance?  Doubt it gives a whole lot, especially if you
use graydon's shift method.  Some get a mild increase in performance, which I
stress is mild, because a freewheeling turbo takes less time to spool boost
than a non freewheeling turbo.  I personally don't see a bypass valve as a
performance gain, only a preventive maintenance item.  Saving turbos and IC
end caps is a good idea, especially as you approach and exceed 1 bar boost
pressures (14psi +).

Late 87 44 chassis turbos use a delay shut diaphram on the t-body (on the WOT
side), which is a big help, especially combined with the valve.  The bigger
the turbo one uses, the more key the bypass valve becomes in the equation.
 BTDT.   Just about every turbo car built since 1989 uses one, from a audi to
Talon, from Probe turbo to S4.  There are some good discussions in the
archives of the Talon list on bypass valve as well. 

Scott
'87 5ktqwRS2
'87 5ktq
'86 5ktqw
'84 Urq