[s-cars] Bypass valves - Which one?

[QSHIPQ at aol.com]

My .02?  Big compressors can make huge flows with big HP at WOT.  Big 
compressors can make huge flows and surging with less than WOT.  As I shared with 
Mike and Scott D at Steamboat last year, you can do one or both of two things.  
First, you can bypass that air out a valve on the intake side (pre tbody).  The 
problem with this is it doesn't really address the problem, which is ON 
boost, albeit moderate, or attempts thereof.  And, really big turbos don't loose 
efficiency with "leaks" on small motors, so this could be an option, especially 
on a 128ci motor.

The related second problem, more likely the cause, is the lack of enough 
valve area on the exhaust relief side (read wastegate) to properly regulate a 
large turbo ramping up with relatively low exhaust energy input (read less than 
WOT) for the size of the turbo.  This isn't a new phenomenon, audisport was 
dealing with it back in the 80's.  The real problem becomes the ability of 
software/hardware combinations that will allow part throttle on boost situations from 
manifesting themselves similar to being "on and off turbo" like being "on and 
off cam".

Personally, I doubt a good solution will be found in the software hardware 
control, short of putting more displacement into the motor itself.  

My baseline argument is that you want the smallest turbo to do the job for a 
given motor.  Big turbos make massive HP at WOT and RPM, it's a volumetric 
efficiency thing.  When you try to tackle less than massive HP at less than WOT 
and less VE at a lower RPM, you may find that the turbo that was good for the 
ulitmate number, may fall flat on it's face in less than full battle loading.

I would also venture that whatever the "best" solution is, will be confirmed 
on the dyno in terms of the curve.  Instead of using the dyno to whack the top 
end, why not use it to figure out what's happening under that?  My suspicion 
is that you might find the problem at part throttle by looking at the 
torque/HP comparos vs WFO.  

It might also be time to get these Hapersized magical mongo turbos put on a 
turbo dyno.  It's not cheap, but I think the conclusion might become more 
obvious wrt the problem.

HTH

Scott Justusson
QSHIPQ Performance Tuning


In a message dated 12/4/2003 9:51:58 AM Central Standard Time, 
mlped at qwest.net writes:
Hap remains in the hunt for a solution.  With out a running car capable of
pushing the kind of boost that seems to generate the surge, I have some
modified parts to play with, but nothing to check the results on.  So, in
the interim I'm stuck with bad pilot jokes: