manual boost controllers, and ECU functions

[QSHIPQ at aol.com]

Phil Payne writes:
>>No.  All 'chipping' mods are accompanied by replacement wastegate
>>springs.  This is what actually does most of the work.  'Chipping' is
>>done in a number of ways including simply disabling the overboost
>>cutoff, moving the point at which it occurs with a resistor bridge,
>>doing this in a slightly more sophisticated way with a zener diode, or
>>full remapping.

Be careful here Phil, all chipping mods aren't accompianied by replacement 
springs.  The zener mod doesn't 'need' them either.  The springs are more a 
function of the slow feedback loop and airflow limitation of the WGFV's found 
in audis.  Wastegate cracking is specifically what's happening.  For more, 
get Maximum Boost from Corky Bell.   If you had a stepper motor from a manual 
boost controller, you could use the stock spring or less with better results. 
 

>>A chipped ECU reaches target boost slower than an unchipped one - the
>>inertia of the turbo is unchanged and it has to spin up further.  The
>>stiffer spring means you reach the previous maximum more quickly, but
>>it takes a little while longer to get to the top.

No.  The reason a chipped ecu reaches boost sooner or later has *nothing* to 
do with the turbo, a turbo can overboost within 3 seconds quite easily.  
Again, the reason target boost is slower is that the WGFV loop is slow and 
can't overcome wastegate cracking easily.  To test this, get a stock spring 
(or weaker), just add a line to the top of the wastegate from the manifold, 
you can have unlimited boost faster than any "unchipped, chipped, zenered," 
turbo car.  The reason for the stiffer spring is that the airflow and 
feedback lookp of the WGFV can only really add 2-4psi on top of spring 
pressure.  Again, compare this to an external boost controller with a stepper 
motor, the limitations of the audi system is obvious, whether speaking of the 
top feed early WGFV function or the bottom feed later style WGFV's  The early 
ones are slow, the later ones leak, so stiffer springs on both make for 
better turbo response.  

IMO, you shouldn't blame the turbo for the crappy audi WGFV function.  For 
purely boost function aftermarket controllers are better than audis. 

HTH
Scott Justusson
'87 5ktqw (2.5bar with 1.8bar spring)
'83 URQ (2.2bar with 2.2bar spring)