No subject

boost  controller on a stock or nearly stock engine. My S4 has only a Hoppen
Stage 1 chip and minor exhaust upgrade, and is using the stock WGFV (yes,
recently replaced as well as the bypass valve, both with oem models). The
boost level will peak at 20psi but fall rapidly to about 12psi if I stay on
the throttle. Isn't this the ECU/Hoppen chip trimming boost due to input
from the various sensors or simply the way it is programmed? Whatever it is,
I think it's desirable with a nearly stock engine, and a puny K24 operating
at 6000ft (remember those pressure ratio charts?). I'm aware of others using
electronic boost controllers to run run consistent boost levels >20psi with
the K24 at this altitude and this sounds like a dangerous situtation! (As a
sidenote, cranking the wastegate adjustment down a few turns on the S4 helps
the boost ramp up  a little quicker.)

Gary Kaklikian
86 4ktq
92 S4
 

> ----------
> From: 	QSHIPQ at aol.com[SMTP:QSHIPQ at aol.com]
> Sent: 	Wednesday, January 31, 2001 4:12 PM
> To: 	quattro at audifans.com
> Subject: 	manual boost controllers, and ECU functions 
> 
> 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)
>