manual boost controllers, and ECU functions

[isham-research.freeserve.co.uk at pop.pol.net.uk]

> 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.

Yes, but there isn't much scope in such a system.  A really _noticable_
change requires a stiffer spring.

>>>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.

Three seconds is an effing long time to be alongside an articulated
lorry on a country road waiting for the boost to arrive.  If a stiffer
spring shortens this by only half a second it's worth doing.

> 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.

The WGFV loop runs at about 6Hz.  I agree that its scope is limited and
said so previously.

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

It depends what you want the WGFV to do.  Its design goals are to reduce
turbo lag by programmed overboost and fine tune output by eliminating
some manufacturing tolerances.  It's not intended as a major contributor
to the system.

--
 Phil Payne
 http://www.isham-research.freeserve.co.uk/quattro
 Phone +44 7785 302803   Fax: +44 7785 309674