[s-cars] Re: Living at altitude - Apexi and turbos

[QSHIPQ at aol.com]

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Kirby, comments inserted
In a message dated 10/4/02 2:32:56 PM Central Daylight Time, kirby.a.smith at ve
rizon.net writes:


>I use the A'pexi mainly to keep first gear boost down to save my tranny.

What's it doing the rest of the time?

>Its not obvious that snappiness implies that I am operating to the left
>of the surge line. If I were, the overall response should be worse.  In
>any case, vehicle acceleration loci on compressor maps tend to start by
>moving to the right.  Normally they bend and end up roughly parallel to
>the surge line; crossing over the line occurs late in the gear, not
>early where the concept of snappiness applies.   Just think of the
>A'pexi as a lower-creep top-control waste-gate controller design.  Isn't
>that what was used on the 5000?

No, not really, WG creep was a function in the 5000 cuz the response wasn't
as good at lower boost levels in terms of the feedback loop.  Crossing over
the surge line can occur in ANY point during the profile (boost vs rpm vs
compressor rpm vs load).  Making the statement that this occurs "early" or
"late" is too general a statement, acctually it's the lower rpm's that can
greaty affect turbo ramp up.  lower rpm surge line indescretions aren't felt,
there just could be better.  Higher rpm surge line indescretions many times
*can* be felt, many times just compared.  When I compared them, I had 2 cars,
1 with controller, one with software.  You could get some "snap" but when you
dialed out the surge, the advantage went to motronic.  As a point of
reference my tests were performed in 3rd gear, not first.

>I see no fundimental functional difference between a frequency valve and
>a stepper motor.  Either can regulate the flow of control air, and I
>estimate that a frequency valve can do so with better bandwidth.

I would say it would depend on the hardware.  The stepper motor in my Profec
B is accurate to tenths of a psi on my 4runner.  The WGFV in audi turbo cars,
tends to be accurate to a couple of psi depending on how hard you whacked it
and how many times.

>  I
>doubt that there is anything that can happen to the turbo state in less
>time than the A'pexi can react, although something might occur faster
>than the WG can react, but in that case even the OEM design cannot do
>any better.

Well, in the case of surge line for instance, better isn't faster
necessarily, in fact....  Right now you have boost vs rpm on the apexi.  What
about charge air, engine temps, knock, or altitude?  The boost controller
doesn't know the difference, cuz it can't.  Motronic does.

>You may argue that neither the A'pexi valve or the OEM
>valve are large enough for some applications, but that is a different
>issue.

I only argue that you must see motronic ECU as three interconnected
controllers.  Motronic is a fuel controller, a timing controller, AND a boost
controller.  As a boost controller, it's better than the most sophisticated
on the market.  AND (bonus) you already have it in your car.  The hardware
it's hooked up to (WGFV itself) sucks in stock trim.  Adding 200hp to that
equation isn't going to make things better.  I advocate you fix it instead of
taking away it's excellent integrated function.  Fix what's busted, don't bag
it and buy something else - every audi owner should know this creed well.

My .02

Scott Justusson