Date: Sat, 15 Jan 2000 14:39:08 -0500
Reply-To: David Beierl <dbeierl@IBM.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@IBM.NET>
Subject: Re: Fast German Auto chip--let's test it!
In-Reply-To: <006701bf5f09$a9c83d40$10e1e1df@marshall>
Content-Type: text/plain; charset="us-ascii"; format=flowed
At 10:36 PM 1/14/00 , Marshall Ruskin wrote:
>Not me - because it's snake oil, IMHO.
Maybe not entirely...
>Digijet/Digifant fuel injectors cannot be "on" for more time than they
>already are on, at full throttle.
I take this to mean "at max rpm." Is this an inference, i.e. it would cost
more in some way to make injectors with excess capacity, therefore they
probably didn't do it -- or do you actually know what the pulse time is at
WOT/max rpm?
>Only improvements possible could come from, as I have said before, higher
>fuel pressure from the fuel pressure regulator, or possibly bigger
>injectors.
Correct at rpm over about 4k.
>And this would have to be done in conjunction with modifying/recalibrating
>the AFM.
Not the AFM, the ECU.
>Because at full throttle - our AFM's are essentially maxed out - and cannot
>meter any more air.
*Not* full throttle -- high rpm. The AFM runs wide open from about
3500-4000 rpm up. Below that speed its action would be affected by the
high-lift rockers. Of course the rockers would cause the AFM to be
wide-open at lower rpm than before.
My conclusion: At mid-rpm where there is plenty of available pulse time,
*and where the maximum torque is available* -- up to around 60 mph in
fourth gear -- the increased air flow from the rockers would cause the AFM
to open wider and the ECU would increase pulse time
proportionately. However, once the AFM is wide open, the ECU shifts to its
internal map, and the engine would run lean unless the lambda compensation
range could adjust for it.
That's where the chip comes in -- the major difference btw it and the stock
chip is that very map. It provides an increased basic pulse time to match
(one hopes) the increased airflow provided by the rockers. That works fine
right up to the point where the injectors are open continously. At that
rpm, whatever it is, you've run out of rope. No more gas going in. It
seems to me there's a fork here: if you're using all the available power
at that point, you simply won't go any faster. But if you're not, the
motor is going to run lean. Will that hurt it? I dunno, need someone who
knows more about motors than I do. The chip could certainly limit the revs
to a lower number than the current 5600 or so. How this all fits together
at high rpm really depends on how much margin the stock injectors
have. Should be easy enough to 'scope one of the injector leads while
someone flogs the beast. Somebody wanna come drive for me? Maybe I can
get my wife to do it. Maybe. Actually somewhere in the flatlands with a
long gentle downgrade is what you need, not readily available here in New
England. Gotta get it up to about 100 mph at full throttle in cold weather
to get worst-case. The cold weather we have, but not the ten-mile slope.
david
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
