[s-cars] '93 UrS dyno results

[Robert Pastore]

Frank:

I lost a bet with John Petersen on this one, I was in the same camp as
you!!!  I had a long discussion with the guys at RC engineering, and they
said the fuel injector flow is based on the pressure differential at the
orifice.    As you add boost pressure on both sides, the delta remains
constant, and so does your fuel delivery for a given injector duration.

Frank, I think an adjustable fuel pressure regulator is a crude way to try
and solve a lack of fuel at high rpm and high load.   It should be in your
tool basket, but probably not the first thing you want to try to solve the
problem.

I would first make sure I had a chipset that was designed for horsepower you
are trying to achieve, and then match the HW to the HW assumed by the SW.
The Hoppen/Lehmann chipset you have was designed to run rs2 HW in an AAN
ECU.  Although many have this chipset straight form the source with only rs2
turbo and WM, the resulting HP of this setup is IMO disappointing because
you cannot deliver enough fuel to support the higher air demand and PR's the
rs2 can support efficiently in roughly the 4,000-5,500 rpm range.  From the
rs2 compressor map on Mockry's site, look at the high PR's it can support,
then calculate the AAN air demand.   Once you put a WOT air/fuel ratio to
the air demand, you know fuel needed, and if you could look inside the chip
at the injector duration, the product of the duration, fuel pressure, and
stock injector flow rating leaves you short of fuel to exploit the potential
of the rs2 turbo.
Most of these calculations can be done with java calculators available at
the Ray Hall turbo charging website.

Aside from the math, I've driven or ridden in s6's that have had this
chipset both with and without the rs2 MAF & injectors.  The difference is
huge.  I am not sure that Hoppen has given or has all the information about
what HW this chip was designed for.

Of all the chipsets I have, I only have 2 timing chips that are specifically
for rs2 HW in an AAN ecu.  I've spent a lot of time trying different HW
combinations with these two chips, and they both run best with the following
HW:

rs2 turbo
rs2 EM
rs2 FI
rs2 MAF
AAN FPR
rs2 cam -- optional

I have the rs2 fpr and have tried it with both and get high load light rpm
lean conditions/misfire.  I've got no experience with the effects of
altitude on these findings --- I am at sea level.  Before trying adjustable
fpr, see if you can borrow FI and MAF, then try again.   The install time
for both is under an hour, and I think you'll find that 50 HP you are
missing.

Finally, if you do decide to go with an adjustable FPR, use a fuel pressure
gauge under the hood.   I had some double banjo bolts made so you could pull
fuel pressure off of the banjo fitting at the front of the fuel filter.   I
think these cost me around $15 each.  Let me know if you need one.

Bob

-----Original Message-----
From: fjamoroso at webtv.net [mailto:fjamoroso at webtv.net]
Sent: Tuesday, October 01, 2002 8:23 AM
To: CaptMagu at aol.com
Cc: s-car-list at audifans.com
Subject: Re: [s-cars] '93 UrS dyno results


Thanks Hap,

Forgot to mention that I too have the RS2 cam. Time to play with fuel
pressures.

Some time back we were all discussing the stock FPR, and if boost
pressure was added to the value stamped on the unit. I seem to recall
someone being pretty adamant that this was not the case (i.e. the stock
system is not rising rate, even though it seems would be with the vacuum
/ boost line adding pressure to the top chamber of the FPR), Can anyone
refresh my memory here?

Frank at s-cars.org

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