[s-cars] Re: wrt pushing RS2 to the edge...

[QSHIPQ at aol.com]

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Whew, didn't know which to pick, till I saw this one.  I'm with Calvin and
MLP here.  Minhea, first off, a dyno is a great tool for a single run.  IME,
with many comical hours with imported 3phase fans on high and plant sprayers
(even CO2, and a variety of fridgedly 'Icey cocktails") in hand, Calvin is on
the money.  If you want to see what's happening in the "continuous world" of
boost, try logging pre and post IC temps and pressures.  For simplicity of
argument I just chose the RS2 full metal jacketted regalia 90% of the S car
boys do as "upgrades".

 Remember too, with any turbo there is a maximum boost/hp level, and a
continuous boost/hp level.  As we further any discussion, we should
differentiate the two.  In maximum boost levels, Frank ran over 30 (before
some batboy whacked him), and another lister ran over 30 too, whom I also
whacked in a public fashion years ago.  He wasn't as lucky as Frank.
Personally, for momentary boost levels, I've been witness to numbers that
defy belief on many audi turbo quattros (even 1.8t).  I've also seen several
cars grenade themselves at their very first track event with those exact same
levels they ran for years on the street.  IMO, I would point you to Calvins
formula for the exact reasons why.  And I would take exception somewhat to
20Nm being huge (if anything at all, I've seen that difference in two runs
with the same plant sprayer), in fact, in a 5 minute drive, or <2minutes on
track, that could become nothing, or less, btmt

You can dial a lot of things thru "chip" tuning, but heat soak is tough, even
for the "good/proper ones".  IME2, finding a turbo that will blow 2.8>PR at
good efficiency really isn't applicable to an I5 2.3L motor (save
specifically only the RS2 turbo, but read more below).  Given the formula
below Calvin shared, something has to change, specifically one of the
variables has to change.  What are you doing in the programming to decrease T
in the boost equation?  But specific to your argument Minhea, if you look
strictly at the RS2 Map itself, your "peak" hp/torque levels at 2.8PR (turbo
spinning at 135,00+rpm) vs 2.4PR at 120,000rpm, which will heat soak first?
If you look at it harder, you will see that the output (volume) can be the
same 400cfm for both PR at the same compressor efficiency of 72%.  Why more
pressure?  Isn't this really an indication of a Density Ratio problem?

I'm also with MLP...  At Steamboat's expensive Bagel-fest parking lot get
together earlier this year, lot's of discussion with MLP regarding that
intake manifold you guys are using, specifically, can it really ram all that
air down the throat of that motor?  I think it will to a point (which I'm
putting forth at about 400RWHP), then more pressure is, well, more pressure.
In fact, it can become so unstable (since it doesn't really have anywhere
else to go) that surging, on both sides of the combustion chamber and both
sides of the turbo, can get really ugly.

I'm a fan of education AND btdt.  I look at the btdt guys for some background
too.  If what you are doing is taking the "I ran/run/program this with no
problems" routine, I'm investing in 20vt motors now....  If what you are
doing is advocating a more complete understanding the principles of
turbocharging and heating charge air, then I argue you aren't running
28psi...  Either.

In absolute full race regalia audisport liked 2.6PR, and when they were
really close to a competitor and wanted to win,  2.8PR with the expressed
permission of AS management based on the exact conditions at the time of the
request.  Messing with 2.8PR in a street car?  Ok, I guess my library and
btdt makes me a bit more conservative than youze guize.

I'd also suggest Minhea, that if we want to "nerd" on pressure, that we speak
strictly in terms of Pressure Ratio, not "psi".  Since PR applies to
turbcharging anyhow, and we must keep our boys in the CO mafia from false
pretenses.

Scott "T not P" Justusson
QSHIPQ Performance Tuning


In a message dated 5/10/2003 12:13:25 PM Central Daylight Time,
calvinlc at earthlink.net writes:

Mihnea,

You say more boost=more torque.  Yes, if you discount heat.  What we are
really interested in here is n in the old equation PV=nRT.  So you can
increase cubes, pressure, or decrease temp.  What doesn't gain you anything
is increasing pressure and temperature from a heat soaked IC at the same
time.  I am sure you meant boost = torque WHEN the temp. stays the same,
right?  I think what some people are arguing here is that you might be
peeing in the wind with the extra 2-4psi because the rest of the system
can't handle it efficiently from either a flow perspective or a heat
perspective.  I don't know.  I run a stock S4 so I have no experience at 28
psi boost levels with these particular cars, but I am 100% sure there is a
point where more boost does not equal more torque because of the
aforementioned circumstances.

--Calvin