RS2 turbocharger

[David Eaton]

you mention "maths" but you haven't posted any.  this isn't rocket science,
and it isn't hard, so i cannot understand your difficulty in coming to terms
with this.

lets look at the maths from the stopwatch numbers.  take the k24 aby s2 vs
the rs2 in top (6th) gear, and the in-gear increments.  time in seconds, rs2
1st, then s2.  using the gear ratios (specifically speed/1000 rpm figures) i
have derived the engine speed at the mph range for each car - which is in
brackets after the time in seconds.

Mph     rs2    s2     rpm range        outcome
20-40  14.8  11.1  (813 to 1626)    rs2 33% slower
30-50  12.5    8.9  (1220 to 2033)  rs2 40% slower
40-60  10.2    7.0  (1626 to 2439)  rs2 46% slower
50-70   7.7     6.1  (2033 to 2846)  rs2 26% slower
60-80   6.0     6.4  (2439 to 3252)  rs2   6% faster
70-90   6.1     6.8  (2846 to 3659)  rs2 10% faster

it is quite clear from this table that the rs2 is not providing useful boost
(and acceleration) to the car until the turbo is spinning over 2,500 rpm.
you can also see that the k24 is spooling up more rapidly (30-60mph
numbers).  the rs2 turbo is only providing better acceleration to the avant
when operating over 3,000 rpms.  a close look at the numbers (particularly
the 50-70 vs the 60-80) also indicates the steep ramp-up in the rs2 turbo
performance.  this again is what your butt tells you when you are driving
the car.  it is the classic definition of "turbo lag".

once again, these are cars with the same flywheels (that nasty old dual mass
flywheel) & transmissions, and very similar weight.  i don't see how you can
come to any other conclusion other than that the k24 turbo is responsible
for the much better performance of the s2 at low engine speeds, over the
rs2.  which was my 1 and only original point.

dave
'95 rs2
'90 ur-q
		-----Original Message-----
		From: QSHIPQ at aol.com
		Date: Tue, 11 Jun 2002 08:23:51 EDT
		Subject: RE: RS2 turbocharger
		To: quattro at audifans.com
		Cc: urq at audifans.com, torsen at audifans.com

		--
		[ Picked text/plain from multipart/alternative ]
		Dave:
		Comments inserted.
		In a message dated 6/11/02 4:49:43 AM Central Daylight Time,
		Dave.Eaton at clear.net.nz writes:


		>scott, do you seriously expect people to accept that the
difference in speed
		>between the rs2 and the 20v ur_q (or the s2) at low revs is
due to the use
		>of a dual mass flywheel in the rs2?  i'm talking the over 5
seconds of
		>difference (in equivalent gearing) going from 20-40mph, and
over 4 seconds
		>going from 30-50mph, (again in equivalent gearing)....

		Dave, the problem is in the "rest" of the numbers....
First, the RS2 motor
		develops 295lb/ft of torque at 2500rpm and holds it there
thru 4600 (your
		numbers here, I presume them to be correct?).  The k24 S4
(your "overboost"
		example) develops a peak torque of 258lb/ft of torque at
1950, and holds it
		there for 500rpm, then it drops quickly.  Which means that
by 2300rpm, the
		ADU motor out-torques the AAN.  350rpm v torque
differential.  Second, the
		turbo MAPS indicate that the airflow "output" of both turbos
is almost exact
		up to the S4 2.1PR (overboost) peak.  All this indicates to
me, that
		somewhere along the line (your actual road test numbers),
the RS2 makes the
		power, but somehow it doesn't get to the ground as
"efficiently".  THAT sir,
		is my only claim.  I'm a big fan of reducing reciprocating
mass, how
		convenient that audi makes that easy to do effectively.

		>i'd like to know where you get your understanding of
physics from...

		Let's look at torque, HP, or a turbo MAP, all of these
indicate that the
		"turbo" isn't the cause nor the problem.  It's not physics,
it's math.  One
		needs to look hard at how a motor/turbo with 40lb/ft of
torque 500rpm later,
		can't get close road performance.  Physics of the two turbo
MAPS would
		dictate that pointing at the turbocharger unit doesn't
appear to be a valid
		argument.

		>if you are so certain that this is the "problem", i'd
encourage you to look
		>at the late model s2, also with a dual mass flywheel.  i'd
be happy to quote
		>the relevant in-gear times, where, due to the overboost
available with the
		>k24, it is noticeably better than the older s2, and so it
just makes the
		>comparison against the rs2 worse.  the s2 (w/aby k24) is a
far far better
		>machine at low engine speeds than the rs2 (and the s2).

		Dave.  Something doesn't add up here, that's all.  Turbo
outputs are
		virtually identical up to the peak of the k24, RS2 motor
torque output is the
		same as the "overboost k24" at 2300rpm,  40ft/lbs more by
2500rpm.

		You "want" to blame it on the turbo.  I look at the turbo
MAP and the motor
		output, and say that doesn't appear to be a valid argument.
Something "sucks
		wind" in the RS2, no question.  A flaw in your logic, is
blaming performance
		shortcomings on the RS2 turbocharger unit.

		I'm confused with the logic you present here Dave.  I accept
your numbers,
		the methodogy, and the published KKK MAPS.  I'm not coming
to the same
		conclusions with the same information (history repeats
itself:).  All your
		numbers sure indicate that the RS2 motor in the RS2 car
doesn't take
		advantage of the I5 performance increases.  Maybe then,
someone needs to put
		the RS2 motor in the urq.  Hey, ok ;)

		SJ
		'84 20vt RS2URQ project
		'83 10vt urq mit k24
		'87 10vt t44qw mit RS2 turbo