[torsen] RE: RS2 turbocharger

[David Eaton]

excellent summary robert and i agree totally.  i love the top-end of the
rs2, and the way that it goes all the way to 7k rpm, which is a point that i
rarely, if ever, take the k24.  and i agree with you that the rs2 doesn't
start "cooking" until over 3k rpms.

btw, i have used 6th gear times simply for the sake of comparison, as the
original question was to do with the lag of the rs2.  14 seconds to go from
20-40mph in an rs2 is something you will only do once.  however, even when
in the 2k range, the rs2 is not optimal and doesn't give anything like the
throttle response of a k24 unit.

my original point is that people who go the rs2 route, as you have, should
not expect that it will behave like the k24 at low engine speeds - because
it won't.

i also think that it is worth pointing out that i don't believe the torque
charts that i obtained and circulated represent every-day reality.  these
came from the owners manuals for my cars.  i would make a distinction as to
how the torque figures are derived.  i believe that the numbers are obtained
while running the turbo "down", rather than up.  when you run the turbo "up"
you are taking spool-up time/latency, as you suggest, into account.  taking
spool-up time into account, there is no way, ime, that the k24 peaks at
1950rpm, for example, and no way that the rs2 performs better than the k24
at 2300rpm as the charts suggest.

dave
'95 rs2
'90 ur-q
		-----Original Message-----
		From:	Robert Pastore [mailto:rpastore at animalfeeds.com]
		Sent:	Thursday, 13 June 2002 2:03 a.m.
		To:	'David Eaton'; 'Quattro List'
		Cc:	'urq at audifans.com'; 'torsen at audifans.com'
		Subject:	RE: [torsen] RE: RS2 turbocharger

		Dave:
		This is a great topic, so I hope we can keep the thread on
track, and not
		veer off into a flame war.

		I have 2 s6's and previously had an Urs4.  My brother still
has a Urs4 with
		k24/stage 1+ that I drive often.   With my Avant, I've gone
through the
		typical rs2 upgrade path(
software/injectors/MAF/EM/Turbo/Exhaust cam), and
		now also have a 10.6lb aluminum flywheel.  I track the car
often.  FWIW,
		here's my opinion/experience.  Sorry, but I have no
engineering equations,
		numerical data, Reynolds numbers, or pi-r-squared. I just
have  daily
		experience both commuting and on the track.

		1) There is no doubt the rs2 has a boost onset that is later
than the k24.
		The crossover point is around 3,000 rpm.  Above that, the
rs2 has a huge
		advantage over the k24.  The k24 feels out of breath around
5,800 rpm, while
		the rs2 keeps pulling harder all the way to the rev limiter.
		2) I haven't tried to verify or punch holes in the numbers
you present, but
		I think the whole exercise misses one very important point:

		WITH AN RS2 EQUIPPED CAR, THE DRIVER NATURALLY ADJUSTS HIS
SHIFT POINTS TO
		ALWAYS KEEP THE ENGINE IN THE POWER BAND.

		No one in their right mind would put EITHER car in 6th gear
at 20mph and run
		a race that way.  I'll take that a step further and state
that I don't think
		there is anyone on this list who purchased their UrS to win
drag races.   So
		I think the question becomes, "Who cares which setup is
stronger at low
		rpm's?"

		3) Scott's point on the compressor maps being almost
identical at low flow
		is true, except that the k24 is turning a much higher rpm at
an given flow
		point.    What this neglects however is that hot side that
drives the
		compressor, and with its bigger hot side and thicker
(STRONGER) stronger
		shaft, the rs2 takes hot side has more mass thus more
inertia and takes
		longer to spool.  So it takes more energy and more time to
get the rs2 to
		the same PR as the K24 at low flow rate.  The rs2 exducer
outlet is larger
		(think of this as a throttle for the exhaust), thus the
engine can breathe a
		lot better in the upper rpm band with the rs2.

		Daily driving impressions:

		1) I often trade cars with my brother for a few days at a
time.   The first
		thing I realize is that I am deluding myself into thinking I
haven't lost
		low rpm torque with the rs2 turbo.   There is a lot more low
rpm with the
		K24, and it is immensely enjoyable for the first few hours (
when you are
		still mashing the throttle hard still driving with your RS2
habits).
		However, after about a day of this amusement, I badly miss
the huge upper
		end the rs2 setup provides, and can't wait to get my car
back.   The
		sacrifice at low rpms, considering how seldom I am caught
there when I want
		the power, is miniscule compared to the increased power that
is available.



		Track impressions:

		1) My car is pretty quick at the track.  (In fact the car
makes me look like
		I'm a better driver than I am...I really like that.)   K24
equipped cars
		can't stay close to me on a straight, and have no advantage
coming out of a
		turn because I simply keep the rpms from falling below 3000.
It's not like
		it's work to do this, it is the natural thing to do.

		2) I recently installed a 10.6 lb aluminum flywheel
replacing the 26 lb
		dual-mass stock unit.   The engine revs a lot quicker.  I've
run two track
		events since the change, and at both events I thought I had
an intermittent
		miss and when I hooked up vagcom after the run, found I had
bounced off the
		rev limiter (told you I wasn't such a great driver!).  I
never did this
		before the flywheel install and attribute it to the faster
revving that I am
		really enjoying.  I got my flywheel from Northern European
Performance in
		NH, but I have to agree with Scott that this is a great
modification if you
		are going to drive the car hard.

		Finally, I've found that the right software is a HUGE
variable in the way
		the car makes power and the way the turbo spools.  MTM 1+
does a real good
		job of getting the k24 spinning early, but the typical rs2
offerings from
		Hoppen/IA/Tap etc do not do the same for the rs2. I do not
see the rs2 as
		having much lag
		at all, but it certainly has a boost threshold that is
several hundred rpm
		later than the stock k24.

		Bob

		-----Original Message-----
		From: David Eaton [mailto:deaton at tranzrail.co.nz]
		Sent: Tuesday, June 11, 2002 7:09 PM
		To: 'Quattro List'
		Cc: 'urq at audifans.com'; 'torsen at audifans.com'
		Subject: [torsen] RE: RS2 turbocharger


		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.