RS2 turbocharger

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Dave:
Comments inserted.
In a message dated 6/8/02 11:09:47 AM Central Daylight Time,
quattro-request at audifans.com writes:


>well i'm running an rs2 turbo on my 20v, with higher boost, modified exhaust
>cam, modified airbox, inlet and exhaust manifolds, and exhaust system.  it
>has a larger intercooler, uprated fuel pump, slightly lower compression and
>an uprated motonic, and uses only 98 ron gas.  throttle response and lag are
>still not good, and cannot compare to the 3b w/k24.  great top-end though.
>no, not great, wonderful - far better than the k24.  but around town, even
>many times on the motorway, i'd trade the top-end for the "stomp" of the
>k24 - in the rs2, "stomp" almost always means changing down at least once.

Dave, get rid of the dual mass flywheel.  Life gets better.  Way better, see
your own numbers below.

>i've also had seat time in an uprated rs2 (w/mtm 340hp upgrade) and found
>exactly the same issues, although the top end is better.  i've also had 3
>years in an s2 (3b w/k24) with similar weight as the rs2 - again much better
>throttle response and less lag than the rs2.

Trend:  Flywheels.  Specifically, reciprocating mass.

>i know what the hp charts say, but the reality is that the rs2 is not giving
>serious boost until over 3,000 rpm, 3,200 is "nice", and this is almost
>1,000 rpm higher than the same "boost point" in the k24 ur_q application.
>read any road test of the rs2, or post on the rs2 list, and you will find
>the same comments.

Any folks running the lightened flywheel with the same comments?
Interestingly, the RS2 in the 10vt makes power quickly, and IME reflects the
2-300rpm differential audi "charts".  Which leads me to the conclusion that
reciprocating mass has a large effect on power up.

>charts are one thing, but i believe the stopwatch (courtesy of autocar) - so
>lets compare.

>5th gear in the ur-q is 4% higher than 6th gear in the rs2, yet despite
>this, the 20-40mph time is 9.4s vs 14.8 sec for the rs2.  for the 30-50mph
>time, read 7.1 against 12.5!  even at 50-70mph, the ur_q is faster with 6.5
>against 7.7sec.  so despite a slightly higher gear, the rs2 is on average
>over 50% *slower* than the ur_q - at any legal speed in top gear.

A couple things to think about Dave.  You'd really have to look at the "how"
of this test to "blame" the difference on the turbo.  IF you take the
standard test, which is to go from coast mode to WOT, this is a reciprocating
mass problem.  How can you conclude this?  Well, despite your conclusions
that the RS2 is "40% slower", in straight line acceleration in a variety of
gears, the RS2 is significantly faster 0-60 or 1/4mile.  What's the
difference?  Well, reciprocating mass and bypass valve now eliminate the
spoolup differential.  Which means that anything you can do to reduce
spoolup, makes a huge difference.  FROM your own math (and specific car
examples) presented here that would point directly at the flywheel.

>but what about weight you say?  well, lets look at the heavier s2 (3b
>w/k24).  comparing 4th gear in the s2 with the rs2 in 5th gear (5% higher
>ratio in the s2) yields 20-40 in 5.8s (s2) and 10.4 in the rs2, 30-50 in 6.0
>to 8.4, and 40-60 in 5.4 to 6.3.  so, again, despite a higher ratio, the rs2
>is over 30% slower than the s2.

Again, the RS2 takes the S2 in acceleration (cummulative sum of the above).
You misread:  It's a weight issue, but NOT exclusively chassis weight.  It's
what's hanging onto the flywheel.  You have posted before about wheel and
tire weights.  It's the same principle.

>so the stop watch says to forget the rs2 turbo and get a k24 if you want
>low-end grunt, and minimal lag.

Different conclusion:  The stop watch says dual mass flywheels compromise a
larger turbo's ability to give performance gains over the k24.  If you want
low-end grunt, either get the k24 or lighten the flywheel assembly and grab
the RS2.  According to audis own numbers (and the one's Dave E posted above),
the conclusion hasn't changed:  The RS2 turbo "can" have minimal lag in the
properly tweeked quattro.  Increasing rotational mass sucks the life out of
turbo cars.

>but what the hell would i know?  i don't sell modified turbos for a living
>;-)

Neither do I.  I do know that RS2 turbos can outperform k24's with less than
a 300rpm differential.  I do know that k24 heat soak in a fraction of the
time it takes an RS2 to do the same thing.  K24's are great for short bursts
of power, not sustained runs.  RS2 turbos can run with minimal heat soak at
22psi, the k24 will have your fan on supersonic within a minute at that same
boost level.  BTDT.

Scott Justusson
RS2 and k24 equipped quattros.