RS2 turbocharger

Tue Jun 11 09:23:51 EDT 2002

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Comments inserted.
In a message dated 6/11/02 4:49:43 AM Central Daylight Time,
Dave.Eaton at 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

>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 ;)

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

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