[torsen] Re: [urq] RE: RS2 turbocharger

QSHIPQ at aol.com QSHIPQ at aol.com
Wed Jun 12 10:21:38 EDT 2002

Comments inserted
In a message dated 6/11/02 6:08:20 PM Central Daylight Time, 
deaton at tranzrail.co.nz writes:

>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.

Thanks for bearing with me.  What I have a really hard time understanding 
Dave, is a motor that has specifications indicating that torque is equal at 
2300rpm, and torque is 40lb/ft higher only 500rpm later (2500).  In my simple 
world, I equate more torque with a cars "ability" to outperform another.  Is 
this not correct?  When I see the type of lag you are posting vs an 
engine/turbo published output, I'm looking at everything BUT the turbo.

>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".

A different summation:  RS2 cars have classic turbo car lag symptoms.  The 
question?  How do we reduce that?  Reduce rotating inertia (Ok Bernie?).  
That would include, those big heavy wheels/tires/brakes the RS2 sports, the 
clutch assembly mass.  You might also consider looking at the OTHER known 
differences:  the intercooler efficiency (larger IC's tend to be less 
efficient at lower PR), even the intake manifold is different, exhaust 
manifold is different, so is the exhaust cam....  The OBVIOUS cummulative 
effect of ALL these issues, is the RS2 can't keep the performance level at 
the EXPECTED/CHARTED 300rpm torque peak differential.  

>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.

I understand your point, I don't agree with it, nor do I come to the same 
conclusions.  The published data on both turbos AND their specific 
applications would indicate that a 300rpm differential exists between the 
equal torque peaks (no argument?).  If that is the case, then what we SHOULD 
see, is a 300rpm differential in PERFORMANCE.  IF that isn't happening, why 
not?  The turbocharger application is the easiest thing to point at, but 
hardly the ONLY thing to be chasing.  My point is, the MAP and the OUTPUTS 
show how close these turbos are.  So I'm just not with "blaming" the 
turbocharger for RS2 shortcomings.

I'm not arguing with the math (yours OR audis), only questioning your 
conclusions of WHY the practical application of the published numbers, 
doesn't correspond with the measured performance. 

IF all what you say is true, than my lowly t44tqw should get smoked by k24 
turbos running 2.1bar and with ligher weight.  Bob Dupree (84 urq with 
optimized k24) and I have tested that many a time on LSD here in Chicago.  
After we laugh about the antics over beers, it sure makes me think it ain't 
the turbo that's a problem.

Tommy Arnberg was recently quoted on the 200q20v list with the following:

>I´ll let you know how the 3B DI engine combo performs. One
>thing is sure that the engine revving sound is
>different in 3B Direct ignition
>than in AAN based vehicles.

>I wondered why and quessworked that the reason
>might be the MUCH heavier flywheel and crank damper
>in AAN ???

>I think that the much lighter 3B
>is much eager or hungrier for revs.  It is like a racing
>flywheel to S4.  - So it seams and the car
>is asking for more REV punishment. More to come later when
>the engine has been driven in next 1000-1500 miles...


Maybe we need to hear from Tommy again?

Scott Justusson
k24 and RS2 equipped quattros

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