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Re: schrick and RS2/S4

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  I have a question about the statement "not moving more air, but
  maintaining boost".

  Is not the amount of air moved purely a function of the boost pressure,
  all else being equal? In other words, if the S4 turbo can maintain the
  same boost pressure as, for example, the RS2 turbo, at a given RPM, then
  will not both turbos be moving the same amount of air? I should think
  that so long as the smaller S4 turbo can "keep up" with the required flow
  rate, ie the boost pressure does not drop below the WG setting, that the
  S4 and the RS2 turbo would be moving the same amount of air and the
  power/torque output would be equal. If this is all true, then the RS2
  turbo would only have an advantage over the S4 turbo above the RPM level
  that the S4 turbo could no longer maintain max boost due to flow
  limitations, assuming of course that you could spin the engine fast
  enough to have flow limitation with the S4 turbo.



  ========== On Thurs, 2 Feb 1995 - quattro-owner wrote: ==========

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Yes the 272 is the middle cam for the 5cyl:


The 272 with the IA stage 1 computer mods was good for about 20hp.  think
with the S4 the gains are about the same, cuz the S4 turbo strength is not
moving more air, but maintaining boost.  I had this discussion with Ned
last year about the S4 vs Extrud Honing the stock (oversize by race
 It was my opinion that the larger turbo has the advantage of being able to
keep the loaded car (weight)  performance better than a smaller but faster
spooling turbo...  I held off on the S4 for that reason...  Then the boys
at porsche did that RS2 thing and Ned will admit that it is the Cats meow.
The S4 turbo, will however gain some precious seconds in the throttle
response and torque figures (by more boost sooner) and doesn' dump the
boost between shifts, but I am getting 1.8 bar (with the cam timing up one
sprocket) at 3000rpm.



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