Re: schrick and RS2/S4

[Eliot Lim <eliot@u.washington.edu>]

On Sun, 5 Feb 1995 PDQSHIP@aol.com wrote:

> Agree, but the S4 turbo is designed to give max boost at below 1950, so it
> will certainly peter out sooner than the RS2...  

as i understand it, the S4 develops max. *sustained* torque of 230+ lbft
at 1950 rpm when the turbo is fully spooled.

then there's this overboost feature where the computer will temporarily
raise max. boost to 2.15 bar for 15 seconds.  the torque developed during
this time is 280 lbft and it happens further up the rev scale than 2000 rpm.

i tried this in 2nd gear and before i knew it i was at 7000 rpm...

the s4's wastegate is also electronically controlled.. i don't think
the various IA kits do this, do they?  e.g. it doesn't dump boost when
you are shifting (does it dump boost eventually?) and the entire
torque curve is pretty much determined by the turbo software since it
controls how much boost the engine gets.  i think it is an engineer's
dream to be able to predetermine an engine's output characteristics
then have the necessary hardware and software to *implement* it!
always thought that was neat.

don't forget the distributorless ignition that audi says is important
for high pressure combustion.. apparently with the coils sitting
directly on top of the spark plugs there is more current/voltage that
can be supplied to the plug.

ah, then the 4 valve head should be good for high rpm breathing too,
wouldn't it?

> The RS2 with the mods I
> currently have however is giving me some big boost numbers 1.6 @2300 down low
> with my current setup...  Obviously not getting the full benefits of the 2
> right now but the linear power is certainly higher that any s4 I've driven

i have to admit that i have not tried any tricked out 5K at this
point..  ned's shop is only 1 1/2 hours drive from here.. perhaps i
should go visit him sometime, but there's nothing that he can do for a
v8...
 
> BTW, Ned ritchie has a 280hp setup for the s4 with no turbo mods, but my
> thinking is that with some creative uses of the stock turbo and 272 cam, you
> can get this on the 5ktq.  Where the S4 will always have the immediate
> advantage is in the between shift throttle on, because the boost is bled
> instead of shut off as in the other turbos.

why don't they do this on *all* turbos?  to me it makes the biggest
difference between a driveable and undriveable turbo..  just my
personal opinion.  porsche dropped this feature when they did their
315bhp soup up.. :(

i think ned's 280 bhp mod simply allows the engine to develop 2.15
bars sustained rather than for just 15 seconds.  (i'm guessing here,
but it would seem like a logical first step)
 
the chief mechanic at the dealer here passed on some gossip that
several S4s in idaho and montana (where you have 55mph-unenforced,
deserted autobahns) have suffered broken gearboxes because their
owners ran them flat out for too long.  beware, guys.. the earlier
5KTQ box is apparently bulletproof.  one bonehead owner selected
reverse at 60mph and the box suffered only minor, repairable damage.

i've also been told that the 6 speed audi box can be fitted easily if
the 5 speeder breaks.. since they sell that 6 speed in germany it is
probably a stronger box too.  the dual mass flywheel of the s4 is also
another area of concern.  performance car says that this is the reason
for the 15 second limit on 2.15 bars.  i've seen factory documentation
on the effects of this flywheel.  on the graphs it makes a noticeable
effect on the smoothness of the engine.  it is my impression that the
earlier cars are cruder, but much much tougher.


eliot