[s-cars] RE:Wastegate spring tightening

[Mihnea Cotet]

Pizzo, thanks for the input. My point is that these limits (boost and 
timing limits) depend on the backpressure generated by the exhaust. If the 
EM/turbo hot side/DP/exhaust are too small and acting as bottlenecks in 
terms of flow, thus if they produce high backpressure, it's gonna be good 
for getting high boost at low RPMs, but it's also gonna be a great way of 
getting pinging at the top end, which will automatically limit the power. 
All this is aside from all cold side efficiency considerations, if the 
turbo runs at 250k RPM and 0% efficiency with 28psi at the redline (the RS2 
isn't far from that with that much boost but it's just an example), then 
it's totally pointless to even consider running that much boost, nevermind 
your turbo won't even last for a couple of hours.

The key word is back pressure. The more back pressure, the more efforts the 
engine has to make to get the gasses out (pump losses for the MEs out 
there), which means lower knock threshold, higher EGTs, higher heat 
transfer from the hot side to the cold side, yadda yadda yadda, i.e. less 
overall power and more risks involved in ruining the engine.


HTH,

Mihnea

At 08:31 15/10/2004 -0400, Joe Pizzimenti wrote:
> From the other side of the world...
>
>I've found in tooning my own car, even though the Evo has a lower
>compression ratio (8.8:1 vs. 9.3:1), on pump gas the limit seems to be
>22psi before timing starts to get pulled back due to detonation.  Ask
>around and most other tuners will tell you the same thing.  Unless the
>timing advance is really, well, retarded, running high boost on pump
>gas is a great way to remove your cylinder head without lifting a
>wrench.
>
>Personally, I think there's more to be gained with moderate boost
>levels and good timing advance rather than the other way around.
>
>FWIW, YMMV, etc.
>
>Joe, I'm not a real tooner, but I play one on the Internet, Pizzo
>
>
>
>
>On Fri, 15 Oct 2004 14:16:31 +0200, Mihnea Cotet
><mihnea.cotet at easynet.be> wrote:
> > Guys,
> >
> > Just a little info here: 28 psi all the way to 6k RPM and 25 psi up to the
> > redline are both "suicidal" boost levels for an RS2 turbo.
> >
> > Apart from being bad on the turbo itself (overspinning at high RPMs), it's
> > also totally unefficient and turns the turbo into a large heat pump.
> > Efficiency must be close to 40% at these sort of boost levels and such high
> > RPMs. Which means that your cars will be making lots of power at relatively
> > low RPMs (4k to 4.5k) and then the power will simply tail off, because of
> > the increase in heat on the intake side, and also because of the stupidly
> > high backpressure levels in the exhaust, which in turn makes the engines
> > ping a lot easier, so the ECUs will dial the timing advance back to keep
> > the engines from knocking.
> >
> > Together with my german tuner colleagues, we have a phrase to sum all this
> > up: manchmal ist weniger mehr, or in english: sometimes less is more.
> >
> > Just a thought...
> >
> > HTH,
> >
> > Mihnea
> >
> >
> >
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