[s-cars] RE:Wastegate spring tightening

[Mihnea Cotet]

Scott, good to hear again from you after such a long time. see my comments 
inserted below....

At 17:24 15/10/2004 -0400, QSHIPQ at aol.com wrote:
>Minhea:
>I'm confused when I read your two posts vs the RS2 turbo map itself.  The 
>RS2 is quite capable of 25psi (I prefer Pressure Ratios myself = 2.7PR), 
>and in fact isn't a heat pump at that output, it's actually quite 
>efficient (like 73%) at that pressure.  The turbo MAP also indicates that 
>at 2.7PR turbo speed is a relatively safe (albeit close to max) 
>140,000rpm, not double that. Are you sure you aren't referencing a k24 
>turbo here?

Scott, in my first post, I was talking about 28 psi (3.0 PR) at 6000 RPM 
and 25 psi (2.7PR) at the redline (7000 RPM). Plot the engine flow values 
on the compressor map assuming 85% VE for 6k RPM and 80% VE for 7k RPM (I 
quite frankly don't think a standard 20vt has more efficiency than that, 
even the RS2) and see the results for yourself. If I remember my 
calculations correctly, both of them will either be outside the compressor 
map or at very critical points in that map. And again, I'm talking about 
the 2672 cold side, not the 2470 cold side used on the standard 20vt K24 
turbocharger.


>Pipe diameter could be argued as a contributing factor, but the design of 
>the RS2 may offset that somewhat with a revised (less restrictive) wheel 
>design.  Ultimately pipe diameter is a mathmatical reality, but a large 
>factor is the spinning turbine you design into it.

The RS2 turbine wheel is a very good one, but it's not ideal IMHO. Perfect 
for anything below 380 real crank HP, but no good for anything above 
that... This is based off of first hand experience, not hearsay or other 
people's experience BTW.

>All that said, the RS2 is a relatively small turbine (for high HP AND high 
>torque), so heat soak will eventually cause either CAT boost reduction, or 
>knock boost reduction.  I suspect most that see a reduction in boost based 
>on CAT, since knock interventon, IMO, tends to be a bit more dramatic a change.

First off, there's no such thing as knock boost reduction on an I5 20vt and 
it's associated M2.3 (3B) and M2.3.2 Motronic system. There's only intake 
temp boost reduction and timing reduction, but absolutely NO knock boost 
correction. Knock boost correction was first introduced on the M3.8 system 
used on the very first 1.8Ts, as well as M5.9 used on pre DBW 1.8Ts, then 
got to what I consider as a real state of the art perfection on ME7 drive 
by wire system used in all current 1.8Ts and 2.7Ts, as well as any other 
Audi gasoline engine using drive by wire. M2.3.x has never used the knock 
sensors to correct boost, nor is there a way to use them in order to do so. 
Even when an engine is pinging like a churchbell (meaning audibly), and the 
ECU is trying to do its best to retard the timing, boost is never dropped a 
single psi compared to what it is when no pinging occurs. I am 100% sure of 
these statements as I've been able to verify them by myself intentionally, 
on my own engine.

>Exhaust manifold pressures are usually a function of the design of the 
>Nozzles and throat ratios, not so much the backpressure of the 
>turbocharger hot side.  I'd certainly propose that if one is using the RS2 
>exhaust manifold, the RS2 turbocharger unit probably isn't the 
>restriction...  Yet.

Well, no, the RS2 hot side isn't the biggest restriction, but a slightly 
larger hotside will still allow one to get a few more HP from the excellent 
2672 RS2 cold side. I know how to monitor knock sensor activity on an 
M2.3.x ECU and how to figure out when it's starting to retard timing only a 
couple of degrees on one or 2 cylinders at a time, and I've been able to do 
extensive tests with a full RS2 spec turbo, as well as a straight K26#6 hot 
side-equipped RS2 cold side. Running the same boost levels (except at 
pre-3500 RPM where the straight K26#6 hot side doesn't really shine) on the 
same car, there's *up to* 5 degrees more timing that can be programmed 
before the ECU starts pulling back the advance across the whole rev range, 
with the same or even slightly leaner mixtures on the K26 hot side turbo. 
This means about 5-10 crank HP above what an RS2 turbo can deliver with no 
pinging and any action from the ECU to retard the timing, again, even if 
only on one cylinder.

>However, drop an RS2 turbocharger onto a audisport manifold or a tubular 
>manifold, you could easily argue the point.

Hehe, yup, totally agreed, but a better manifold will also free up a couple 
more HP from the same turbo.

HTH and my .02 as well,

Mihnea







>In a message dated 10/15/2004 8:50:48 AM Eastern Daylight Time, Mihnea 
>Cotet <mihnea.cotet at easynet.be> writes:
>
> >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