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Maximum efficient boost level on an S3 is 1.45-1.5 Bar tops
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On standard ICs...it's probably less than that...and that's just at peak boost.
The S3 ICs are awful...they heat soak and aren't efficient.
With correctly set up ICs you can run higher boost to gain torque.
I regularly ran 1.85-1.89 bar...
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It is your wee turbo that is becoming inefficient that will stop you going higher. Any higher and your back pressure will be really bad -
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Back pressure where exactly, Doug?
Back pressure in the exhaust manifold / cats / exhaust...perhaps.
Possible back pressure in the metal pipe from the turbo outlet to the first SMIC, because of the restrictor / silencer installed in the 'bump' part...maybe. But that's no cause for concern on Davids S3...it doesn't exist anymore!
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running anything above 2.8 PR on that turbo, i.e. anything above 1.6 Bar makes the turbo surge which means that basically it can't fill the engine with the air flow it's putting out and the air flow is coming back into the blades of the turbo making it
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I disagree...
I spend my working life setting up and calibrating industrial compressor control systems...and I'm fully aware of what compressor surge or stall sounds like, once you've heard it, you never forget it!!
...and running 1.8 bar on my S3 didn't cause surge, I can assure you.
I can see that you may get 'stonewalling' of the compressor...where you physically can't move the compressed charge round the system as the engine can't get rid of it (use it)...probably because the exhaust manifold is the restriction (on the S3 it's my belief that this is the case).
With 'stonewalling' you can incrase the compressed pressure but get nothing positive out the other end...although with my S3 gaining torque with every increase in boost at peak torque, this would suggest that the K04 compressor was not 'stonewalling'.
With a decent inlet system, efficient filter etc and a decent IC system...I wouldn't expect to ever get surge...the ECU will hit limp mode well before you risk destroying a compressor with surge.
My experience with surge is that there are no second changes. Surge to wrecked. One directly follows the other!
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If you are holding 1.4 Bar at 6k RPM to get around 280HP you are pushing the turbo close to 165k RPM and if you read compressor maps the max for that turbo is 170k. Above 1.6Bar, efficiency of the turbo is not good,
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I don't believe this is even possible...
Even running the K04 flat out...I couldn't get much more than 1.2 ish bar at 6k RPM.
I just don't think the K04 can move enough air to generate the pressure at those sort of revs.
I know that the K04 on my old S3 was well out of it;s design range, or for that matter efficiency range...but you can run it, as long as you fully understand and address the problems associated with running outwith design parameters.
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and you will get stupid high intake temps which means the ECU has to ****** timing. Retarded timing means high combustion temps/EGTs and in order to compensate for that, it means dumping lots of fuel.
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True...the ECU winds back timing under high inlet charge situations...
But under 30 degrees at the engine, with 1.8+ bar peak boost isn't high temperatures...and logging the ignition timing values would suggest that thet were not being retarded.
EGTs are up...but again, you can roughly log them with VAG Com...and EGTs are far more likely to go high running lean, than they are running high boost - as long as the ICs are working!
The S3s EGTs are fine...as are the AFRs...infact, it's running slightly rich - even at silly high boost!
AFR of approx 0.85 under any boost condition you care to test it... so to some degree it is using fuel to cool the cylinders.
Also, my experience of retarding the ignition timing is that it reduces power, and decreases the temperature of the burn...reducing cylinder temperatures.
In my experience, winding on ignition advance will cause the engine to run hotter...never colder....which again needs a cooler inlet charge to exploit.
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You will get very high intake temperatures with more than 1.6 Bar and will only produce power when it's cold outside and I know David has some trick Intercoolers but they can only do so much.
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Again...I disagree.
I have never seen air temperatures above 30 degrees - summer or winter, road or dyno.
Hell, a standard S3 on standard boost has higher inlet temperatures...
Trick ICs can do exactly what they were disigned for...if they were designed and mounted correctly.
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Running over 1.6 Bar, or even not tailing off boost at high rpm (to 1 Bar at 7k) also means your backpressure makes the engine more prone to detonation which means even more retarding on top of what it's retarding from high intake temps and even higher EGTs
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Agreed...
This i've proved by running an Optimax high boost map on BP Ultimate fuel...you can detect the ECU pulling back the timing to protect the engine.
Logging the knock sensor's input to the ECU will also confirm this...
But, run the correct fuel, and it's not an issue.
Again, I dissagree with the fact that retarding the timing causes higher EGTs...I';ve found the exact opposite.
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It's all about diminishing returns - there is a point where if you go past it, you're just throwing money at your project.
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So very true...
You don't push the limits unless you are prepared to shrug you shoulders and say 'ah well...' when a turbo / bottom end lets go on the dyno!