Dougal I make mention of high emp as I read mmp customers were cranking up preload in an effort to build boost .
The turbo is often blamed for lack of boost but it's not always the problem . It can only do as it's told .
I suspect fueling as I've had better than reported results with larger/ less suited turbos . I could be wrong though, It could be something intenally causing resistance . Also the .42 a/r turbine housing will see higher emp at high power levels .
You need to pump numbers to this "higher emp" statement. Otherwise it's meaningless.
For my numbers, a turbo that delivers EMP lower than boost (at 1800rpm) with a hot turbine can deliver EMP of double boost while accelerating to higher rpm with a cold turbine (40psi EMP, 20psi boost).
The 40psi EMP is not a problem that needs solved. It is the only way turbine can extract power from cold exhaust gas. Anything you do to reduce that 40psi (i.e. weaker wastegate spring) will reduce the performance of that turbo in that condition. Reducing boost and richening AFR.
Turbines are driven by temperature, pressure and flow. Reduce any of those and you reduce their power.
You said you hadn't measured shaft speed, only assumed it based on boost . You also said emp kills power . But then disagree with what I say
Hang on a minute. I did not say "assumed", I said "approximated". Approximation in this case is by calculation. But there's no point doing that unless you are worried about over-speed.
Excessive EMP does kill power. But EMP is also what drives your turbo. Try to kill EMP and you've killed all boost.
Doing things to drop EMP (like using weaker wastegates) have consequences for turbine power and boost. The only single thing you can do to improve EMP while not hurting turbo performance is to find a more efficient turbine for those operating points.
Wastegates do not change a turbine map or characteristics. All they do is bypass exhuast to control boost.
That's it.
I have a good example here of a particularly badly suited turbine that I built to a turbo and fitted anyway. At 3000rpm with 15psi boost it was taking 60psi EMP. The engine produced no power and that was all the boost it could produce.
Same turbo compressor with a better suited turbine and it was around 25psi EMP for 20psi boost.
I've fitted a larger turbine housing to the same (better) turbine wheel and compressor for another test but unfortunately mislaid my EMP gauge at the time so I have no EMP numbers but they were lower.
Top end power was great, low end sucked. Turbine could not choke the exhaust enough to generate enough EMP to produce enough shaft power.
The bigger turbine housing also bought lower fuel economy. Mainly because I had to go down a gear more often.
Shaft speed can change independent to boost when emp is excessive .
No it can't. Follow shaft speed lines on a compressor map. To change compressor speed you're moving between these lines which changes PR (boost).
