Quote:
Originally Posted by old greg
That is incorrect. It is usually the case, but a well designed system will produce higher compressor outlet pressure than turbine inlet pressure over a certain operating range. The thing to keep in mind is that the work balance between the turbine and compressor isn't about pressure change, it's about enthalpy change.
Just ditch the wastegate, problem solved.
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Sorry I didn't specify what I meant by pressure at the exhaust. I was talking about the "otto cycle" part of the engine, the operation of the pistons independent from the turbine and compressor. Aka the engine is always wasting some pressure when running at full volumetric efficiency, lower compression ratio/retarded timing means even more wasted pressure, boost wastes even more.
Also I think the nature of turbos (not needing all the energy in the exhaust to compress the air since there is significantly more pressure at the end of the expansion stroke than there is at the beginning of compression stroke) means the turbine is typically "undersized" for producing useful additional power, so the lower A/R, larger turbine wheel would do a bit better (especially since lower A/R would make it act more like an impulse turbine).