Injecting prior to turbo comp' impellers

[cheekychimp]

Theory:-

i) By using a turbo exhaust housing with a smaller AR we can help a large turbo spool faster, but the trade off is that the housing is unlikely to be able to flow enough air in the upper rpms to be able to realize the full potential of the compressor.

ii) By using pre-turbo water injection to move compression away from adiabatic towards isothermic we improve compressor efficiency enabling it to flow more air.

Question:-

If we reach a point whereby the exhaust housing is already creating a restriction to airflow, will pre-turbo injection

a) Have NO noticeable effect because the housing is unable to support any further increase in flow?; OR

b) Make the air denser thereby allowing more air to pass through the housing?