Injecting prior to turbo comp' impellers

[hotrod]

I think the answer to your question can only be answered in context of a specific engine turbo setup, and your specific performance goals.

If the turbo is of adequate size, so it can feed the engine without straining at max rpm, and your going for max power, then post intercooler would likely be the best in my opinion.

If the turbo is a bit undersized and your pushing its air delivery capability, then I think either pre-compressor or a bit of both would be best.

There is also the consideration about ease of implementation. If its nearly impossible to squeeze a spray nozzle inbetween the intercooler and the throttle body (which is almost the case for the WRX) then the simplicity of pre-compressor injection has to be considered as well.

There may also be an advantage to over injection pre-compressor or pre-intercooler and then cooling to super saturation. It would be hard to beat a true fog of microscopic water dropplets for detonation protection I suspect. Only testing will tell for sure.

It's obvious that the WWII military aircraft did quite well with pre-compressor injection, so it may be that the only thing that really counts is the suspended water fraction and it may not matter much how it gets there once its in the cylinder.

I guess the question is, which of several problems is the most urgent for you to resolve on YOUR setup. Detonation (not an issue for a diesel), might depend on the degree of evaporation vs suspended dropplets in the combustion chamber, high EGT's (probably only dependent on the total water fraction, max power ( depends on highest VE so pre-intake valve cooling would dominate).

I think we sometimes forget that WI can be used to resolve several different problems and the setup that most effectively solves one, may be less effective for another.

Larry