I would recommend the Group A set from Ford Motorsport.
This is the only thing I know that worked. It is not cheap however.
It consists of a 10 liter tank, 2 supply pumps and a large high pressure pump.
You do need the nozzle from this set and a couple of valves. Anything else I found not to work properly and can damage the engine.

A cheaper version is water spray. You spray water to the front of the intercooler. This way you don't need the high pressure pump and the special nozzle. Any small pump (like a pump from the windscreen washers) will do.