Since I had to disconnect the airbox to replace my upper radiator hose, I figured it was a good time to install the ECU spacer that I pulled off my old V50. If you don't know what these are about, it is a spacer that Ford used on the European Focus RS that had the Volvo 5-banger turbo engine. It goes between the airbox and ECU to move the ECU out to reduce how much the cooling fins impinge on air flow. Cooling of the ECU is still good as they are still in the flow with the present spacer thickness. There is a guy on C30Crew Market Place (http://www.c30crew.com/forum/showthr...ghlight=spacer) that fabricates these or there are some on ebay. Some thicker ones are available but I am not sure about ECU cooling. Obviously if you are running a CAI this is not necessary.
The only down sides is that it can make the airbox more difficult to remove for repairs and you have to modify the plastic ECU cover for it to fit.
As with my previous car, the benefit is in the throttle response. The benefit seems greater with this car with the manual tranny though. This will not increase boost as that is governed by the computer. It only allows better flow to achieve boost more rapidly.
Airbox with ECU removed:
Spacer sitting on ECU showing cooling fins:
ECU reinstalled with spacer: