Right guys, I decided to do a simple experiment for you all. I have a runabout car in the form of a Ford Fiesta 1.4litre which is normally aspirated and has a forwards facing air intake which lies behind the front grille and below the lip of the hood. I made a simple scoop device out of a piece of black plastic guttering which I moulded into shape with a a hot air gun and fixed it close to the OEM air intake aperture. It took me about 45minutes to make it and fix it and cost me NOTHING. Here's a photo of it:
I've taken the car for a dyno run in third gear and logged it with my DashDyno and I've prepared a graph from the collected data showing the torque and HP plots of the same car, with and without the scoop fitted, as below:
As can be seen there is an increase in "real world" on the road performance with this simple scoop which is an increase of an average of 5.25% (calculated from all the data points) across the full engine rev range. The speed of the car under test was from around 18mph to 68mph in the same (3rd) gear.
I would therefore suggest that the RPI scoops will also show a gain although I don't know by how much.
I would still want to see the on the road figures for the RPI scoop though.