Today I saw several cars with a perforated metal grill in the bonnet scoop rather than the plastic half perforated one. Can anyone advise me of the source? Has anyone invented a rain deflector for this?

 

The gutter guards from home depot, its not cheap chicken wire stuff, its the thicker gauge, it comes in like 8"x48" or so-- its with the plastic guards, but this one is metal. Spray paint it black and you can use the existing screw holes from the plastic grill to secure the metal one.

Nothing to worry about with the rain... what type of filter do you have? OEM or aftermarket open filter?

If open, I ran a alta foam filter for over a year in big rainstorms up in new england with no issues. After the first rainstorm I checked it after driving for 45 minutes and it was dry. aftermarket filters heat up so much from the engine heat that any water on the surface of the filter evaporates quickly, either that or cools down the air going through it. It'll be safe. If you're really worried, you can get a waterproof bag from K&N to put over your intake filter. Everything else in your engine can get wet (at least to the point of whatever water will get through your hood scoop)