I followed Clive's advice last year and fitted the grilles to my 997.2 turbo. Very happy with the result and there's no impact on operating temperature. Porsche will tell you that the grilles will restrict air-flow which may be the case but it is nothing compared to the restriction caused by the accumulated debris. As it happens, a pheasant came to grief when it hit my car which damaged the plastic frame of one of the side vents so I am waiting for some good weather to take the front off again and replace the frame, hopefully reuse the mesh in that section and see how well they have been protecting the aircon rads. Before the grilles, it was the most unbelievable mess in there. Taking the front off may seem daunting at first and it's always a job to do with care so as not to damage either the car or the front but once you've done it once, it's really quite straightforward. Everyone has their own tips, mine would be to remove both headlights and jack the car up on both sides to allow you to get to the wheel arch liner fixings without removing the wheels. I fitted the grilles to the front with a combination of self-tapping screws, the type with a wide flat head and small black cable ties which if you have slats can be hidden from view.
