http://www.pbase.com/klin/image/135685208

I had an extra cover so just to experiment I cut it up. With it, ODB2 on my 2000NB showed a 4C coolant temp reduction at the end of the back straight at Shannonville Motorsport Park. (Back to back runs with it taped over and open).

 

Interesting!

 

Stupid question. How'd you get the cuts even. Been looking into this kind of thing and terrified to go dremel crazy on my only bumper.

 

I'm just gonna go out on a limb here and guess he used a stencil

 

Yes a stencil was used. I based the pattern on the hood extractors from late 80s Group B Opel Manta Rally cars.

The cuts were done using a 1" wood (spade) bit joined with a Dremel fitted with a reinforced cut off disc. Then sanded smooth with a Dremel 1/2" drum sander. I cut up a cheap mouth grill and glassed it in place behind the holes.

The plastic cuts very easily, just take your time. I figured using smaller holes instead of one big one would preserve some of the structural integrity - it seems pretty strong and stood up well to my last lapping day at Mosport on the big track where it saw 110+mph on the back straight.