Permission to publish this article is provided generously by Robin Sun at www.p-car.com. Be sure to visit his site for loads of 993 info!
First, jack the front of the car up, and remove the bumperettes. You do this by first prying open and remove the rectangular rubber cover and then unbolting the two 8 mm nuts. After removing them, unscrew the philips screw that holds the factory fog/parking light and pull it out so that you can disconnect the wires. Unclip two electrical sockets and remove the light.
Remove both side wheels and fender liner as shown on bumper removal DIY
Remove three screws that hold aluminum oil cooler cover. Before you do this, mark the bracket so that you don't make the hole for the duct too low.
Take the duct and use it as a guide for marking the hole on the oil cooler you removed earlier. You want to make the hole as low as you can. (See the arrow pointing the thin line where the bracket position is marked). You can either use 2.5' hole drill or "tin snips", I found using the snips to be the best, 2.51/2 drill is little too small and by using snips, you have more freedom to adjust.
Make the hole also as close as possible to the chassis of the car. You need to cut the hole so that it's open to the inside of the plate, otherwise you have to pull the duct through it, rather than just installing the plate afterward, doing this way, you'll get really good and tight fit.
You want the opening to be as tight as possible, otherwise you'll lose some air that's supposed to go through oil cooler.
You also need to cut the rubber gasket, make sure it will be a tight fit.
Now you're ready to pull the hose through the fender to the wheel well area.
Pull the hose to the wheel hub but leave enough extra slack so it allows you to turn the steering wheel from lock to lock. End of the duct will go into an opening next to the brake caliber (you'll see it when you're there). This way the duct will blow air right into the brake disk, which is what you want it to do.
You also need to "squish" the end a little so that it will fit in there.
Install the oil cooler plate and "flatten" a section of the tube in the between the hub and the oil cooler. This will allow enough clearance so that your wheel doesn't rub. (You can see the flat part on the photo).
Now you need to make similar holes to the fender liner (you need to cut two holes since there are two separate plastic pieces on the fender liner). Put the fender liner in, as you'd be installing it and mark the position where you're going to make the holes (again, as close as possible to the chassis and as low as possible).
Install the fender liner (but leave two lower screws loose at this time) and three zip ties (see the arrows showing the location on the photo). Front zip tie will go under the fender liner, once it's in place, you can tighten the screws. Now tighten the zip ties and make sure end of the duct is still in its place. (In case you're wondering, that photo is from previous installation when I did this on my car)
Next, connect the two wires from the fog light to the wires from the car.
You want to connect the two wires from the round socket, which for the fog light. After that, mark and drill a hole to the new fog light/brake cooler so that you can secure it into its place, (it will be screwed to the same bolt where original fog light was attached.
Photo shows how it looks finished (although on the photo, it's still unpainted).
Now, have a beer (or something else to drink) and prepare for the PITA part!
Same procedure as on the other side until it's time to make a hole to that aluminium plate.
Well, except on this side it's not removable, and it's thicker.
You could remove the A/C assembly so that you'd have good access and you could make a nice hole to through that plate but I chose not to do so. Not very 'Porsche engineering' but works.
Loosen up the A/C radiator from its bracket so that you have little better access for making the opening and also pulling the duct.
Make two cuts with the metal hand saw and then bend a portion of the plate for the opening of the duct. Positioning will be same as on other side.
Last image shows the piece bent backwards and duct already pulled through.
Also here is a gasket, which you need to cut, and again, make sure it's a tight fit.
Once you've done the opening, you can start pulling the duct through the fender. There is one little vertical piece (right behind where the fog light was) that makes reaching it very difficult, this is the part where you need two person one which pulls the duct and while the other push it.
Be careful so that you don't rip the duct because it's tight.
Other option would be to cut the horizontal piece behind the fog light out, I chose not to do that because fear of rust problems.
Then just do the same things you did on the other side and you're done!
Your brakes will now have more airflow and that means they run cooler.
NOTE: Parts are no longer available for the fog light/air duct as of 11/1/2016.