mklein9

There are two rubber air ducting parts that stick below everything else on the car's underside in front and get scraped and pulled out or broken all the time. These are the "wheelhouse air ducts". For reference, left side is part number 996.504.603.02. See the great diagrams at AutoAtlanta.com for the detail.

I ordered a matching left/right replacement pair and found that their installation consists of pressing a number of tabs into the plastic wheel housing liner (part 996.504.123.01) which has holes for these tabs very near its edge. Most of these were broken, so the duct flopped around after a short drive.

I've already spent $45 on the two ducts but do not relish the $300 to replace the liners.

Does anybody know what these ducts do? They appear to divert air coming from the wheelhouse toward the center of the car. They don't seem to pull air from the underbody into anything useful in the wheelhouse like brakes etc. If they can be simply left off, I'd be fine with that, but it seems doubtful their function can be so easily dismissed. Maybe they create some vacuum to pull air out of the wheelhouse?

Zanzibar Red 996

I also would like to know

knfeparty

I could guess but I have also demolished those things. Glad I'm not alone.

Macster

Generally they are there to improve/encourage air flow through the radiator ducts, reduce the amount of air that goes under the car, or (and) to improve front brake cooling.

Without a pic to precisely place them though I can't say for sure which of the above is the primary reason.

It is a good idea to keep them intact and operational and replace them when they are not.

I have to wonder a bit out how you are driving that these get broken all the time?

My 02 Boxster has a small air dam just ahead of each front wheel well and these last thousands upon thousands of mile. I might have replaced them each side maybe 2 times (3 tops) in over 270K miles of driving.

Even the front air dam on my 03 Turbo which is low enough to drag every day when pulling out of/into my driveway and into and out of my work driveway and in fact almost every driveway I encounter has only had to be replaced once in 110K miles.

mklein9

Here is a pic:


This is a pic taken from in front of the right wheel. I believe the air dam you are referring to is the flap sticking down directly in front of the wheel. The duct is on the right (in the pic). It doesn't seem to function as much of a dam, since its smallest dimension is pointing into the air stream. In fact, if the air dam and wheel are producing a localized high air pressure zone, this duct would seem to be trying to ensure most of it is diverted into the wheel house.

On that question I will have to plead innocence and blame the PO :-). I've had the car for under a year and 7k miles. The primary issue I've noticed is scraping on parking stops. When backing up again, these ducts get fairly easily ripped out. So, I have to leave lots of room when parking. The one and only downside of the X74 so far!

Macster

Looks like they are there to deflect air towards the outside of the car rather than let it flow down and under the car. Still hard to tell from the pics. Let me see if I have any pics of that part of a 996 laying around on my hard disk.

My Turbo's nose with that air dam is so low I can't even pull in over the parking stops/curbs. I have to stop short. I use the driver's side mirror and the curb line to know when (to estimate at any rate) when to stop and thus stop short of pulling the car too far in and damaging the air dam ($400 or thereabouts).

I suggest you develop a similar approach and learn to stop just short of the point at which the car's underneath is in danger of contacting the concrete.

Also, if you encounter a curb stone a bit higher than usual and off to one side this can possibly damage a radiator. I lost a radiator on my Boxster not from a stone being thrown up -- which everyone believes is the radiator killer (how it gets past the condenser I have no idea) -- when I hit some road debris (a tire carcass (Detroit Alligator)) just high enough to bust the lower connection of the driver's side radiator.

So I always pull into a parking space and stop short of possibly grounding the nose of the car on anything that can put undo shock or pressure on the relatively exposed radiators.

Ahsai

The air duct in your pic is the "exhaust port" of the hot air exiting the right radiator. Without that opening, the hot air after the rdiator has no where to go. The duct and the flap are to divert the hot stream away from the tire and brake. Excellent design

mklein9

Thanks Ahsai. That makes sense to me and is a good thing to keep in place. So... I've ordered one new liner to replace the one whose tab holes are pretty completely gone. Whether it's worth $150 or not is a lot less clear, but with my first track day coming up with this car it would probably be good to be safe rather than sorry.

KrazyK

I know mine are different than yours but when I bought both new front wheel well liners, they came with the piece your referring to. It was part of the assembled liner. View is from the front.

Loren

Here is what Porsche said in their 996 introduction Tech Book...

Shark Attack

Front brake cooling. Never broke one yet....

mklein9

Yes, I can confirm. I ordered the liner and it came with both rubber flaps. Really quick and simple replacement. I am giving parking stops a lot of clearance now.

mklein9

Thanks for the reference. The "diverter fins on the front axle bars" are probably the brake ducts that clip onto the diagonal braces (and are sometimes substituted with GT3 versions). I don't think that is exactly the function of these, but from the other prior responses and the info in this one it does seem like Porsche has carefully designed the whole wheel well area combined with the radiator exhaust path and this liner as one unit to bring in cool air and exhaust hot air in separate paths so they don't mix much. That is my rough take on this and may well be incomplete or just wrong.

Hurdigurdiman

I suppose if the car has been dropped, lowered or slammed down as these young modders like to call it, so it appears to be crawling along the road like a lizard, then these ducts plus other important Porsche parts will be compromised over rough ground or uneven surfaces. Porsche designers put them there for a good reason. If they were not needed then Porsche would not have added the slightest weight to their creation, so I would try to put them back on the car if possible. Question Porsche aerodynamics at your peril.

mklein9

Mine's an X74 suspension, so it's lowered 40mm in front. Liners and ducts are all there now. Track day coming up on 9/28, first one with this car. Now need a pad upgrade. :-)