996 Ducktail Grilles

Many find the appearance of Porsche's first water cooled 911 a bit bland. One way of addressing this is by fitting an aftermarket ducktail instead of the retracting wing.

This also sheds some weight from behind the rear axle - a win-win situation especially in a car with a rear-weight bias. Unfortunately the grille supplied with this part is typically nothing more than a flat mesh which may be sufficient for a track car but lacks the aesthetic refinement one would expect for an upmarket road car. How do we solve this?

Steps

The first step is to 3d scan the rear lid and import it into CAD. This will provide the basis upon which a new design can be modeled. We only need the outside shape so in this case it was done with the lid fitted to the car.

3d Scanning

One of the interesting aspects of 3d scanning is how it highlights imperfections which can't be seen with the naked eye. In the harsh artificial light of cyberspace every small imperfection, dent and undulation is exaggerated, as can be seen below.

In real life this part was sanded down professionally, painted and polished to a high gloss, and none of this is visible on the car. This makes 3d scanning a valuable tool for car restorers and a nightmare for body shops.

Design a Grille

The second step is to design a grille which will fit within the confines of the scanned area while keeping in mind that this part will have to be 3d printed.

This opens up design possibilities which would have been impractical with injection molding or casting. However 3d printing comes with its own limitations which have to be navigated around throughout the design phase.

Curved ribs

The car has virtually no flat surfaces so we decided to use curved ribs as the principle design element with thin, angled vanes running between them. The vanes were angled to be as non-restrictive as possible to the air path into the engine bay.

This means that the engine and air inlet are essentially open when viewed from the front but closed when viewed from the rear, which is good to keep falling leaves out.

We were initially concerned about engine temperatures especially over 50mph at which speed the rear spoiler automatically pops up to increase downforce and to let in more fresh air.

We couldn't detect any adverse effect on temperatures even in extreme ambient heat. If anything the car ran a bit cooler on a hot day than with the stock lid.

If cool air flows so easily into the engine bay then it stands to reason that hot air should escape equally well. So we removed the hot air extractor fan which blocks the right-hand side grille. We closely monitored engine soak temperatures (after hot runs on the road and dyno) and didn't see any difference. Presumably the hot air escapes so fast through the non-restrictive grille that an extractor fan is no longer needed. We tested it in ambient temperatures of over 40C without any issues.

The material we chose for the grille was carbon-fibre infused nylon-12 which can withstand prolonged temperatures of up to 160C.

This is more than any engine grille should ever see unless the engine is on fire.

In terms of durability it exceeds regular plastics such as ABS and has the added benefit of being UV resistant and lightweight. Since this is not a stressed part the choice of material is a slight overkill but these parts sometimes find their way onto rally and off-road cars which see a fair level of abuse. So, as always, we cater for the worst case scenario

The end result looks aesthetically pleasing and fits in with the rest of the car. These grilles have survived many adventures in harsh conditions as can be seen in the photo collage. The 996 test mule (which is now living a quieter life in the UK) spent years as test bed for various technologies in South Africa, often in blistering heat and on unforgiving roads.