Any 101 Projects book worth a grain of salt needs to have a section on preparing your car for the track. The 911 Carrera has always been a popular weapon of choice as a dedicated track car. Its relatively lightweight construction, combined with its rear-engine placement, creates an excellent starting point for building the ultimate track car. I could probably write an entire book on the subject of creating the ultimate Carrera track car, but for now I'll just give a brief overview of some of the changes I would make if I were to turn a stock Carrera into a dedicated track car:
Install a permanent roll cage (Figure 1)
Upgrade braking system (Pelican Technical Article: Big Brake Upgrade for the Porsche 911 Carrera)
Upgrade shocks to an adjustable system (Pelican Technical Article: Performance Suspension Lowering your Porsche 911 Carrera)
Install the GT3 adjustable control arms (Figure 9 of Pelican Technical Article: Alignment in your Porsche 911 Carrera)
Have a full racetrack alignment and corner balance performed on the car
Install adjustable sway bars (Pelican Technical Article: Performance Suspension Lowering your Porsche 911 Carrera)
Replace the doors and hood panels with fiberglass units
Use lightweight race wheels with slicks
Install a fully certified fuel cell
Install a fire suppression system
Upgrade the transmission to include a limited slip (Pelican Technical Article: Replacing Porsche 911 Carrera Limited Slip Differential Carrier Bearings and Seals)
Install a real-time data logger and/or electronic dash computer
Install racing seats and a five or six-point harness
Install an Accusump and/or the deep-sump kit
Install an aftermarket MOMO wheel
Remove as much weight as possible (see next section)
A project on track preparation would not be complete without discussing the option of placing your car on a diet. The benefits from weight reductions to rotational components in the engine are twofold--they not only reduce the rotational mass that the engine needs to spin up, but they also reduce the total weight of the car. These rotational components exist all over the car--not just in the engine. All of the rotational drivetrain components (wheels, transmission gears, axles, brake discs, etc.) have a significant effect on your car's overall performance. Using lighter-weight wheels, for example, will have a similar effect to reducing the weight of your flywheel--the drivetrain will accelerate faster, and the total mass of the car will be reduced as well. Again, the gain is twofold. It is for this reason that most racers try to remove as much mass as possible from drivetrain components when lightening their chassis.
While reducing the mass of drivetrain components can produce the most efficient gains, you can go only so far. This is because the drivetrain is responsible for delivering power to the wheels and accelerating the car. You can remove only so much weight--you don't want to weaken the drivetrain to the point where it is going to fail. The second-best thing to do is to remove weight from the chassis of the car. Theoretically, a 10 percent reduction in weight is equivalent to a 10 percent increase in equivalent horsepower. On a 200-horsepower, 3,000-pound car, it may be far more practical to remove 300 pounds than it would be to produce 20 more horsepower from your engine.
So what can you do to reduce weight? There are a couple of rules of thumb. The first place you should remove weight is from "unsprung" components. These are the parts of the car that are not supported by the suspension. Examples include trailing arms, A-arms, brake discs, wheels, etc. The next-best place to remove weight is from the highest points on the car (sunroofs, windscreens, etc.). Removing weight here helps lower the car's center of gravity. Next, you want to target the mid/rear of the car. This is because the Carrera is already very tail-heavy due to the rearward mounting bias of the engine and transmission.
If your goal is pure performance, you can lighten your car significantly simply by removing or replacing the following on the car:
Remove the entire heating and air conditioning system
Remove window regulators/support braces in doors
Replace glass with Lexan
Replace deck lids and doors with fiberglass
Remove most interior components (carpet, door panels, interior trim)
Remove undercoating on the chassis
Replace the drivers/passenger seat with a lightweight one
Move or replace the battery with a lighter one (Porsche has a brand new Lithium-ion battery that just came out for the GT3)
Remove any unnecessary components from the front trunk (spare, jack, etc.)
Remove the DOT bumpers and replace them with fiberglass
Remove stereo system, amplifier, and speakers
Remove the convertible top and replace it with a fiberglass hardtop
Install Cross Drilled brake rotors
Remove power mirrors
Most of this weight removal can also be done to a street car, but any weight removal must be balanced with the practicalities of daily driving. While the motto "if it doesn't make the car go or stop, it's just extra weight", there are exceptions. If you enjoy air conditioning and a good stereo, then you probably won't want to sacrifice these amenities for the improved performance. However, if your mission is to maximize performance, you might be surprised at how much of a difference weight removal can make.
Any dedicated track car requires a welded-in roll cage. Be sure to have someone install it who has previously fabricated one for a 996 or 997 Carrera. Shown here is a roll cage installed in a Boxster so you can see the cross bracing, door protection and shoulder bar for the 5 or 6 point system (you don't see a lot of Carrera Cabriolets as purely dedicated track cars). If you are planning on tracking your car make sure you check with the sanctioning body of where you are going to be competing, as different organizations have different rules.
Shown here is a Kinesis K28 wheel, one of the best choices available in high-performance wheels. This wheel has a reputation for being one of the lightest and strongest that you can buy for your track car. The wheel centers are forged from 6061-T6 aluminum and are mated to rim sections that are spun by computer controlled machines assuring trueness and consistency throughout the wheel. These wheels not only look cool, but their performance and reliability has been proven time and again at various races like the 24 Hours of Daytona.
Here's a shot of two Porsche interiors that have been gutted and prepped for the track. The car on the left has had a replacement dash computer installed in front of the normal gauge display. This programmable dashboard allows you to monitor all of the systems of the car, while also logging data such as lap times and engine performance. It also has a quick release steering wheel. This is very common upgrade in track cars, as it helps getting in and out of a vehicle that has a full roll cage. On the car on the right, you can see that a custom box has been fabricated to raise the gearshift lever off of the floor. This allows for less movement from the driver's hand to the lever, resulting in quicker shifts and more time with your hands on the wheel. In addition, both these cars have had most of the interior gutted and removed, as well as lightweight seats, full cages, and five-point racing harnesses.
Here's a photo of an Accusump installed in LN Engineering's Boxster test car (it is easier to see the system mounted in a Boxster than a Carrera). The Accusump is a cylinder-shaped aluminum storage container that acts as a reservoir of pressurized oil to be released when there is a drop in the oil pressure. The Accusump is connected to the pressure side of a Carreras oiling system (typically through an adapter on the oil filter, inset photo) and is charged by the engines own oil pump. Its simple, efficient design revolves around a hydraulic piston separating an air pre-charge side and an oil reservoir side. The oil side of the Accusump has an outlet that goes into the engine's oiling system, controlled by a valve. On the air side it's equipped with a pressure gauge and a schrader air valve, which allows you to add a pre-charge of air pressure to the Accusump. Installing one of these on a dedicated track 911 helps compensate for the fact that the 911 engine does not have a dry-sump oiling system.
Nothing says fun quite like driving your Carrera on the track. The car shown here is being driven at California Speedway, but there are usually tracks within easy driving distance of most major cities. While the Carrera is a wonderful car to drive on the street there is nothing like testing the limits of you and your car in a safe environment like a race track. Be careful though, it can be a very slippery and expensive slope.
Big rear wings are a staple of track cars, and no matter how many events you go to, you'll always be able to find a wing that you haven't seen before. I took a whole bunch of fluid and aerodynamics classes when I was at MIT, but even armed with that knowledge, I think it would be difficult to find the optimum wing design and settings without the use of a wind tunnel. It's tough to tell whether the use of a rear wing adds enough benefit to counter the added weight and wind resistance, that being said, one of the added benefits of owning a Carrera as a track car is the involvement of Porsche in racing. You will be able to easily find a wide variety of Porsche and aftermarket wings that will work with your Carrera.