Speaking of risks, I feel obliged to insert the personal version of a 'Safe Harbor' statement here. The tools, techniques, processes and opinions expressed herein are not intended to be formally instructional in nature, and I cannot accept any responsibility for issues or damages to yourself, your car, or your garage, created by performing the described actions. You're on your own, your mileage may vary, knock yourself out. Choose two.
Finally, pardon the length of this entry. It's a bit complicated and I tend to be, um, verbose.
The following describes the process I used to lower and level a 997S Cab after a set of Bilstein Damptronic coilovers and H&R sway bars were installed. Reviewing many Porsche forum entries and weighing them against the roads, driving hazards and habits that I'll be dealing with, I chose to lower the car 18mm from the stock ride height. The recommended range is 10mm - 20mm with the upper bound (where 'upper' is 'lower') being the preferred level. Bilstein recommends lowering a minimum of 10mm with the Damptronics. In general, with lower settings come improved handling, a rougher ride and the possibilities that your beloved sports car will become an urban farm plow - pushing it's front end through speed bumps, driveways and other metal wrinkling impediments.
The list of recommended tools are:
1. Floor jack (at least one)
2. Jack stands (at least two)
3. Torque wrench
4. Yard stick or equivalent - annotated in either millimeters or sixteenths of an inch
5. A micrometer - preferably digital (this is a personal preference but quite valuable)
6. The Billstein adjustment wrenches - co-packaged with the coilovers
7. Various breaker bars, metric sockets and wrenches and a soft headed hammer;
8. Laptop with a spreadsheet program - or a lab book and calculator. Or both :)
9. Dumbbell plates, equivalent to your driving weight. No fudging here.
10. Time. Unless you're expert, this takes a bit of time. But it's a bit like freshman chem class. A little bit of lab work and a lot of planning and documenting. You will not need to know how to interpolate a meniscus however.
Begin by measuring the baseline height of the car. There are numerous ways to do this, and they all assume that your car is currently set to the factory specs. Do this BEFORE the new coilovers are installed. Before performing these measurements, make sure the car is on level and smooth ground and try to have 1/2 tank of gas (minimizing variance as gas is consumed) in the tank. Do this twice. First without the dumbbell plates in the front seat, and then after. I used blankets to protect the upholstery before dropping the plates in.
Since this is a relatively exacting process, these measurements are important. After measuring, I would recommend that you construct a chart or spreadsheet, converting figures to millimeters, that lay out these initial measurements (pre- and post- weights), the chosen lowering amount, and the resultant height figure. You'll be using this to check your work when you're done. Create a column that is the amount of 'sag' that occurs when you add the weights. You'll be using this figure shortly.
I ended up measuring from the ground to the lip of the fender above the centerline of each wheel.
You'll be repeating this measurement a few times, so make sure you can do it accurately and repeatably. A couple of points here: I ended up using the measurements provided by a number of forum members to determine the proper stock ride height and using this as the baseline rather than measuring my own car. The figures I used are: front: 26.5 inches; rear: 27.5 inches. This is for a 997.1 S. The non-'S' has different tire specs so the height will be different. I originally tried measuring the gap from each of the four jack points to the ground. But they are less reliable because they are not perfectly flat.
Finally, I was sent this diagram, which is the Porsche factory method of measurement. It arrived too late to use, but you may want to try it.
After measuring, pour this data in to your spreadsheet or chart - converting figures to millimeters - to lay out the initial point, the chosen lowering amount, and the resultant height figure. You'll be using this to check your work when you're done.
Oh, did I mention that the adjustments can only be done with the wheels and tires off of the car? Thus you cannot determine if you've done all this correctly until you've reassembled the car and have had a chance to let it settle a bit. It adds to the excitement.
With all of this done, you need to get the wheels off. You can either do one corner at a time, one side at a time, one end at a time or all four at once. I chose the latter.
With the wheels removed, you'll be looking at an assembly like this (front):
The coilover assembly has two locking collars below the coil. These are the objects of your interest. The upper one is designed to pull the coil up and down against the strut and the other one is designed to compress against the upper and keep it all from moving - once set.
Before loosening the assembly, you need to take one more set of baseline measurements. These are to establish how much you must alter the length of the coilover (actually the coil bottom to strut base) after adjusting it. This is where I got lazy. As you can see, the coilover axis is not exactly perpendicular to the ground. Thus, shortening it one millimeter will not achieve exactly one millimeter of lowering. You COULD calculate the angle from perpendicular that it makes, compute the cosine of the implied angle and then determine how much you must alter the hypotenuse to achieve the correct adjustment of the vertical leg of the triangle. Because it was 'close enough' (I'm rather OCD and it pains me to admit that I guesstimated it) I assumed the coilover was perpendicular. It turns out that it's within the range of accuracy of my measurements and so it's a reasonable corner-cutting lab tip.
Be careful to measure each of the four corners. Don't assume that the two fronts nor the two rears match. They don't, but they will when you are done.
In the front, I measured the distance from the top of the hub assembly to the bottom of the upper locking collar.
In the rear, it's a bit trickier. I measured from the bottom-most thread of the assembly, to the bottom of the upper locking collar. It is actually quite repeatable as long as you are careful, just not as simple.
Once you have these measurements, on your spreadsheets or chart, subtract the desired lowering amount from these four figures. With one caveat. To achieve the proper ride height when you're IN the car, the drivers side must be lowered less than the passenger side. The difference is the amount of 'sag' (from the weights in the drivers seat) that you measured earlier. So, drivers side lowering = lowering amount - sag. Passenger side lowering = lowering amount.
Proceed by using the provided wrenches to unlock the two collars or bolts. It takes some firm pressure to do so. This is where I had to tap one of the wrenches with a soft-headed hammer. Then lower the bottom collar a bit to make enough room to measure the changes you'll be making. Then rotate the upper collar in the direction to pull the coilover shaft 'up'. Continue to measure, using the exact same locations and technique you used initially, until you achieve the corner-specific reduction specified in your spreadsheet.
Then relock the collars, making sure that the upper collar does not move in the process. I marked the collar to visually ensure that it did not spin. Completing the first corner, simply rinse and repeat.
Once you're done, remount the tires, and torque them to 94 ft/lbs.
That's it.
By this time, the sun is setting, the NFL playoff positions have been established and it's time to take your newly suspended car for a ride. Be careful when first driving to clear driveways and speed bumps. You'll need to get the feel of how much extra care you'll need in avoiding objects. Don't ask me how I know this...
Oh, the finished product:
