Pics & Review of My Bilstein PSS10 Lowered Red Turbo by cannga

8 minute(s) of a 612 minute read

11-26-2009

1. Coilover versus Lowering Springs: The "suspension's heart" consists of 2 parts: a damper (aka shock absorber) and a spring. You could elect to change both at the same time, which is called "coilover" (spring over the shock absorber) or you could change just the spring, aka "lowering springs." It's called "lowering" because all of these Porsche 911 springs also lower the car 1 inch/24mm.

Coilover is considered the gold standard for a few reasons:

*it's a ideal solution where spring and shock absorber are designed to work with each other (as opposed to lowering springs, where the new springs are used with the old stock damper), 

*the height is adjustable,

*possible to corner balance when used with adjustable drop links like Tarett's.

*the shock absorber is of much better quality and design than the stock shock absorber. 

Lowering springs offer a simpler and less expensive alternative to coilover, and good ones such as GMG and Techart do actually work well and get very good reviews. There are various reasons that I chose coilover over lowering springs but for some one of the biggest problem with lowering spring is that you cannot adjust the ride height. All lowering springs on market that I know of lowers the car by 1 inch (24mm). For comparison my car is lowered 12mm and I think it's a little too much already for a daily driver because of the front lip scraping.

Second, lowering springs are better than stock because of the stiffer spring rates, but you are forcing the stock damper to be operating out of specs: a. piston position is out of spec as it is much lower, and b. damper is not designed for stiffer spring (if stiffer spring is used). The risk is of seal/damper failure and you'll end up spending money a second time for a new and proper coilover system like Bilstein Damptronic. If you call the manufacturer of the stock shock absorber, which happens to be Bilstein also, they will tell you the same thing.

No rates are available for the 3 most common lowering springs, GMG, TechArt, H&R. The (unconfirmed) rumor is that GMG is stiffer than TechArt, which is stiffer than H&R, and H&R might be softer than stock! It should be noted that the lowering springs are progressive, meaning there are 2 rates, initial (softer) and final (stiffer), and we don't know which of these rates the above rumor refers to.

Historically, if you look at old posts and users reports, you will see several cases of people using lowering springs at first, then eventually switch to coilover; and *never* the other way around. So although I think lowering springs are better than stock, I do think that it is a much better idea to go straight to coilover from the beginning; you actually might save more money in the long run. A few users have also reported what sounds like wallowing, or a sense of loss of control or instability with lowering springs in high speed cornering. Whether this is true or merely anecdotal, it is consistent with the behavior of an under-dampened system, such as when you put stiffer springs on the stock shock absorber.

Bottom line: Lowering springs do work, is cheaper, and is simpler to install, but if you ask a competent tuner, you will be told that if you could spend the extra cash, a complete coilover replacement is overall a better solution and leaves no nagging questions, especially for the hard-core enthusiasts. 

2. 997.1 versus 997.2 Suspension: Going through the recent review in my favorite US car mag, Excellence Magazine, I couldn't help but notice that comments from Porsche engineers, and the changes to the 997.2 Turbo’s suspension, very much parallel the ideal of the suspension mods that a number of us have done to the first generation Turbo. 

In summary, the changes are as followed:

• Stiffer rear spring

• Stiffer anti sway bar: Front bar only for cars without PTV, front AND rear for cars with PTV. (I think I have an explanation for this. Ask if you want to know.)

• Stiffer rear bushing to "control lateral movement." Although I don't know which bushing they are talking about here. Reading this one almost brings tears to my eyes. I mean, this is deep into after-market US-style modding! This has got to involve the rear toe control arm here, I think.

• PTV. Reduces understeer. I assume improve the rear end "rotation" into corners.

• PTM: More gradual change and more rear bias; in essence the car behaves more like a RWD cars in corners. Yes the word “drift” was mentioned! (I have some misgiving about this particular change, reducing front traction in a daily driver with 500 hp. Faster at the track yes, but is it safer?)

Since my wife is preparing Thanksgiving meal soon, this post can’t be too detailed.  I’ll have more quotes to add, but for now, I am glad that Porsche appears to be receptive to scathing reports on how soft 997.1 stock suspension was and how the stock alignment has too much understeer.

Judging from the numbers, the 997.2 Turbo appears to be right in between stock 997.1 and Bilstein as far as spring stiffness is concerned. Surprisingly, the rear spring is now progressive (Not sure I like this; but there are numerous other changes and I am not about to question Porsche engineers’ decision!). The car’s mission as primarily a daily driver with occasional track time is maintained.

If I have to take a guess based on reading alone, this would be my prediction: With respect to handling, the 997.2 Turbo has more oversteer (from PTV and PTM) and will feel a touch stiffer/tighter than stock 997.1 Turbo. It is however not quite at Bilstein Damptronic level and this mod is as critical for second generation as for first.

There is one major advantage to 997.2 suspension that should be mentioned: its generation 2 PASM system. 997.1 generation 1 PASM has a design flaw: Normal setting is way too soft, and Sport Setting is way too stiff, jittery, and un-useable for street driving. Porsche actually acknowledges this at the time of 997.2 release and true enough, 997.2 PASM is night and day better, particularly the Sport setting: it is much less jittery.

Happy Thanksgiving.

3. Spring Rates Summary: Spring rates are the heart and soul of the suspension system, they tell you the intention of the car/vendor: Is this going to be a street car or is this gonna be a track star :-). Note that the damper also contributes significantly to how the car feel: a Bilstein with 400/600 springs will feel completely different from a JRZ with 400/600 springs. This is because the damping forces in the 2 coilovers are different, JRZ has damping forces designed for heavier springs and for more vigorous requirements of track use. Also other factors such as constructions are different; one example: Bilstein re-uses the stock's top mount/bearing which has rubber parts to soften the blow, JRZ to best of my knowledge does not - anyone pls correct me as needed. So although the spring rates give you some important idea, the bottom line is you won't know until you actually drive the car.

Source for spring rates below: Very extensive web research (ie no guarantee whatsoever of accuracy :-)) and Excellence Magazine. GT3 rates are posted for comparison, and do keep in mind the GT3 is around 300 lbs lighter than Turbo, meaning if anything the Turbo's springs could/should be even stiffer than GT3's. Also, 997.2 Turbo's engine is lighter, making the increased spring rate noteworthy. Anyone with more info please correct as needed. 

Stock 997.1 Turbo: 

Front: 206

Rear: 457 Linear 

Stock 997.2 Turbo

Front: 206

Rear: 514 Progressive (342 initial, 514 final) 

Bilstein Damptronic For 997 Turbo

Front: 340 Linear 

Rear: 565 Linear 

Helper springs (no contribution towards rate) 115 front, 145 rear

Bilstein Damptronic in my Turbo  (stiffer springs than Bilstein OEM)

Front: 448

Rear: 600

Ohlins Road & Track For Turbo

Front: 400

Rear: 685

KW V3 For Turbo

Front: Progressive, unknown final rate, possibly around 300

Rear: 970 

For 997 GT3: 285 front/ 970 rear

For 997 C2S: 230 front /740 rear

Moton/JRZ For Turbo (starting min. rates, stiffer if needed)

Front: 500-600

Rear: 700-800

Stock 996 GT3:

Front: 225 Linear

Rear: 550 Progressive

Stock 997 GT3:

Front: 257

Rear: 600

Here are some technical data of Bilstein Damptronic coilover for anyone interested:

Front: Helper 80 lb/in spring rate, 60mm length; main 340 lb/in rate, 151.5 mm length; ID 70mm for both helper and main springs.

Rear: Helper 80 lb/in rate, 60mm length; main 565 lb/in rate, 200 mm length; ID 70mm for both helper & main.