Bilstein Damp's - spring length change
 

as long as ride height is carefully maintained to avoid bottoming out, is there any other downside to running shorter-than-designed springs on bilsteins damptronics? i have a 06 C2S with damptronic's, aftermarket sways and drop links. they have been revalved/adjusted to accept heavier springs but the 500# i have do not have enough "sag". due to that, the lock rings are at the bottom of the threads already, thus i cannot lower the front end any more to even get to RoW specs. they are 8" springs. any foreseeable issues with running 7"? (again, as long as ride height is kept in check so as not to bottom out. i do not want to "slam" the car...only to take it RoW or maybe "race" height in order to make it perform better on track, etc)

All things being equal one would think a 1" shorter spring would lower the car 1". In your case you would still be on the bottom of the adjustment range. If you tried to corner weight the car you might end up needing to raise/lower one of the corners. If lower then you wouldn't have any room.

Springs have a free length and a compressed length. The distance between the two is what you have to work with prior to coil bind which will result in an infinite spring rate, not good.

hmm, wait, not sure i understand what you mean. i was saying that, with the current 8" 500# spring, i am at the bottom of the adjustment threads for lowering car. i.e. there no more threads in order to spin down the lock/bottom rings to lower the car, yet the car is still sitting too high. thus it seems to me, putting on a 7" 500# spring simply frees up an inch of threads whereby i would have greater freedom in setting the car to my desired height. i dont necessarily need an inch, i just need it a bit lower but in general, i want to have the extra room/threads in which to play with height anyway.

so back to my main question - i meant, other than being careful of ride height of course (making sure i wont bottom out or bind), are there any other concerns i should be aware of? like, does the shorter length change the linear rates somehow? or does 500# mean 500# regardless of length?

You are correct. I was referring to lowering the car 1 additional inch putting the car once again at the bottom of the adjustment range. Using a 7" 500 lb spring would allow you to lower the car 1 more inch. A 500# 7" spring requires the same amount of force to compress it one inch as an 8" 500 # spring. If you were to cut an inch from the 8" spring then it's rate would go up. But you aren't doing that so it doesn't matter.

If you don't mind, what rates are you using front and rear? I ran 500/650 F/R with Moton Club Sports on the street with a 993 and it wasn't too bad.

ah, gotcha. yeah, i'm not going to slam it by any means. i just need a few more mm's to take it to "race car" ride height.

the rears are stock damptronics and are about ~600. TPC is confident that 500 up front is not too much and that they can balance the car sufficiently with other tweaks to ride height/sway positions etc. besides, i LOVE the extra stability up front under braking - no dive whatsoever!