It's tough for find non-GT springs with the torsion beam setup. However some people have had mild success with Eibach springs made for the Hyundai Elantra (AD) [Part Number E10-42-039-01-22). But as noturbonoproblem suggested, if you're picky about your appearance and ride heights, better go with coilovers.
For warranty it will only void suspension warranty and possibly make it difficult on any other components (ie- premature wear of the shocks, suspension components, bushings, etc). The thing to keep in mind is the insurance policy. Some insurance companies are very strict about aftermarket modifications. If you don't get their approval beforehand in writing, and you were involved in an accident and they found out you had aftermarket springs on your car, they can potentially void your policy. It rarely happens but they can void it depending on any small print in the policy.
For warranty it will only void suspension warranty and possibly make it difficult on any other components (ie- premature wear of the shocks, suspension components, bushings, etc). The thing to keep in mind is the insurance policy. Some insurance companies are very strict about aftermarket modifications. If you don't get their approval beforehand in writing, and you were involved in an accident and they found out you had aftermarket springs on your car, they can potentially void your policy. It rarely happens but they can void it depending on any small print in the policy.
