Originally Posted by Gruppe-S
While the STI springs / valvetrain does accomodate for a higher lift camshaft than the WRX, the valvetrain is also designed for a lower revving engine / valvetrain. I would recommend using an aftermarket valvetrain such as the Helix valvetrain for the camshafts. If you are planning to keep your revs low and to stay with the stock valvetrain, please remember to check your valvelash clearances, etc.
Could I use valvesprings from another company? I'd rather not spend $450 on valvesprings if I could use Crower or DPR springs instead.