Custom dual valve spring coils by Bisimoto. High RPM duty windings with excellent longevity, as the factory single spring intake, and dual exhaust are far from optimal for performance applications. Excellent for turbo, high rpm street n/a and race duty. Comes with 12 dual coils, and should be used with stock spring bases and retainers. Spintron tested to 14,020 rpms! A must for the avid A-series enthusiast.