Skunk2 designs, develops and tests all of our valvetrain components in-house to ensure the highest quality and greatest performance gains. During development, all valvetrain components are tested in engines both on the dyno and on the road. Manufactured from the best materials available, our valvetrain components provide exceptional performance, reliability, and quality. Skunk2 valvetrain components are standard issue on all the project cars and race cars we build and support, and are available in our premium Pro-Series line and our Tuner Series line, both offering exceptional performance, reliability, and quality. (Skunk 2 Raing Valve Springs are sold in sets of 16)