The KT4004 kit uses a S10100 valve spring is recommended for all applications where you are using a larger aftermarket cam, including road racing. Max recommended lift on this spring is .600" and max recommended RPM is 9500.
The S10149 Spring is for use with very high lift cams and in applications where high spring pressure is necessary. Also recommended for 1000hp+ turbo SFWD Applications.
Kits include spring bases, valve springs, titanium retainers, and valve locks