OE Style Variable Duration Chev 305-350 / Gen III (LS-Series) Hyd Roller Lifters Maximum low end torque without sacrifice of mid or top end power. More vacuum (up to 3 in.) and better fuel economy. Effectively lowers cam duration by approximately 10 degrees, up to 3000 rpm. F or use in OE hydraulic roller blocks. Note: These lifter produce a mild ticking sound (similar to mech. lifters). Made in the USA!