SHELBY GT 350 Member
Joined: Sep 2010
They're supposed to be different diameters than the stock pulleys, that's the entire point. I've had those same ones on my car for 6 years, no issues despite all the bad stuff that's been said about piggyback pulleys. Cools fine, charges fine, runs fine. Don't really do a whole lot besides dress up the engine though, and if you ever go s/c you'll need to put the stock pulleys back on because as the term "underdrive" implies, the motor won't spin the blower as fast as it could with the stock pulleys.
2001 GT Convertible
All the usual bolt-ons 1967 Coupe
200 I6, C4