The guy I bought the radix from had 3 pulleys in the box. The 3.75" that is on the Radix now and two aluminum ones a 2.75" and a 3.25", at least that is what he said. There are no markings on the aluminum pulleys and I don't know how to measure them to be sure. I get nervous about running more boost than what is provided with the unit, mostly because I don't know what a stock 5.3 can take. The 2.75" would probably blow my motor and the 3.75" that is on the Radix now is bigger than the 3.4" that is recommended for my truck so why would I wanna use that? The 3.25" would make about 10 pounds maybe? Not sure what else I need to beef up before I go to 10 #'s. Hopefully in 24 hours I will find out what a 3.4" feels like!!