Tweak your boost levels with this GripTec "upper" LT4 pulley upgrade for your 1.7L LT4 supercharger.  The stock LT4 blower came on V3 CTS-Vs, 6th gen Camaro ZL1s and of course the C7 Z06.  This bolt-on upgrade allows you to change the spin-rate of the supercharger. A Griptec upper pulley upgrade is a cheap and effective way to boost power.
ZPE (the company behind the GripTec pulley system) has their own mounting "hub" (the ZPE hub) that's required to use this LT4 pulley.  If you already have the ZPE hub you can simply buy a pulley by itself.  Otherwise you can buy a pulley and hub combo or you can buy a hub separately.  The hub comes with a set of 10 titanium screws for weight savings and strength.