This is the 5/16 Stealth Plenum Spacer Upgrade for the 03-06 350Z, 03-06 G35 Sedan, and 03-07 G35 Coupe VQ35DE Engines. Gains from 12-14HP, simple and easy install. Works with OEM Strut Bar and Engine Cover. Iso Thermal Spacer Reduces Heak Soak and helps prevent power loss. Iso Thermal Gasket also allows upper and lower plenum to run cooler.