Looking at wheels on Imagewheels and they have a 3pc cast and a 3pc billet wheel section whats the difference between the two

 

Isn't cast when the wheel is molded in a reverse wax model casting of wheel then filled with metal then cooled to make wheel.

Billet begins with a block of aluminum and is milled along with some liquid or CNC process.

Usually, not light unless they go through other more expensive processes. Billet wheels look nice look to them though. Check out you tube videos for the manufacturing processes, not much on billet or cast but alot more interesting techniques that BBS and Rays Engineering employs.