The F150 pulley is the crank pulley off a F150. It measures 6.5" (which is a little bigger than your stock crank pulley) and usually gives 3-4 psi depending on your combo. Guys swap crank pulleys instead of the blower pulley to keep the warranty intact. As soon as that seal on the blower pulley is removed, your waranty is void.
If you want even more boost after the F150 pulley, you can call up ASP and have them make you a custom crank pulley. A guy on
www.novipower.com was running a 8" ASP crank pulley and he saw
15 psi through aluminum heads and aftermarket intake !!! With the ability of ASP to make custom size crank pulley's, you can run however much boost you want (up to 15 psi) without voiding your warranty!