This is a set of PI (power improved) camshaft a for a Mustang GT. They were factory components in the 99-04 engine, but are a performance upgrade over factory for the 96-98 engine. They are used but are in excellent condition! 

One difference between the non-PI and PI heads is the camshaft profile. The non-PI heads came with a camshaft profile of roughly .480 inches lift on the intake and exhaust side. The valve duration at .050-valve lift came in at 204 degrees intake, and 208 degrees exhaust. 

The PI heads upgraded the cams to .535 inches lift on the intake, and .505 inches on the exhaust. The duration fell to 192 degrees on the intake, and 184 degrees on the exhaust. This combination yielded a very nice improvement in low- end torque and flow across the board. Both cams are compatible with all three cylinder head designs.