I'm a newbie so bear with me. What does PI mean and how do you tell the difference. Did they come on different year models?

 

PI stands for "performanceimproved" and they came on the 99-04 Mustang GTs, and NPI stands for "non performance improved" and they came on the 96-98 GTs and they suck. I think if you look at the ports on them I am pretty sure the ports on the PI heads are bigger so as to flow more air and improve performance

 

They are bigger on the PI heads. Also, the PI port shape is more of a square, where the NPI is a circle. That's how you can tell if you don't have the two to compare them.

 

Is the allumium crossover the part in the front where the Thermostat is? If so mine must be stock.

 

PI is Performance Improved and NPI would be Non-PI.

theres about a 60hp difference.