The 2005 - 2009 Mustangs were meant to be throwbacks to the 60's fastbacks. So the front spoiler and hood scoop, both made by Cervinis, work great. I stumbled on the diffuser. Whether it does anything is hard to say. It's supposedly wind tunnel designed and extends forward, almost to the axle, with an upside down spoiler on it's leading edge. So you could say it prevents the airflow from going through all the junk under the trunk. Wind tunnel vids I've seen show they do clean up the airflow coming off the back of the car, which reduces drag. I just though it looks cool. And I've never seen another like it, just all those short fin wannabe diffusers that vehicles come with, that obviously don't do anything. I have to watch it backing up to curbs, and parking lot blocks. It's carbon fiber and cost me $1000.00.
Hardest thing I did to it was cutting the long holes in the hood for those carbon fiber vents.