Let me start this off by saying I dont know jack about cars. What does it mean when I read that the 03/04 cobra's have a 4valve engine? what is the difference between the 03/04 cobras, 03/04 GT mustangs, the 05-07 mustang gt's, and the 07 shelby as far as valves are concerned? What does the number of valves have to do with your cars performace? Thank you for taking the time to explain this to me.