breather filters
 

Will removing the air hose that leads to the left valve cover hurt performance. What I thinking of doing was getting a breather filter for the valve cover would this hurt or help?

it will help to keep the hot gases and oil from getting into the intake. i used breather on both my valve covers and deleted the egr system the truck ran alot better afterwards but this isnt emissions legal at all.

Could I do this on my 04 cobra if so how hard is it? Do I need aftermarket head covers??

honestly you dont need to do it and it wont do much for perfornace if thats what your thinking. i would leave it alone unless you have oil consumtion problems liek my 4.6 f150 had.