On my 04 i wanted to stay true and do an actual 4" fwi... to have a true 4" it takes a bit of time and finagaling... u can pick up either a 3 or 7" cone and as for elbows you WILL NOT find a flexible 4" elbow unless ordered off of the interent... i used 2 or 3 hard 4" 45 degree elbows and the roof flashing you can get from any hardware store... the hard part of a true 4" on an 04+ is the MAF... the way i did it was to use some sort of rubber extension and use it to attach the maf and intake manifold... then use a 3 to 4" rubber converter piece and run your 4" pvc off of that... makes a hell of a roar... good luck... might get picks up for thos interested in a true 04+ 4" fwi