ok heres the deal. the flowtech shorty headers i bought would not bolt up to the rest of my exhaust. i had to take it to a muffler place to get a custom y-pipe built and its kinda ****ty. anyone know what would be the effects of hooking up 3" exhaust all the way back to this ****ty ypipe? the y pipe is probably 2 1/2", would that hurt performance going smaller to bigger? or should i get a 3" ypipe (if there is one that will fit my headers). Thanks for your input. i want to hook up stock 4th gen cat back up too. i dont have a cat. How big is the stock 4th gen pipes?