You can use that kit with stock gvr4 piping and it would cost alot less. One thing you need to remember is not core size or "top of the line quality" bs but you need to look at pressure drop and stuff like that. Thats why I said if you want a real flow thats been proven and flows worth a shit it will cost around $750. If you wanna use a cheap hack job I'm sure there are plenty kids on this board that can help you with that route.