does anyone make a exhaust system from the turbo back that is 4"? does mbrp make such a system?

It seems that I have seen a true "turbo back" system, but I cannot recall the manufacturer. My MBRP is downpipe back.

Diamond eye does if you get the turbo-downpipe with their what the call a turboback kit. I've been told that its really not worth it, unless your doing some type of turbo upgrade.

Are you wanting a TRUE turbo-back kit, or what most manufacturers consider "turbo-back?" I would start with a MBRP S6004409 which will actually bolt to the down-pipe. This system is more than enough for 99% of people out there. If you feel you need more, you can always install the Diamond Eye down-pipe later.