Looking at replacing my stock exhaust system with a 4" from the turbo back how much will it increase the HP and noise level and what other benifits would it have or is a waste of money if I'm going to keep everything stock.

 

Just adding the big exhaust won't give you any more power - you have to inject more fuel to do that and that is accomplished with a chip or a tuner.
What it will do is to free up that rather restrictive exhaust that Ford put on there and go a long way to lowering your EGT.
You'll never notice any difference unless you have a pyrometer.
Well,.......... It will sound a lot better.

 

And then beware the PMS bug.
But I fear that you are already infected with it because you are considering the big exhaust.

 

I don't mean to hijack this thread but which of the 4" exhaust should we be looking at? I don't want to spend the bank for a stainless one. Should I get one with a muffler of not? Thanks in advance.

Steve

 

Muffler is up to you. Some dont like the blab that you get with a straight pipe. Most 4" preformance mufflers are a straight thru design so there is very little restriction in them. Just get a Aluminized system if you live where they dont salt the roads in the winter.

 

An aftermarket feels a tad stronger to me because it allows the turbo to spool up faster, but not any more peak HP really.

I will add that since I have deleted my EBPV 90% of the "flutter" is gone. Actually quietened my exhaust down some too.
I have stock system with straight pipe, and a 5" tipe angled out the back similar to a stock D-max. The sound is nice and mellow.
I think I'm gonna go with a 3.5" dp and call it good unless I really have a problem with egt's. the SS they put on from the factory is good stuff, and costs a pretty penny to replace it.