"SI/DO setup?" I'm slow on the abbreviations, not sure. I am running a 3.73 rear gear. KM

 

Single in/Dual out.

 

Duh!!! Slow today! Single side factory outlet position did not use the shiny tip.
KM

 

Sounds great inside the truck. A little louder than I would want on my personal truck, but the tone is awesome for an ecoboost, IMO. (your pypes setup)

I can believe mpg increasing because the stock exhaust may have been somewhat restrictive.

 

4” is fine if you want the tone that a bigger pipe will give but it’s complete overkill for any EB truck.

 

eh, single 3" is good for ~500-550whp or so, tops. I like having overhead.

Though this article suggests otherwise for 3" exhaust (single) at ~339hp
http://forums.superchevy.com/super-c...aust-pipe-dia/

 

3.5” is a good compromise. 4” just isn’t needed until 4 figure power levels.

 

doesn't matter until somebody makes a good downpipe option for the 17+ anyways, as it goes into a single 2.5" midpipe before the OEM muffler, which is stupid IMO.

 

Is the factory Y 3” like the 5.0 trucks?

 

Maybe that's why mine doesn't sound too bad as I have the Livernois catted down pipes that feed straight into the exhaust. No resonator. 3" all the way. I also have very little/almost no drone.