Will opening up the exhaust (free flowing) too much hamper low end torque/drivability?
Or is a certain amount of backpressure needed.
I'm particularly interested in how backpressure would affect my 05 Suburban 2500 6.0L

 

Opening it up will help a little bit, to an extent, then it will start to hurt things. Are you talking about just a catback, or a full setup, LTs off road intermediate pipe(s), etc...?

On my 6.0, I am running a full 3" system, from the collectors to the merge after the stock muffler. I stepped it up from the stock manifolds (going to LTs typically hurts TQ just a little, but HP gains offset that). My stock intermediate pipes were 2.75", so going to 3" isn't that big of a jump. Plus I have a cam that makes a pretty good amount of TQ, so I can't tell you if the move to 3" affected anything. As for drivability, you'll be fine.

 

You want to keep a lil bit of back pressure on a NA setup.. when you start getting into FI is when you want free flow, due to the chambers getting stuffed with fuel,air.
I am sure that a true 2.5 inch dual set up on your 6.0 or a single 3 inch would suffice fine, unless you are making big hp(400+)

 

I use my rig for recreation. I pull snowmobile/ATV trailers, boats (the toys).
Not heavy stuff, maybe 4000lb.

My previous truck was a 95 Chevy 5.7, this Suburban has way more power but like all of us I want more.

I have installed a set of ARHeaders 1.750 primaries, 3" collectors with cats. System has duel 2.5" pipes going to the muffler. Over the weekend I installed a Magnaflow cat-back which has duel 3" inlet and single 4" outlet.

When shopping bolt-ons I look for things that increase low end torque, figure that should help drivability and MPG empty or while pulling

Since the Magnaflow is a open design I was getting concerned I may have opened the exhaust too much, but all seems to be fine. Truck sounds good.