So I figure its about time I tackle the exhaust on my truck. But I've never done a custom exhaust setup and had a couple of questions.

I am planning on the pacesetter LTs and Y pipe. I just wasn't sure if I should stay with the 3" pipe the whole way back or use something smaller after the cat/ mufflers.

 

Stock is 2.5 I believe, are you gonna run duals or just a single?

 

Planning on Single, cheaper and less work.

 

You'll probably be good with a single 3" back. I've heard quite a few people running that and liked it.

 

The headers are probably 1 and change inches port diameter. It depends how you want your truck to sound and what performance you want. 2.5 from the cat back will sound decent and give you excellent off the line power. A 3 cat back will be noticeably louder and give you better top end.

 

2.5 in pipe is too big for true duals ! I would use 2.25 in pipe all the way back ! It will sound good and create enough back pressure so it flows even !

 

For a truck, 2.5 might be a little on the large side.... but, all that would result is a bit less bottom end torque. Bump to a 408 though, and I think it would be perfect.

 

Unless you're running 400 cubes or larger, 2.5 would be a tad too big.

 

3" to the cat then 2.5 for the rest of the single pipe system. 2.25 is max for a dual setup.

 

I'm interested in this also.

I've just done the intake side of my 5.2, and have Pacesetter LT's and Y-pipe (3") in the shed waiting for the rest of the exhaust system.

On my list is;
Magnaflow 99559HM 3" Cat (12" long)
Magnaflow 12279 3" Muffler (5"x8"x24" long)
These all sit further back than standard due to the LT's.

With a regular cab & short bed, this puts me close to the axle (about where the tailpipe starts).

It was the plan to continue with the Magnaflow 15035 3" tailpipe (pass side rear exit), with a 35107 4" Tip.
This by the way is the only Magnaflow pass side rear exit (my stock location) option for 3.9-5.9 magnums.
To go to 2.5" it is pass straight rear exit (not my location of preference).
The dual rear exit is also 2.5" off a 3in/2x2.5out muffler.

I did loose a little bottom end torque with my inlet mods, but am hoping to regain some with the headers and exhaust, to balance the out flow with the in... at some point I'll also do H&S1.7's.

So, whilst I've been told 3" all the way will be good choice (and that is what Magnaflow offers), I'm a little concerned about loosing more bottom end, rather than gaining some back.
At the moment, under 1600rpm is a little snoozeville, but by 2000rpm it comes to life.
Remember, I'm manual trans, so don't typically rev as hard working up the gears... 2000rpm is the regular driving shift rpm.