I have 4" and it's plenty for me. I like it and the sound.

 

I think 5in sounds deeper but doesnt show its full potential till after a turbo upgrade.

 

4" exhuast will flow more then people think. Theres a 12v truck around here that has close to 600 at the wheels on a 4" exhuast and his EGTs are kept in check. So unless you plan on going that high in hp, I'd say get the 4". With no other mods 5" would be a waste of your money until you really started mod'n the truck.

 

With a stock Cummins the 3" is fine. You don't need more until 350hp or so. The turbo is the biggest restriction.
If you are planning more mods then 4" is fine to 600+ hp or more.
Put your money on injectors and a box first. Well, after guages of course.
If you want some sound changes, remove the muffler and go straight pipe till 350hp.

 

definitly go with five inch much deeper thoatyer sound in my opinion sounds much better.

 

i read on another post here at DTR that unless your produceing more that 500-550 horse you only need 4, the 5 will cause longer turbo spool.... at least thats what i read.

 

I'd buy based in price. 4 or 5 will both work just fine, but if the 4" you want is 350, and the 5" is 400, then is it worth it to you? Personally, I wouldn't mind spending the extra fifty bucks. Much more than that and I'd just go with a 4" exhaust.

 

I have the 5" Silverline. My truck sounds like a piece of farm machinery going down the highway. It's awesome.

02 2500 4x4- 113K miles
5" Silverline
Quadzilla box
K&N
35" BFG Mud Terrains
FASS 95

 

I also have the 5" and it must be my age as the sound is wearing on me. I have a 5" Donaldson muffler waiting to go on once the slushy weather is gone. I hate getting dripped on while trying to work under the truck.

The larger exhaust will help your temp if you get used to the sound. I actually think the sound is less since I have done my tranny as I can keep the RPM under 2000 easier. At 2000 RPM is when the exhaust note is very penetrating frequency.

 

go 5 man, mine sounds like a MACK truck

 

Thats a true statement. I bought a 4 inch straight pipe kit for my truck a year ago and love how it sounds. A friend of mine has had 5 inch on his last two cummins trucks and they sound really good. He also sell parts and can get me a really good deal on a 5 inch straight pipe kit with a tip. So now I'm looking to buy one off him. Now my truck is stock but I just love the sound of the 5 inch pipe. I do plan on adding horsepower to my truck later on.

 

As far as the need goes, 4 inch is plenty. If my 475 ISX cummins can run a 4 inch down pipe, so can our trucks. With that said the 5 looks awsome and IMO, has a deep sound that i personally like. Its pretty much whatever you want and like. Tim