All brands about the same there I is only one real size....factory is 3.5 inch and pretty much anything aftermarket is 4 inch but not squished and mis shapes. Get a 4 inch down pipe and 4 or 5 inch exhaust flo pro is probably the cheapest but most on here seem to run mbrp... I run a magnaflow myself. But if your straight piping it there really is little to no difference in any kit that you purchase other than quality of metal and most kits have options on what metal you would like to pick.

 

Stock is 3.5 i think but it's all crimped. All the kits come with a 3.5 ecru a few. You have to make sure you get the 4 inch down pipe. I think the outlet for the turbo is 3.5 so having a new pipe that is straight is good for it. The 4 inch is just over kill

 

Almost all kits come with 3.5" regardless if you get a 4" or 5" exhaust. I have a 4" Diamond Eye down pipe to 4" Grand Rock exhaust.

Stock vs. 4"

 

my 05 has a 4" diamond eye down pipe to a 5" exhaust to the end.:nod:

 

Actually, the stock DOWNPIPE is 3". The after the cat, the factory exhaust is 3.5". Aftermarket exhaust systems will have either a 3.5" or a 4" downpipe. There will be virtually no difference in power between either one. The 3.5" downpipe is easier to install due to the tight work area so that has my vote.

 

The outlet for the turbo is 3.0 or 3.5. Having the 4inch down pipe is nice though. I got the mbrp 3.5 to 4 and about like a year later i switched to the 4down and 5inch. I like it a lot more.

 

As mentioned, the factory DP is 3", not 3.5".

A 4" DP will fit, but it'll be really tight and a lot of people have had the pipe contact the frame, firewall, etc and swapped it out for a 3.5".

Performance wise, you won't notice a difference between the two and I'd recommend the 3.5" in 409 stainless steel.

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Thanks for the help guys

 

I have the Diamond 4" down pipe and it has a better design as far as making the turn to under the truck. Has a softer turn and it does even look better then the Magnaflow. I have had both but as far as performance goes you won't make more power with the 4" but it does move heat out a bit better. But it also probably makes the turbo spool up from a idle a little more sluggish because the exhaust is moving slower through it.
I like the looks of it and I have it mainly for flow reasons.

It is a special order item and even if you buy a exhaust system that says: 4" Turbo Back System ........you are going to get a 3-1/2" DP

GO FIGURE???? Made me mad lol