2.5 to 3in downpipe to 3 inch exhaust VS 3in downpipe to 3inch exhaust

[Keith320ISTurbo]

I'm getting a down pipe made up with a wideband bung and it will be 2.5 flanged to 3in to my 3in exhaust.

I was curious if there was any benefit to a full 3in downpipe to a 3 inch exhaust VS a 2.5 to 3in downpipe to 3 inch exhaust?

Any real gains or benefits to either?

[chikinhed]

What turbo and other specs? What whp are you at now?

[Keith320ISTurbo]

Honestly I couldn't tell you anything except its a Roto-Master by Rayjay turbo and I posted a pic below of it.
http://carphotos.cardomain.com/ride_images/4/239/1929/38095964002_large.jpg

I'm running K-Jet CIS with not too much modification besides the century/bae turbo kit. There is a under the hood intercooler and HKS BOV added. I'm on 9-10PSI right now.

And here's a picture of my set up to give you an idea of what the century/bae kit looks like.
http://carphotos.cardomain.com/ride_images/4/239/1929/38095964001_large.jpg

[GazM3]

im no exhaust expert but i know fluid dynamics and the exhaust gasses leaving the turbo will take up the most specific volume cos of the heat so if anything u want the dump pipe at least the same size if not larger than the rest of the system rather than smaller. I guess one would need to know power level ect to determine whether the 3" main exhaust is the correct size also

[tlmitf]

Best bet is to step it up right off the housing.

The gas is swirling as it leaves the turbine, which is bad for flow.
Stepping the dump pipe up sharply creates some turbulence, which sounds bad - but turbulent air actually flows better than a rapidly spinning vortex.

I was privy to some testing with vanes inserted into the dump pipe to 'catch' the spinning air, turn it, and shoot it down the dump pipe.
Results were mixed, and generally we found it was the crap dump setups that gained from it...