I know 3" is pretty common. But two 3" pipes going into one 3" pipe doesn't make a whole lot of sense to me.

I plan to be running around 375 rwhp now plus some nitrous in a few months. Currently have a 3" system, headers going on in a week or so. I was thinking 2.5" or 2.75" y pipe. Duals are out of the question right now.

 

That's why I like two 3" pipes going into a 4" collector. That DOES make sense.

 

Try to get a nicely setup Y as well like the quicktime ones. The smoother the bends and the better the collector should help to lower the rasp.