Thinking about getting this set up but have kind of a dumb question. The collector size on the headers says 3" and but the y pipe in let diameter says 2.5". Am I miss reading and understanding something here it says this is the suggested y-pipe for these?

 

those are the 2 part numbers if you want Hedman.

If you are actually getting yourself all concerend about the diameters don't worry your pretty little head. They are fine. Read the umpteen threads on the same topic. They are low cost, decent quality and work just fine.

Be sure to get decent gaskets such as Percys Seal 4 Good or Mr gasket dead soft aluminum.