I want to make a custom "Y" pipe.I have a bunch of 2 inch and 1 7/8 stainless steel tubing. I wonder which size I should use? I'm going to try and match the lenght of the "Y" pipe. I have heard this helps on normally asperated motors to match header lenghts.What do you think?

 

http://www.freewebs.com/subaruloyale/

on mine john left the stock tubing off the manifold. right after the bend is where the new pipe went. with a a very smooth merge where they come together

What gauge/wallthickness is your tubing? If it thinner then 14 gauge (.075 wall) it maybe difficult to weld to the fanges.

The size pipe really depends on how you want your power curve to be... mine is pretty high up there compared to stock (but thats where I keep the engine so it works for me)

 

I run 2.0 from the heads to the cat, 2.25 to the muffler (midpipe) and 2.5 out from the muffler. (all measurements in inner diameter)

I'm strongly considering one of these http://www.discountconverter.com/converters/images/8015.gif for on the ER-27 exhaust when I get to that point, also comes in a 2-1/2" size. Equal length lead pipes, with a cross-connection is the best route for power gains. Any bends in the system, should be as smooth as possible, too.