Cross over pipe diameter - same as secondary?
 

looking at this really neat exhaust system here:

http://forums.pelicanparts.com/uploa...1205434166.jpg
from this thread: http://forums.pelicanparts.com/porsche-911-technical-forum/398050-best-headers-street-3-2-3-0-a.html

just looking at it, it seems the crossover pipe is just slightly smaller than the secondary. So randomly thinking, I was wondering if there is a calculation to determine just how large the crossover pipe needs to be. in my pea brain, i would think it would not need to be as big as the secondary but big enough to balance. from a builders point of view (which i am not :) ) i would think that smaller would be better to save on weight.

any thoughts on this?

thanks!