Hey guys been trying to find the exact opening diameter for a stock 04 mid pipe but i just seem to not find any. Cuz im looking at getting an aftermarket y-pipe that is exactly the same diameter as the mid pipe inlet so as to have perfect flow.

My plan is as follows: stillen hfc -> stillen y-pipe-> stock mid pipe -> aftermarket muffler

Only concern is the stock mid pipe! or should i just stay stillen hfc->stock y-pipe->stock mid pipe-> aftermarket muffler. The reason why im dying to change the y-pipe is because everybody claims its the most restricitve after the cats. So what u guys think i shd do? thanks

 

2.5" inlet.