they are the same LENGTH, but the 03's and a lot of 02's use an exhaust donut gasket to help them seal. The 00's, 01's, and early production 02's didn't use a gasket.
So i've been looking at Y pipes on ebay and the Y pipe off my 2003 ZX looks a lot like the Rev y pipe with a Donut, heat sheilds, and all. Can anyone tell me if the 2003 ZX and Rev Y pipes are the same?