I have been working on getting my Spoon 4-2 header on my 2000 civic Si,the header was originally intended for a EF9-so when I tried to bolt it up to the stock Si downpipe the flanges are different,the front hole lines up the the side ones do not.

I am going to assume the Si uses a larger downpipe than EF9 B16A's do-anyone know off hand anything US spec that's the same as the EF9 downpipe and as far as downpipe primary's go are all stock B-series downpipes smaller than the Si ones?