Will a DCRH from a 02-04 RSX-S Fit a 06-08 fg2 si?

 

nope.

 

so it wont fit in at all? or will it fit in, but you have to mod the exhaust?

 

I don't believe it will fit at all.

Here, look at the stock exhaust manifolds. See how the Si seems to come out almost level from the flange where the RSX comes out and drops down pretty quickly.

Si: http://www.sonshondaparts.com/...ch=no


RSX: http://www.sonsacuraparts.com/...ch=no

 

It wont fit right against the firewall. Check the part numbers, they are different. (plus above post proves it well enough)