This is a discussion on What to replace my stock exhaust with, only have prodrive oval muffler? within the Builds forums, part of the Tech & Modifying & General Repairs category; Originally Posted by zax
Actually, let me clarify... this is true ONLY for the 2002 and 2003 WRXs. In 2004, Subaru changed the CL to OL transition delay, so running a downpipe without a tune can potentially be harmful to the vehicle.
Ahh.. I was under the impression the change came with the 32-bit ECU. Good to know (not that I will ever be owning an 04-05 WRX).