The Apexi WS exhaust, which can be found HERE (http://www.coximport.com/store/104-KM01), is only compatible with the Eclipse GS... it is the same situation with many other exhaust.

I happen to have an Eclipse RS, and was wondering if the exhaust system would fit it as well?

I don't know the differences between the GS and RS so I don't know.

Thanks.