[sunrat]

Originally Posted by S14DB

On a S13 this is true. On the USDM S14 they changed the exhaust manifold and put a close coupled cat in the down pipe. This is why #4 has the big box on it by the manifold.



#5 is a hollow shell of a cat. It was easier to just make empty shells than another short pipe. Tap on it with a hammer, you will hear it's hollow.



If #4 isn't rusted and only 9+10 are then just toss 9+10.

Thanks for the info!