Originally Posted by reelbb

Coming from a 2GS guy, the reason for the third cat is that Lexus certified the SC as a ULEV or an Ultra Low Emissions Vehicle. The third cat just scrubbed any excess gas that came from the primary cats.

On a GS430, I was able to test a custom downpipe with some mandrel bends vs the stock 3rd cat downpipe. The result was a 2hp increase to the wheels, keep in mind the GS exhaust is a straighter shot than the SC.. I intend to remove the 3rd cat and resonators in the next few months. But I think the best method is to buy the megan downpipe off Ebay and some exhaust gaskets, that way if you don't like it just swap it back and resell on ebay for a marginal losss.

Gutting the 3rd cat and resonators would be a huge mistake in my book, it's a very expensive and hard to find part to replace. On a side note, when I sold my GS, I placed my OEM pipe on the curb for large garbage pickup and it was gone the very next morning. My neighbor told me a scrap guy came by and just threw it in the back of his truck, I'm sure he made a quick 100.00 at the scrap yard for the platinum in the cat. :-(