I have a 99' SC400 and I’m wanting to make my exhaust sound more aggressive.

1. I was thinking of coming 2.25" from the cats into a X-Pipe & running true dual exhaust back, deleting resonators and mufflers....

2. Same as above but instead deleting the cats and starting from the manifolds. My only concern is getting a CEL & smog issues seeing that I live in California.

So my question is will deleting the cats give me that much of a better exhaust note that will make dealing with smog problems worth it?

And having a CEL is not an option at all....

 

I don't think deleting your cats would be worth it, no but this is especially the case in Calfornia. In stock form that exhaust system does pretty well with the cats.

You'd need a lot of heavy engine modification to start hitting restrictions with those cats unless you went VERY far down that road with a fully built engine and custom twin turbos or an Eaton M-90 roots supercharger with a fully custom tuned aftermarket ECU there is no benefit performance-wise to deleting the cats.

You will definitely get CELs without cats and if that doesn't automatically keep you from passing smog testing then the tailpipe numbers on the smog dyno rollers certainly would.

Plus, the factory engine ECU will assume there is an issue without the cats in place and thus could mess with the fuel & air mixture by going a bit richer than normal to compensate for a component that it expects to be there... all of which would only make the tailpipe numbers worse.

Technically you should be able to stay legal if you only modify anything *before* the catalytic convertors. This means you should be able to perform a resonator delete and run some more aggressive mufflers. From the stock cats on back you could have a fully custom system made or you could just have a shop delete the resonators and then you could select whatever off the shelf catback system that is available for SC's.

Just doing one or both of those things will completely change the sound and character of your exhaust. You've already got the desirable 290hp/300tq version of the 1UZ and with the improved sound will better match the car's acceleration capability.

 

The cats serve a very good purpose (environmental) as well as the practical ones Kahn mentioned. It would be foolish to delete them if an improved exhaust note is the goal, as the SC400 can sound gnarly good with aftermarket axleback mufflers and custom center section (deleting the 3 resonators). I went with a simple y-pipe replacement, no x- or h-crossovers. I've got a couple neighbors -- Chevy muscle cars and BMW M-series -- that always marvel at how aggressive it sounds. If it's enough to impress them, it's sure to satisfy most people.