My cats were rattling up a storm on my sc400 for the past week, so I figured I would just hollow them out. The top converters emptied out real easy and made the sound nicer, but the center cat has proven otherwise. I decided to try and hollow out the center cat and from the beginning i could tell that it would not be a quick empty out.. After about 4 hours of hammering I gave up and now have a destroyed, useless center pipe. Just spent $250 for a new one! Yaaaaaaaaay

So long story short, if you wanna hollow out your cats, go ahead, it will sound better and I haven't gotten a check engine light yet! but DO NOT TRY TO HOLLOW OUT THE CENTER CAT. You will just be left with a metal blob at the end of the pipe, blocking your exhaust flow.

My sc3 had a cat with metal instead of ceramic like normal. Much harder to hollow out, but it is do-able

Just gotta be patient and take your time. Ive done it.

Altho, I dont even have cats now.

Do you get worse mpg without the front cats?

I didn't notice a difference between the hollow cats vs the 2 new cats.

yeah, the center cat is like solid metal, i couldnt get it to come out more than a few crumbs, but i think bits of my top 2 cats are caught in the inlet of the center cat, making it harder to break up, so im just waiting on my new center pipe

Hollow out the primary cats, and just cut out the center one. Have a cheap exhaust shop put some straight pipe there. The center cat is usless and wont throw any codes since its down stream of the O2 sensors.

I think im going to hollow my primary cats if theres no mpg change.
It wont throw cel right.

What did you use to remove the mateial from the primaries? Just a hammer and pipe or did you drill them? Looking to do mine but just wondering how much time I should plan to get it done. I've had some that come out easy and some that you wish you hadn't removed.

I gutted my front cats with a drill with a long 1" spade bit on it. Took me all of 40 minutes, and that was only because the car was on jackstands rather than a lift.

So you left them on the car? I'm planning on pulling them off just because I go some new gaskets to fix the leaks I have. I can't stand exhaust leaks, one of my pet peeves. I'm debating on whether or not to make my own pipes and scrap my cats for money or just hollow them. Lextreme sells the upper flange but I don't have a welder at my house, I would have to take the pipes to work and weld them hoping that I get the clock angle right.

Yeah, I left them on the car. If I was taking them off the car to do it, I would just weld up some straight pipes, but I took the easy way out as I plan on long tube headers sometime in the future when I'm not broke haha

i used a 4 foot long pry bar and just jabbed in there untill it was all out. it comes out easy.