I'm wanting to run a straight pipe inplace of the cats until I can afford buying a full exhaust (I'll be making the pipe myself) and there is a line running from the front pre-cat and one from the main cat. I was wanting to just replace the 2 pre-cats, but I don't know what the line is, so the question is, what is it and do I need it?

Attatched pics of what I'm talking about....

Thanks.

 

look up racing beat I think that small tube opens up the ports

 

not on a GS..there are no ports to open

it comes fromm the air pump to bring fresh air into the cats to let them burn more effectively.

 

That's what I was thinking. Thanks.

I decided to just knock out the inside of the cats instead of making a pipe. Much easier and cheaper.
Though I still might replace the main cat with a pipe, since in order to knock it out you have to drill it or cut it open. AKA, too much work.
After seeing what my car had to breath out, kind of makes me feel sorry for it.

 

What is the similar line coming off the main cat?