OK so I've been told by person here and there that for a 95 Celica GT, if I put headers and a catback exhuast on it that it won't pass emmissions. Does anybody know whats up with that? My dad and I thought up the idea that we could bore out the stock headers also but somebody told me thats not a good idea cause the headers would be to thin for the heat and it would crack or something like that. If anybody has info on either of these questions let me know. Thanks. And happy new year everyone.

it depends on your state emissions.

in california the celica has a catalytic converter built in the down pipe of the header. So when you replace it with an aftermarket header it will fail emissions.

is there any way to have aftermarket headers and still have two cats? or am i talking non-sense?

There would be no reason to. You wouldn't run your tap water through two brita's. Toyota engines are clean as it is anyhow. If your state only requires one then one is all you will need.

Do not bore out the headers. your friend is correct. all it would do is make ur headers crack down the road from the heat and having no structure.
In CA, if a cat is removed, it must be replaced by another cat in the same place, and has to have a EO as well. such as, if u got a header in the cat and after the flex pipe, u cant just put 2 cats in the flex pipe instead to make up for one not exisiting in the header. check ur states emission laws to see wat they say, thats the best way to check bro.

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so, no headers in Cali. yep...