I recently bought a cat with no air tube but my car has a cat with an air tube on it how will this affect my exhaust with headers and borla cat back if I put this new cat on?

 

The cat will work just fine without the air tube and your car should be fine. But you will not pass a proper visual emmissions inspection.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

But does this change my emissions on the sniffer?(less or more)

 

I have a 3-way air Catco converter WITHOUT the AIR hooked up. I passed with flying colors in CA. With a properly tuned car, I would say you should have no problems.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System