My OEM Cat is pretty rotted in my 96 Ex coupe so i was thinking of replacing it. After seeing how much an OEM cat is i've decided im much better off buying an aftermarket/ebay Cat.

Im have stock headers/stock cat/Yonaka cat back on the car right now and i like how it sounds, deeper than stock but and not too high pitched at throttle.

My question is: how much louder is an ebay cat going to make my car? my car isnt throwing a cel for the cat but its rusted and making noise when i drive.

Also

Could my rotted cat be the reason my mpg's are so low (24 city/32 highway)?
or could it just be the fact that my engine has quite high mileage? (322k miles)?

 

it really shouldn't be noticeable compared to your muffler and resonator


depending where its rotted, it could still be clogged and messing up engine performance, including MPG. I would say its more likely tho that your engine is tired