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Thats the smell of having no cats on the car, its normal.
Cats burn off alot of the pollution etc left over from the combustoin cycle, along with any unburnt fuel. Without the cats, you are smelling all of this exiting your tailpipes.
If you just put it on, it's gonna stink for a while. It's the "new" burning off of it. Any new mufflers or mid-pipes smell for a few days after install.