well, if the cat is hollow its going to smell more like gas. is this car turbo? im just asking that based on your Diy manifold statement. if its a turbo car that is a whole nother set of variables lol. does the car have an adjustable fuel pressure regulator or anything like that?
maybe see if you can borrow a wideband from someone just to get an acutal number as to what the fuel ratio actually is