92eg_b16

yeah i got a b16 swapped into my eg. the exhaust recently got disconnected from humongus speed bumps where im from, but i just changed the oil. let it run for a minute, checked the oil. the cap, filter, and plug are all on, but when i took it driving down the road, it started smokinng bad. looked under the car, it was coming from the cat. I took the valve cover off when it cooled down to check the valve gasket, it was fine....
what other possibilities can it be?