Without seeing code for smoke generation and for the smoke, it is hard to give a great answer, I suggest checking to see how many smoke entities you are creating. Are you creating 1 per game tick? Creating a bunch of entities needlessly will wear on frame rate. Also double check the code on your smoke entities is just a simple timer, and not anything too complex.

Please share a code snippet so someone can review and see if there's another issue causing the frame dip.