Kinda funny how you say it "I did this just for fun"....others would feel blessed to be able to do such a piece. Can i ask... is the smoke edited by you as well? Because i know smoke is hard to do, but i see you changed the rear of the car a bit as well.
Effectively, I added a little more smoke on the original one by picking its color and with a slight transparent brush. First a 200 px large brush with 20% opacity, then a 100 px one with 10% on some areas... but it's really subtle.