I think that there is no real evidence to support the idea that smoking can improve singing. Smoking has been shown to have many negative health effects on a person's body, which definitely affects their ability to sing effectively. Furthermore, studies have found that smoking can actually decrease lung capacity, which would make it harder for someone to produce good-quality sound while singing. In short, smoking is probably not going to help your singing voice very much, and may actually end up harming it in the long run.