Ws on transcript affecting admission to engineering masters?
While it is impossible to know what is in the minds of an admissions committee, I would think a few W's shouldn't matter much as long as your GRE scores are strong and your letters are positive. However, I would consider briefly addressing those withdrawals in your personal statement in a positive way (ie, you preferred another course vs you hating a course). 

Basing this on a brief stint on a medical school admissions board in the USA.