no, no, no, no, no and no.
babies are not ready to switch to forward facing until they are 20 pounds AND 1 year old. and even then it is not neccesary. your baby may be big but being a bigger baby when he is that young would make it even more dangerous to turn him forward. his neck muscles are not developed enough to support his head in an accident. and because he is bigger, his head is most likely bigger as well, which means that it would be harder for him to support the weight. if you did get into an accident he would either be seriously injured or killed.
and you would also probably be arrested for child endangerment if you got pulled over. they have convertible car seats that you can use. these go up to at least 40 pounds and will still work when your child is old enough to be turned forward.