Man what a question. I guess what came from the factory would be safe,after that who knows ? Maybe 400,500,600H.P.the skys the limit.Are you looking for dependable street use or all out drag racing? Ihave seen 600 plus on turbo go low 9,s and drive to moms house for dinner.Do your home work and keep asking questions untill you have the answer that you can live with.Good luck.