T-100 Catalytic Convertor Removal or Not?

Gave my 1997 T-100 4x4 to my 16 year old. He loves the truck, but wants more power. He put a flow master on it and now want to remove the cat as he thinks he'll get more hp. No emissions to worry about. I'm worried it will harm engine. Will it work and will it hurt the engine?

If you reduce all the back pressure, he will lose the lower end torque.