Do they actually add horsepower??

[-EnVus-]

I thought about a few things that made me question if they add horse power so i decided to ask. Also, I apologize for the questions, but I just wanted to get experienced answers or supported opinions.

Thanks in advance

1. throttle body spacers?

2. Different gaps on spark plugs, instead of noted specifications

3. lightweight pulleys

Also I wanted to know about performance of a chassis C-pillar bar; does it really make a difference

thanks again and reps will be given to any assistance

changing pulleys is the only best thing to gain