4 seam added velocity?

Hi, I’m a 15 year old who’s fastball tops out at around 76. The only fastball I thorw is a 2 seam and that’s because I get a decent amount of movement on it but will throwing a 4 seam add velocity to my fastball? I want to keep my primary fastball as a 2 seam but it wouldn’t hurt to have a pitch that I can throw just a little harder than my 2 seam. How many extra MPH’s, if any, would be added with a 4 seam? It sounds like it would add around 2 or 3, is that true? And why?

In theory it should, but I would recommend the grip you feel the most comfortable with. As for myself I throw a 2 seam.