Many players lose power on their forehand because they contact the ball too much in front of the body. This means they aren't really rotating into the ball with maximum efficiency – instead, as they are about to contact the ball, they are using mostly arm, which is moving forward while the body lags behind.
Instead, try contacting the ball more to the side of the body, by your right leg (for righties). Imagine there's a rod going through the top of your head, and circle the rod, as Ma Long does in this 48-sec video. By doing this you'll naturally rotate into the shot, getting maximum power and efficiency. This is true for both looping and regular drives.
Note that the goal here isn't just to get lots of power; it also leads to better control since you'll be getting the same amount of power (speed and spin) but with less effort. The more effort you have to put into a shot, the less control, so develop efficient shots where you minimize effort while maximizing power.
Here are the forehand contact points for these players – or choose your favorite player and Google that player's name along with forehand loop pictures.