This attack's Base Power is anything from 1 up to 150 making it a very powerful attack to be used. However, this is completely dependant on your Pokémon's Speed as well as the Speed of your target. First, the user & targets speeds are claculated. Their Speed Stat is taken into account as well as other effects such as previous attack effects that my have raised or lowered speed, whether the Pokémon is Paralyzed and whether or not it is holding an item that lowers Speed such as the Power Items used to train EVs or an Iron ball.
With these statistics now calculated, a simple equation is made to determine the base power of the attack
Base Power = 25 * (TargetSpeed / UserSpeed)
With this equation, it is very easy to see that if the user has a considerably lower speed, due to being a slow Pokémon or just being unlucky and having had loads of attacks that have lowered speed used on it as well as being Paralyzed and holding an Iron Ball, it will do considerable damage. However, even if the Base Power calculation obtains an amount that is greater than 150, you will never have more than that.