There should be a power setting on the control panel for Maximum. Other than that I don't know.
I don't think you'd always want it to run at Max speed. It would eat up a lot of electricity for one. It would also keep the fans running at full speed all the time, and may build up too much heat and eventually cause damage. Part of the energy savings is that if you're just browsing the web, looking at pics, etc, the CPU doesn't need to be on full blast.