when you see any box, manual, ad, etc... of 45x4 0r 50x4 that is peak power, when a manufacturer tests the decks at their facility the use a steady stable 16+ volt power supply to the unit, that is where they are able to legit state the 45x4. Any vehicle runs off of a 12 volt power supply via your car battery, so there is no way for you to get the maximum power output from the receiver unit. At the vehicles 12 volt power supply to your stereo you will get between 15 and 20 watts rms. If you want more power you need an external amplifier.