Naruto mixed his wind element with the Rasengan during his training, maintaining its original stability and increasing its power, far beyond that of his ordinary Rasengan. An example of the power that element manipulation adds to the Rasengan is shown when it is tested against Kakashi's standard Rasengan. The fact that it was only partially completed, but still be able to easily overpower Kakashi's Rasengan and damage his hand demonstrates just how far the Rasengan has been pushed when combined with element chakra.