That's the beauty of hybrid/electric drive, software tuning. Either by revving the electric motor faster or letting more current through the system.

Just like the 918's hybrid system, Tesla built their electric system with a healthy safety margin, for reliability other reasons. Through testing, they can find out how close they can cut into the safety margin without compromising safety and reliability. Porsche did it by re-rating the electric motors, Tesla did the same thing. The difference is, Porsche didn't charge extra for the performance that was already there, Tesla did.

It's like tuning a conventional motor, but without the mechanical work. 


--