Got me, I didn't name the video, but I guess they were calling it a 906 motor to differentiate it from the other six's put into 914-6 GTs and raced (911T, S). I've seen it referred to as simply "the Carrera 6 motor" as well. I bow to others' superior knowledge on what the differences are between all the race motors, as in compression, heads, etc. So I think - guessing here - they called it a 906 motor to refer to the most common engine in that car, the 901/20 engine making 200 hp+