Whoopsy:

Why the pop up hood for 911?

Conventional cars NEED a pop up hood in order to gain some clearance for the hood to deform, saving the person from hitting the hard engine block.

Last I check, it is EMPTY SPACE beneath the 911's hood, there is no engine block to bang your head on.

 It has to do with where (specifically, at what height) the car hits the pedestrian, and how said pedestrian rotates or tumbles onto the car, and consequently where his/her head hits. 

My knowledge of the issue is very limited, but it would appear that cars that present a tall, straight front end to the pedestrian cause less injury (apparently, that is one reason for the higher front ends on the newer BMWs).

Sports cars with very low front ends are at a disadvantage wrt the regulations. That would explain the need for a pop-up hood. This is actually good news, cost and complexity aside. For the last several months, I've been wondering how ugly a higher, flatter front end would look on a Porsche, or on any mid/rear engined sports car for that matter...

Kamal