He obviously isn't into SPL or the roof and glass would have been reinforced.
I could be 1700 watts if its rated for competition as I think the output is rated @ 4 ohms. If we has loaded them down to 1 ohm or less them it could actually be pushing a heck of a lot more. Plus the car looks way too small to be running 17K. I do stage rigging and 17K could do a decent sized concert!
I used to be crazy into systems like that when I was a kid and had my small hatchback kitted out the same with a wall of 4 x 15" behind the seats. You could actually feel your ear drums moving.