Here is more information from Top Gear:
Zonda HP Barchetta, first seen last year, has a 6.0-liter biturbo V12 on board with 789bhp, the same effect from the wild Huayra BC. It is matched with a six-speed manual transmission, along with a mechanical lock diffuser and rear-wheel drive.
It also reflects BC's suspension design and has massive brakes: 380m ventilated discs around with six piston caliper front and four piston caliper at the rear.
A nice touch is what these monster brakes hide: The 20-inch and 21-inch rear-wheeled aluminum wheels have different color posts left and right. all about details with Pagani.
And the best part is if you do not want to drive your new Pagani, you can always hang it in your living room.