We've reached Peak Engine Sound :)
 

From the Video description: 

The project for the Huayra R isn't based on any of their production model, while maintaining some of the shapes and lines of the road-going Huayra models. This 'freedom' allowed to significantly raise the development targets for each individual component. First and foremost, the development of the most powerful, naturally aspirated internal combustion engine in the history of the Atelier, called Pagani V12-R. This is a 6-litre V12 racing engine, designed in partnership with HWA AG specifically to meet the brand's requests but also the desires of Pagani’s customers, who dreamed of an incredibly powerful high-performance, naturally aspirated V12 engine for their new projects. It's able to produce 850hp at 8250 rpm and maximum torque of 750 Nm from 5500 to 8300 rpm. Red line is set at 9,000 rpm and the engine weighs 198 kg. Attached to the central monocoque, with which it forms a structural element capable of supporting the transmission system (six-speed sequential gearbox) and the chrome-molybdenum alloy steel subframes, the new engine is exceptionally efficient and easy to run, with service cycles only every 10,000 km. The exhaust system is made from Inconel 625/718 alloy, with tubes one-third the thickness of those normally used in road car equipment, and coated in ceramic to protect the engine bay and ensure better heat dissipation directly to the outside. As you can hear (and spot) from this video, the car can also be equipped with mufflers that could be fitted as required, ensuring that noise emissions are reduced to within the FIA limit of 110 decibels for noise restricted tracks. I honestly enjoyed it so much even if it wasn't as loud as it could be without those mufflers because keeping it more quiet you can appreciate more the mechanical symphony produced by this racing engine (especially the intake sound). But yeah, you know I now would like to record it with the full straight-piped exhaust layout! Thanks to the specific development of the monocoque and the use of new structural principles and materials, the Huayra R has a dry weight of just 1,050 kg.