The drivetrain loss is really low.

The McLaren 720S is a familiar sight in drag racing videos on Motor1.com, but in a new video from Hennessey Performance makes the supercar put up or shut up by placing the machine on the dyno. The clip is a great chance to hear the 4.0-liter twin-turbo V8, too. 

According to Hennessey's dyno, the 720S produces 675.8 horsepower (503.94 kilowatts) at the rear wheels. Unfortunately, the graph doesn't show the torque rating.

Gallery: 2017 McLaren 720S First Drive

The 720S' V8 makes 710 hp, according to the factory figures. This translates to a drivetrain loss of 4.82 percent from the engine to the road. The expected drop is in the 10 percent to 15 percent range, so this is a mighty impressive figure. The low drivetrain loss could be due to McLaren underrating the V8's output, or the firm's seven-speed dual-clutch gearbox might be especially efficient at sending the engine's grunt to the wheels.

The 720S sounds absolutely amazing, too. At lower revs, there's a musclebound roar. When the rpm climbs closer to the red line, more of a high-pitched howl joins the bass notes. While the coupe looks cool, it'd be hard not to pick the Spider simply for the chance to hear this noise better.

Hennessey's site currently shows three levels of additional tuning for the 720S. The HPE800 pack includes revisions to the ECU, air filters, and exhaust. The HPE900 adds upgraded turbos and intercooler to the improvements. The top-dog HPE1000 further packs Motec engine management, stainless steel headers, high-flow wastegate, and revised transmission.

Source: Hennessey Performance via YouTube