The Senna has active aerodynamic winglets inside its front bumper, on either side of its radiator grille, as well as that high-altitude active wing across its rump. And yet, when running in Race mode (when its adjustable suspension drops the ride height by 39mm at the front axle and 30mm at the rear), more than half of its downforce comes as a result of ground effect.
The management of so much downforce was always going to be the key challenge in making the Senna drivable on track. You needn’t know much about the history of motorsport, after all, to know that cars with lots of aerodynamic grip can be treacherous on the limit. But the Senna balances its downforce automatically, as you accelerate, brake and corner, by adjusting the pitch of its active aerofoils front and rear.
More important, it also adjusts the car’s RaceActive Chassis Control II active interlinked hydraulic suspension by degrees, adapting the levelness and pitch of its body all the time and, resultantly, the distribution of its weight and effectiveness of its underbody aero.
Above 155mph, that rear wing actually begins bleeding off downforce to preserve handling balance and stability – and in order to prevent overloading the car’s road-legal Pirelli P Zero Trofeo R tyres. Under heavy braking, the front bumper winglets also flatten out to bleed off front axle load, such is the effectiveness of the car’s front splitter under dive.
Under its all-carbonfibre bodywork, the Senna is constructed from an evolution of the 720S’s carbonfibre tub called Monocage III. Aluminium subframes are attached front and rear, onto which mounts double-wishbone suspension at both ends.
The Senna’s engine, meanwhile, is an evolution of McLaren’s Ricardo-constructed 4.0-litre twin-turbocharged V8, dubbed M840TR. It produces 789bhp at 7250rpm and 590lb ft of torque between 5500rpm and 6700rpm; 79bhp and 22lb ft improvements on the closely related motor in the 720S. New induction manifolds, bespoke camshafts, high-flow fuel pumps and a new exhaust (made out of titanium and Inconel) allow it to make the outputs, and its power flows downstream to the road via a seven-speed dual-clutch gearbox.
While McLaren quotes a “lightest possible dry weight” for the Senna of 1198kg, the less widely known homologated kerb weight for the car (running order, with 100% fuel) is 1314kg. Our test car weighed 1345kg fully fuelled, where a 720S weighed a like-for-like 1420kg.
The Senna’s as-weighed power-to-weight ratio (587bhp per tonne) is therefore well beyond that of a 720S (500bhp per tonne as tested), although it’s just behind that of the Bugatti Veyron Supersport we tested in 2011 (593bhp per tonne).