Ferrari Stradale transfers recent advances of Scuderia Ferrari competition cars to the road. To better understand Stradale, we turned to Ferrari’s Chief Technology Officer, Michael Leiters, who was joined by Vittorio Dini, Head of Powertrain, and Matteo Biancalana, Ferrari’s aerodynamics chief.
How has the technology of Scuderia Ferrari informed Stradale?
“Ferrari road cars have always been the embodiment of the transfer of racing technology,” says Ferrari Chief Technology Officer Michael Leiters. “Our top engineers from Formula 1 and our road car department meet regularly to discuss technology developments, be it know-how, methodology, software or materials.”
“Formula1 moved to hybrid architecture in 2014 in order to achieve higher levels of performance combined with a higher overall efficiency,” says Leiters. “The quest for higher performance is what pushed the team to move towards a hybrid architecture on road cars. The SF90 Stradale incorporates a number of areas of development that are inspired by Ferrari’s F1 cars, including the extreme interpretation of Ferrari’s ethos of HMI [Human Machine Interface], with the driver’s hands always on the steering wheel.”
Controls for headlights, windscreen wipers, indicators and the Manettino for driving modes all reside on the steering wheel. New HMI controls include the compact pad on the right-hand spoke that allows the driver to navigate the central screen, while voice and cruise controls are on the left-hand spoke. Also, a rotary switch for cruise control is a solution derived directly from the Formula 1 car. In the bottom left section of the central area, there are four buttons the driver uses to select the mode of the power unit: eDrive, which powers the car solely with the electric front axle; Hybrid, which is a default setting that can turn the gasoline engine off and on; Performance, which keeps the gasoline engine engaged at all times; and Qualify, a pure performance setting that allows the electric motors to work at full potential without any demands for recharging the batteries. Stradale also hearkens to the past, with F1 controls on the “bridge” completely redesigned and set into a modern metal plate that echoes a Ferrari design signature of the past: the classic gear lever gate.
“Also, there is a form of DRS [Drag Reduction System] at the rear with the shut-off Gurney,” adds Matteo Biancalana, who is Ferrari’s Master of the Windtunnel, the head of the aerodynamics department. Ferrari’s elaboration of the “Gurney Flap” is a patented active system located at the rear of the car that regulates air flow over the upper body, reducing drag at high speeds in a straight or gentle arc, and increasing downforce when cornering, under braking and during changes of direction.
Also derived from Formula 1 is the “know-how that goes into the design of the combustion chamber and the MGUK [Motor Generator Unit, Kinetic], which is the rear electric motor connected to the thermal engine,” says Vittorio Dini, Head of Powertrain. “The SF90 Stradale’s MGUK and the brake-by-wire system, which is necessary to control the brakes and to allow energy recovery front and rear without compromising brake feeling and performance, were designed using experience coming from the track.”
“The challenges are how we go about the integration of the electric motors to limit the increase in weight,” says Dini. “The advantage comes from being able to control the electric motor better than a mechanical set-up. In addition, the component is modular and, in this application, we have named the system RAC-e – Regolatore Angolo di Curva Elettrico (electronic cornering angle regulation) thanks to its torque vectoring characteristics.” RAC-e is the “electric” front axle, left- and right-side electric motors. Combined with Electronic Traction Control on all four wheels, it is possible to exploit with extreme precision the additional grip of the front wheels. Improved overall grip combined with improved power delivery from the electric motors at low speeds allows SF90 Stradale to set new benchmarks for standing-start acceleration. The car runs from 0-100 kph (0-62 mph) in 2.5 seconds, yet it is by no means a one-dimensional acceleration sled. It is a Ferrari and thus has exquisite cornering capability, too.
Electric motor torque fill allowed you to move the gas engine’s torque peak far up the rev range? Is this how you gained the additional gasoline power?
“No, you’re thinking about the LaFerrari! The V8 powering the SF90 Stradale is a development of the family of engines (F154) that has taken the overall International Engine of the Year award now for the fourth year running,” says Dini, “a feat that no other car manufacturer has ever achieved. The increase in power was achieved first and foremost by the new cylinder head with new fluid dynamics and combustion chamber. The new combustion chamber features a central injector and 350-bar direct-injection pressure to improve the mixture and combustion stability. The design of the combustion chamber benefits from the increase in bore of 1mm, which allowed more space for the valves.”
“To improve the internal fluid dynamics, not only was a larger diameter intake valve adopted, but the ducts are all horizontally lined up at engine head height,” says Dini. “The turbocharger assembly has been improved with new compressor and turbine housings with reduced back-pressure. The turbos are equipped with electronically controlled wastegates to improve catalyst heating and new compressor volutes to optimize fluid-dynamics. The new combustion chamber improves the combustion stability and reduces knocking (pinging) therefore improving emissions at low loads as well as performance in wide-open throttle,” says Dini. A slightly wider and larger combustion chamber allows bigger intake valves that flow more air boosted by more efficient, smoother turbochargers, all fired off with an ultra-precise and high-pressure shot of fuel. And the engine is very clean at low revs yet also with the throttle mashed wide open. A virtuous circle, so to speak.
Does the rear electric motor impact the revvy nature of the gasoline engine?
“No. The rear electric motor has a transient response that is even faster than that of a combustion engine,” says Dini, “and can therefore offset the moment of inertia of the rotor.” The electric motor reacts to throttle input faster than the gasoline engine, so there is no impact on the character of a Ferrari engine.
How did you retain Ferrari characteristics of musicality and revviness and playfulness?
“Musicality: we always apply the same design criteria for the exhaust manifold (equal-length exhaust runners) and tuning and we have maintained the thin-wall Inconel exhaust manifolds like in the 488 Pista and F8 Tributo,” says Dini. “Revviness and playfulness: all our engines are well known for their revvy nature and we always apply the same control strategies which we develop in-house and which we improve from model to model.”
Can you describe the gearbox? This is a variant of the Tributo gearbox?
“Yes, it shifts a milli-second quicker,” says Leiters. “How? The gearbox is an all-new 8-speed design with all-new ratios and a more compact clutch assembly, contributing to a 15mm reduction of the installed height in the car for a lower center of gravity. The weight of the 8-speed is also 7kg [15.4 lbs.] lighter than the current 7-speed gearbox. Reverse gear has also been removed, as this function is carried out by the front electric motors. New-generation actuation hydraulics reduce total clutch fill times to 200ms compared to the 488 Pista’s 300ms.” The new gearbox has 8-speeds, is smaller in size and significantly lighter, sits lower in the car, and shift speeds are approaching purely synaptic.
Stradale is about 500 pounds heavier than Tributo. Is that all from the battery pack and electric motors?
“Obviously the batteries, three motors and cabling are included in the 240kg dry weight difference between the two cars,” says Dini. But Ferrari kept weight at 1570kg (3461 lbs.). Using American measures for horsepower, which put Stradale at 986 horsepower, the car has a power-to-weight ratio of 3.5 pounds per horsepower, which is extraordinary. Stradale is about 1000 pounds lighter than a Bugatti Chiron, which has similar straight-line acceleration, but due to its considerable weight and also bias to ultra-high top speed, Chiron has a very narrow focus and cannot approach the handling prowess and thus real-world performance of Stradale. Stradale is a decathlete that can run as quickly as the world's best sprinter.
What steps did you take in structure and elsewhere to compensate for the added weight and complexity?
“The entire chassis/body-in-white is new,” says Leiters. “We engineer our chassis with a multi-material, multi-technology approach to optimize weight and performance. In other words, we chose the best kind of material and the correct technology depending on the area of application. A good example is the use of carbon-fiber for the rear firewall, the front bonnet and front and rear bumpers. The body-in-white employs seven different kinds of aluminium alloy and four different manufacturing technologies, with the result that it is both lighter and stiffer than previous mid-rear V8 chassis.”
Does Stradale have an S-duct like 488 Pista and the new Tributo?
“No,” says Biancalana. “However, the SF90 Stradale is the new benchmark for downforce and efficiency in high-performance road cars, with 390 kg [860 lbs.] of downforce at 250 km/h [155 mph].”
Stradale Ferrari practice, controlling air flow over and under, along the sides and through the bodywork? Does Stradale introduce new aero tricks?
“To reduce turbulence along the car’s flanks,” says Biancalana, “the hot air flow coming off the front-mounted coolant radiators is channeled principally to the front underbody and the vents on the front bumper just ahead of the front wheels, while only a minimal percentage of air is evacuated into the front wheelarch. This lowers pressure in the wheelarches themselves, thereby also reducing the amount of turbulence along the sides and virtually fairing both the exposed section of the front wheels below the aerodynamic underbody and the outer section. This solution has the further advantage of preventing the hot air coming off the front-mounted radiators negatively impacting the intercoolers. The front bumper also has a convex section in planview which benefits front downforce. That said, most of the front downforce is actually generated by the underbody, which has been raised by 15mm and features eight pairs of vortex generators that protrude into the front wheelarch.”
“The most innovative downforce management device on the car is the shut-off Gurney on the end section of the engine cover,” says Biancalana. “It consists of a suspended wing divided into two sections. One fixed and one mobile. In conditions of low down-force the two sections are aligned, allowing the air to flow above and below the shut-off Gurney. In high downforce conditions (cornering, braking or abrupt changes of direction) , the mobile element is lowered by a pair of electric actuators, closing the lower blown area and uncovering the fixed element, generating a new tail geometry characterized by a broad load surface topped by a powerful nolder,” says Biancalana.
The coming decade of Ferrari berlinettas is heralded by Stradale. To see all these features in compelling videos, Ferrari has a dedicated website for Stradale.
