Reader Response, Draft 3 (Final Draft)

The 2017 Porsche 919’s power unit (9R9) consists of a directly injected, turbocharged two-litre V4 internal combustion engine (ICE) producing just under 500 horsepower, and two different energy recovery systems (ERS) (Newsroom 2017). The front axle mounted ERS converts kinetic energy under braking, while the rear axle mounted ERS converts energy from exhaust gases. Recuperated energy is stored in a liquid-cooled lithium-ion battery, which powers an electric motor capable of outputting over 400 horsepower, giving the 919 a combined total of over 900 horsepower. The 919 is predominantly rear wheel drive via ICE, but momentarily transforms into an all-wheel drive under acceleration, with the electric motor providing instant torque to the front axle. According to Andreani (2024), the 9R9 is Porsche’s most efficient hybrid race car engine to date. Without hybrid systems, an upwards of 20% increase in fuel consumption will be observed. Adhering to the Le Mans Prototype 1 (LMP1) Class regulations, the 919 was purpose built for endurance racing. The efficiency of the 9R9 was key for Porsche to dominate the only double-pointed race in the WEC calendar, the coveted 24 Hour of Le Mans, and ultimately, the LMP1 manufacturer’s championship.

Porsche’s use of a turbocharged 2.0L V4 engine illustrates how engine downsizing in endurance racing doesn’t compromise performance, but rather allows for superior aerodynamic and hybrid systems integration, resulting in increased fuel efficiency, and thus, a highly competitive race car.

In the LMP1 class, there were strict regulations governed by the Fédération Internationale de l'Automobile (FIA), and teams had to adhere to a stringent set of rules, which included: fuel flow, energy deployment and overall energy expenditure restrictions, different energy classes, no engine displacement restrictions, and among several other regulations, only a maximum of two separate aerodynamic packages (Fédération Internationale de l'Automobile, 2017). These unique efficiency regulations provided Porsche’s engineers with a platform for innovation, where they introduced drive concepts which incorporated hybrid systems and highly efficient engine downsizing (Newsroom 2017). In the four years Porsche competed, they won half of all the races in the LMP1 class, outperforming the likes of Audi, Toyota, and Nissan. Notably, these three manufacturers had one thing in common: their cars were equipped with comparatively larger V6 or V8 engines (WEC, 2016). 

Generally, an engine with a higher displacement can produce more horsepower and torque, and thus, achieve a greater top speed, as it can burn more air and fuel than a smaller engine (CFCS, 2023). However, particularly in endurance racing, having raw power without consideration for fuel efficiency might not yield a competitive package. There are key aerodynamic, suspension, chassis, and regulatory shortcomings associated with larger engines. A larger engine would require larger air intakes or vents, increasing aerodynamic drag (Sawaguchi, 2020), thereby reducing top speed on straights, which is especially detrimental for a circuit like Le Mans, with its four long straights. Suspension and dampers would have to be stiffer to compensate for the increased weight, making the car less predictable on uneven surfaces or big curbs (Lambert, 2021). A larger engine will physically take up more space, forcing engineers to compromise the placement of key systems, like the hybrid, gearbox, and exhaust. Finally, a larger engine might not meet regulatory requirements for power output and fuel flow, without significant modifications to the hybrid system, as both systems are interconnected by regulations that dictate their limits (FIA, 2017).

Porsche took engine downsizing to the extreme with the 9R9, employing a V4 configuration more commonly found in motorcycles. Porsche opted for a turbocharged V4 ICE as it was stiffer, compact, and lighter (Andreani, 2024), and also wanted a particular ratio between cylinder bore diameter and combustion chamber volume, which ruled out a larger V6 engine (Butcher, 2023). To compensate for the smaller engine, engineers had to implement two highly efficient ERS systems. These systems significantly reduced fuel consumption, keeping the 919’s consumption within the fuel flow limit, while simultaneously providing nearly half of the total horsepower. Crucially, this allowed the 919 to benefit from a smaller engine and a more compact aerodynamic package, which reduced drag without sacrificing raw power. With all things considered, privateer LMP1 teams that competed with naturally aspirated engines were often at a disadvantage due to the almost obligatory nature of the technical regulations surrounding hybridisation. This meant that Porsche's extensive, and almost compensatory, use of hybrid technology made the 919 an extremely competitive package, even against factory teams like Audi and Toyota.

Adopting such an extreme engine downsizing approach demanded meticulous planning and significant compromises. If Porsche hadn't executed it to perfection, the consequences would have been disastrous. Running high boost pressures in a turbocharger for extended periods, particularly in endurance racing, places immense strain on the entire power unit (Real Road Racing, 2018). This significantly reduces reliability and heightens the risk of catastrophic failure. In the early iterations of the 919, the V4 ICE produced considerable vibrations due to lack of developmental maturity and refinement, resulting in undesirable handling characteristics of the car, which almost undermined the entire concept of a V4 configuration.  During the planning phase, special consideration was also given to the rear-axle mounted ERS, which required slight modifications to ensure the electric motor and turbocharger were mounted separately, preventing a failure of the ERS from disabling the entire car (Butcher, 2023). In their first year of competing in LMP1 (2014), Porsche won only one of the eight races on the calendar and finished last in the manufacturers' championship, trailing significantly behind rivals Toyota and Audi in points. This was largely due to reliability issues, particularly evident at Le Mans, where they finished an appalling thirty laps behind the winning Audi.

In conclusion, Porsche’s choice to go with a smaller engine, coupled with a highly efficient hybrid system, proved to be the winning formula. The innovative use of technology, achieved by leveraging the rules and regulations to their fullest advantage, solidified their legacy as the most successful manufacturer in LMP1 history. Their ability to go against the grain and utilise the smallest engine in prototype racing history not only showcased their engineering prowess, but also demonstrated a strategic approach to performance and efficiency. This combination of creativity and adherence to regulations allowed Porsche to outpace competitors.

References

(2016, August 9). How the Porsche 919 Hybrid LMP racecar works. Retrieved 2024, from https://www.torque.com.sg/features/how-the-porsche-919-hybrid-lmp-racecar-works/

(2017, March). Porsche Newsroom. Retrieved 2024, from chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://newsroom.porsche.com/dam/jcr:7c981d12-d361-4158-8c0b-4ba930696f40/Press-kit_LMP1_2017_English_Web.pdf.

Clarita, C. F. C. S. (2023, August 9). Debunking the myth: Is a bigger car engine always better?. Medium. https://medium.com/@cashcashcars.com/debunking-the-myth-is-a-bigger-car-engine-always-better-1723a0655dea

Fédération Internationale de l'Automobile. (2017). 2017 technical regulations for LMP1 prototype hybrid. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.mulsannescorner.com/2017LMP1.pdf

Season 2016 Results. Season 2016 results - FIA world endurance championship. (2016). https://www.fiawec.com/en/season/result/24

Sawaguchi, T. (2020, January). Reduction of Aerodynamically Undesirable Influences Due to Engine Cooling Flow in Road Vehicle. https://www.scirp.org/journal/paperinformation?paperid=97184

Lambert, A. (2021, December 27). The most common racing suspension issues and how to fix them. Penske Racing Shocks - Made in America. https://www.penskeshocks.com/blog/the-most-common-racing-suspension-issues-and-how-to-fix-them#:~:text=If%20a%20shock%20is%20too,your%20car%20feel%20less%20predictable.

Butcher, L. (2023, June 9). Porsche’s Le mans comeback: How it built winning 919 “from nothing.” Motor Sport Magazine. https://www.motorsportmagazine.com/articles/100-years-of-le-mans/porsches-le-mans-comeback-how-it-built-winning-919-from-nothing/

Engine Downsizing: The Good and the Bad. Real Road Racing. (2018, June 19). https://realroadracing.com/engine-downsizing-the-good-and-the-bad/