The year 2025 marks the final Formula 1 season for power units introduced with the 2014 regulations. Despite a long 12-season period, including only 9 years of unrestricted development before the freeze in 2022, the technical cycle concludes without absolute convergence, with two equally valid philosophies. Until the end, Ferrari has remained the sole staunch supporter of the compact turbocharger engine, resisting the split turbo embraced by Mercedes, Honda, and Renault. However, this choice has left no regrets.
The split turbo
Mercedes was the first manufacturer to introduce the split turbo architecture for hybrid power units. This solution separates the turbine, powered by hot exhaust gases, from the compressor, which compresses the air entering the engine. A rotating shaft connects the two components, with the MGU-H positioned in between. The MGU-H is an electric motor driven by the turbine to recharge energy, but it can also perform work to accelerate the compressor.
Honda followed Mercedes, introducing a split turbo architecture, which Renault later adopted with its 2022 power unit. That same year, it was speculated that Ferrari might also adopt this design, but the Maranello technicians and engineers chose to continue with its philosophy. “In our architecture, the MGU-H is mounted in front of the turbocharger,” explained Enrico Gualtieri, head of Ferrari’s engine department, in 2023. “Over the years, we decided to maintain this solution, which is unusual compared to our competitors. The choice was to keep a compact turbo-MGU-H assembly rather than separating them, allowing the entire unit to fit within the V of the engine between the two cylinder banks.”
The advantages
In a 2021 interview with the Ialian media, then Honda F1 technical director Toyoharu Tanabe discussed the decision to adopt the split turbo: “We gained experience with the compact solution before moving to the configuration with separated turbine and compressor, as we at Honda benefit from this setup. We learned a lot from both the previous and the current designs. Perhaps there are advantages to the compact turbocharger, but since we never went back to that solution, I can’t say for certain. However, the current architecture is one of the best compromises.”
The preference for one concept over another depends on the aspects chosen to be prioritized, aiming for the best possible compromise between weight, size, and engine performance. The split turbo, for example, separates the turbine and compressor, placing them outside the engine block. This arrangement allows the connecting shaft and the MGU-H to be housed between the two cylinder banks, lowering the entire turbocharger assembly.
On one hand, the split turbo helps lower the center of gravity while ensuring compact dimensions and greater freedom for the aerodynamics department in designing the car’s bodywork. However, the equation also includes the shapes of the intake and exhaust ducts, the air and gas pressure losses within them, the usable engine power, and the electrical energy that can be regenerated through the MGU-H. “From the perspective of power unit performance, we need a certain level of power obtained through energy regeneration,” Tanabe explained in 2021. “The split turbo package could also impact aerodynamics, but overall, the advantages in terms of power unit competitiveness are greater, which is why we chose this solution.”
Ferrari’s philosophy
Over the years, Maranello’s engine department has repeatedly explored the split turbo architecture but never found the same advantages as its rivals, continuing instead with its own path. This is also due to different choices regarding the compressor, with Ferrari opting for a smaller compressor compared to competitors, prioritizing lower weight, ease of achieving high rotational speeds, and better response at low revs. The compact size allowed—and still allows—Ferrari to fit the turbocharger assembly within the space between the cylinder banks, offering similar benefits to the split turbo, at least in terms of size and aerodynamics.
The duality between the two philosophies is, however, set to end in the 2026 Formula 1 championship. The upcoming regulations, besides removing the MGU-H, impose maximum and minimum diameters for the turbine and compressor and, most importantly, limit the distance between the two components to 175 mm. The split turbo is set to disappear from Formula 1 after captivating all manufacturers from 2014 to today, though it never managed to convince Ferrari.
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