The result is the Vonnen Shadow Drive, a performance hybrid system that adds performance to any 911. To achieve that it squeezes an electric Motor Generator Unit between the flat-six engine and the gearbox, much like Porsche will eventually do with its 992. It replaces the flywheel, that electric motor also removing the need for the starter motor. It’s a tight fit, being around 25mm in depth, shifting the gearbox forward by the same amount - and requiring a 25mm shorter prop to the front if it’s fitted to a Carrera 4 or Turbo model.
The batteries powering it are placed under the boot floor, and while Vonnen is currently quiet about the capacity and chemistry, it’s enough for the motor generator unit to deliver a 148bhp and 150lb.ft boost to the car’s overall output depending on the driving mode selected. There’s additional cooling circuits for the motor generator unit and the inverter supplying it, independent of the internal combustion engine’s cooling as they all operate at different temperatures. The system’s weight is around 95kg, but net it’s around 77kg due to the removal of the flywheel and the starter motor.
The electronic control of the flat-six is completely unchanged, too, the Vonnen Shadow Drive’s control unit only reading CAN bus data regarding the throttle position, to allow it to add its electric boost when required. The PDK here gets a re-flash, to counter the slippage from the clutches would otherwise occur but otherwise the car doesn’t know the Vonnen Shadow Drive is there.
The system can be entirely off, with no electrical assistance at all, while the Street mode adds 90lb.ft of torgue when the accelerator is between 40-60%. Sport mode adds 80lb.ft between 65-95% throttle and an Overboost mode adds the full 150lb.ft at the same rate as in Sport mode.
The system is hugely flexible, too, Moreland says that it can conceivably be fitted to any 911, manual or PDK, standard or tuned, naturally aspirated or turbocharged right back to 1965, though earlier cars would need some additional microswitches and sensors to monitor inputs.
It’ll fit in the Boxster and Cayman, too. Along with the 991 PDK 3.4 Carrera it’s fitted in here, Vonnen is currently applying it to a GT3 for further development. The cost presently is $75,000, which is huge, but it’s pioneering tech, which adds big performance without having any detrimental effect on emissions. Here, in California, and, increasingly, worldwide, that’s hugely significant.
Driving Vonnen’s Porsche 911 hybrid
Forget hybrid tech for economy or brief electric-only urban motoring, the Vonnen Shadow Drive is for performance. There’s nothing inside to highlight it’s fitted - if you ignore the power inverter located under the rear window, Vonnen saying it could be positioned out of sight if customers prefer.