The result is the Vonnen Shadow Drive, a high-performance hybrid system that adds performance to any 911. To achieve this, it squeezes an electric motor generating unit between the six-cylinder flatbed engine and gearbox, much like Porsche will do with its 992. It replaces the flywheel, that electric motor that also eliminates the need for the starter motor. Its a tight fit, with a depth of about 25mm, that makes the gearbox move forward to the same extent, and requires a shorter 25mm strut at the front if mounted on a Carrera 4 or Turbo model.

The batteries that power it are placed under the boot, and although Vonnen is currently silent about capacity and chemistry, it is enough for the engine-generator unit to deliver an increase of 148bhp and 150lb.ft to the total output of the car depending on the driving mode selected. There are additional cooling circuits for the engine generator set and the inverter that feeds it, independent of the internal combustion engine cooling, as they all operate at different temperatures. The weight of the system is about 95 kg, but the net weight is about 77 kg due to the removal of the flywheel and starter.

The electronic control of the flat-six also remains unchanged, the Vonnen Shadow Drive control unit only reads CAN bus data relative to the throttle position, allowing you to add your electric pulse when needed. The PDK here receives a new flash, to counteract clutch slippage that would otherwise occur, but otherwise the car does not know that the Vonnen Shadow Drive is there.

The system can be completely off, without power assistance, while the Street mode adds 90lb.ft of torque when the throttle is between 40-60%. The Sport mode adds 80lb.ft between 65-95% acceleration and the Overboost mode adds full 150lb.ft at the same speed as in the Sport mode.

The system is also enormously flexible, says Moreland, and it is conceivable that it can be installed on any 911, manual or PDK, standard or tuned, naturally aspirated or turbocharged since 1965, although previous cars would need some additional microswitches and sensors to monitor inputs.

It also fits in the Boxster and the Cayman Islands. Along with the 991 PDK 3.4 Carrera that is installed here, Vonnen is currently applying it to a GT3 for further development. The current cost is $75,000, which is huge, but it is a pioneering technology, which adds great performance without having any detrimental effect on emissions. Here in California, and increasingly around the world, thats very significant.

Driving the Vonnen hybrid Porsche 911

Forget about hybrid technology for economy or just electric short urban driving, the Vonnen Shadow Drive is for performance. Theres nothing inside that stands out that its installed – if you ignore the power inverter under the rear window, Vonnen says it could be out of sight if customers prefer.

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