The Most Effective Power Add-on for Air-Cooled Porsche 911s Could Be This Integrated Hybrid System.

      Vonnen

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      Porsche enthusiasts are typically purists. Well, most of the time, but let's not delve into the exceptions. Instead, I want to share something truly remarkable: a brilliantly designed hybrid system for air-cooled 911s that could win over even the most critical fans.

      This system features minimal compromises, unlike heavily tuned flat-sixes, turbos, and similar setups that often come with many drawbacks. It's the creation of Chuck Moreland and his team at Vonnen, who invented an electric motor that fits between the engine and transaxle. They refer to it as the Shadow Drive, as the goal is to make it feel as if the system is non-existent.

      “Our objective with the system was to essentially make it invisible,” Moreland told me. “We aimed for the driving experience to feel unchanged. It might sound absurd since we obviously want it to be more powerful, but what we've created is a system that feels like it’s not there at all. You don’t notice it. It doesn’t alter the driving experience; it simply enhances power. It feels akin to having a more powerful and torque-rich engine.”

      So, how much additional power are we discussing? The stage one kit yields an extra 75 horsepower and 75 lb-ft of torque, while the stage two kit offers 150 hp and 150 lb-ft of torque. These figures are impressive, particularly considering the relatively lightweight of these cars; a 964 Carrera originally produced around 250 hp from the factory.

      The team at Vonnen enjoys playing a game of "spot the motor" with onlookers, and even those who are familiar with what to look for often take time to notice it.

      However, the sheer power isn’t the most remarkable aspect of the Vonnen Shadow Drive; it’s the careful design.

      It all starts with the packaging, as most of the motor is integrated into the vehicle’s bellhousing. Consequently, the additional power is transmitted directly to the crankshaft, eliminating lag or parasitic losses. Vonnen is aware that people often worry about the weight of the battery, so they provided a clever solution involving a smaller fuel tank to make optimal use of the extra space.

      “It’s a 20-gallon fuel tank, which we have modified to serve as a combination energy unit that incorporates both battery and fuel,” Moreland explained. “It occupies the same space as the original fuel tank. We sacrificed a few gallons of fuel to achieve this, but it still provides a 15-gallon capacity with better fuel economy. So, we didn’t drastically reduce the vehicle’s range, and the battery’s weight is relatively light.

      “If you open the trunk, and if the stock carpeting is still in place, you would hardly notice any alteration because it’s all concealed. If you peel back the carpeting, you’ll see that the fuel tank is a combined battery and fuel tank, and it fits within the original tank’s envelope.”

      Additionally, the battery only has a capacity of one kilowatt-hour, which allows it to recharge quickly using energy from the engine as well as regenerative braking.

      Moreland mentioned that the gap between the engine and transmission measures just 22 millimeters, or 7/8 of an inch.

      Vonnen has built a 1988 Porsche 911 with the Shadow Drive installed, resulting in a net weight increase of 44 pounds, roughly equivalent to a heavily packed suitcase. The shop replaced the heavy 12-volt battery with a lighter one, eliminated the spare tire, jack, and compressor, and removed the car’s starter motor because its hybrid system now starts the engine. The power output jumped to 335 hp without affecting the car’s drivability.

      Since Vonnen’s kit comes with a specialized controller, drivers can choose from various drive modes for different situations using a smartphone app. Whether driving on the street or the track, you can customize the hybrid system’s behavior, and it can adjust power delivery based on the gear, which is beneficial for those concerned about damaging their transaxle or CV joints. Vonnen achieves this by sending less torque in first gear to protect the hardware and increasing it in higher gears.

      In summary, there’s no extensive list of modifications necessary for the Shadow Drive to be compatible with your vehicle. One of the most appealing aspects is its compatibility with all 911 models from 1974 onward, as well as 912s and 914s. It doesn’t matter whether the engine is carbureted or fuel-injected, naturally aspirated, or turbocharged—it simply bolts on. This means you can make your car as mild or extreme as you desire, and Vonnen’s hybrid system will enhance your setup.

      Moreover, it delivers that extra performance without affecting the vehicle’s emissions, which is particularly crucial in states like California.

      You will, however, pay a premium