Porsche enthusiasts are known for their devotion to the brand’s air-cooled classics, particularly the iconic 911. However, achieving significant power increases without altering the car’s character has always been a challenge. Enter Vonnen, a company that has developed a hybrid system designed to seamlessly integrate with air-cooled 911s, offering substantial performance gains without compromising the driving experience.
The brainchild of Chuck Moreland and his team, the Shadow Drive is an electric motor that fits between the engine and transaxle, designed to be virtually undetectable. The system’s goal is to enhance power while maintaining the car’s original feel. As Moreland puts it, “Our goal with the system was to basically make it disappear.” This approach ensures that the driving experience remains authentic, with the added benefit of increased performance.
The Shadow Drive’s Impressive Power Boost
The Shadow Drive offers two stages of performance enhancement. The stage one kit adds 75 horsepower and 75 lb-ft of torquewhile the stage two kit doubles that with 150 hp and 150 lb-ft of torque. These figures are particularly impressive considering that a stock 964 Carrera produced around 250 hp from the factory. The power increase is achieved without the typical trade-offs associated with other performance modifications, such as turbos or hot-rodded flat-sixes.
Thoughtful Design and Integration
One of the most remarkable aspects of the Shadow Drive is its thoughtful design and integration. The electric motor fits within the car’s bellhousing, ensuring that all additional power is sent directly to the crankshaft with minimal lag or parasitic losses. Vonnen has also addressed concerns about battery weight by replacing the standard 20-gallon fuel tank with a combined battery and fuel unit that occupies the same space. This modification results in a net weight change of only 44 poundsroughly equivalent to a stuffed suitcase.
The battery itself is a mere one kilowatt-hourwhich means it recharges quickly using energy from the engine and brakes. The separation between the engine and transmission is just 22 millimetersensuring that the system remains compact and unobtrusive. The trunk area remains largely unchanged, with the new battery and fuel unit hidden beneath the stock carpeting.
Customizable Performance and Compatibility
The Shadow Drive comes with a specialized controller that allows drivers to customize the hybrid system’s behavior using a smartphone app. This feature is particularly useful for tailoring the car’s performance to different driving scenarios, whether on the street or the track. The system can also adjust power delivery by gear, sending less torque in first gear to protect the transaxle and CV joints, and ramping it up in higher gears.
Perhaps most impressively, the Shadow Drive is compatible with all 911s from 1974 onwards, as well as 912s and 914s. It works with carbureted or fuel-injected engines, naturally aspirated or turbocharged setups, making it a versatile option for a wide range of classic Porsches. The system is also reversible, ensuring that the car can be restored to its original condition if desired.
While the Shadow Drive offers a seamless and powerful upgrade, it comes at a cost. The stage one kit is priced at $54,000and the stage two kit at $69,000before installation. However, for enthusiasts seeking a smart way to enhance their air-cooled 911’s performance without compromising its character, the Shadow Drive represents a compelling solution. It combines the benefits of electrification with minimal drawbacks, aside from the price, and is likely to appease even the most discerning Porsche purists.
