The high-pitched electrical whir sounds futuristic, but the flat-six thrum is decidedly mechanical—and all Porsche 911. Both noises are emanating from a 2013 991-generation coupe that has been retrofitted with a gas-electric hybrid system, turning the conventional 911 paradigm on its head by introducing electrons to the iconic sports car’s internal-combustion party.
Chuck Moreland of Elephant Racing fame is the man behind the tech, and Vonnen, his Santa Clara, California–based startup, wants to shift how Porsche owners think about performance. Vonnen’s impetus comes from two antipodes of performance tuning: Moreland, whose 30 years in aftermarket Porsche suspension work has focused on analog concepts like geometry, damping, and spring rates; and VP of Engineering Bill Davis, an EV-driving tech guy who’s worked for the likes of Tesla and NASA.
Vonnen’s hybrid setup was first prototyped on a 996 Carrera 2 converted to use a Carrera 4 transaxle before two years of development evolved it into the current 991-based system. In its current form, the so-called Shadow Drive package adds 150 horsepower and 150 lb-ft of torque via a frunk-mounted 1.0-kWh lithium-ion battery and a 9,000-rpm motor/generator unit in place of the flywheel. While the system leaves the Porsche’s 3.4-liter powerplant and braking system untouched, a control unit monitors variables like throttle and brake position, adjusting the supplemental electric torque accordingly. Also critical to the system’s behavior are the temperatures of the electric-drive components, which are regulated by separate cooling circuits and two additional radiators. In all, the added equipment adds 170 pounds of mass, some of which incrementally shifts the 911’s famously rearward weight distribution forward.
It’s been a minute since I’ve driven a 991.1-era 911, the model which predated the 991.2 versions that received torquier, turbocharged powerplants. As such, I’m initially a bit surprised by the relatively modest 287 lb-ft of pull with the hybrid system disengaged. Climbing Southern California’s Azusa Canyon Road, a sort of mini-me to the epic Angeles Crest Highway, it takes some patience to reach the meaty portion of the torque curve. After a few familiarization corners, Bill Davis activates the system via a phone app (all Vonnen systems will be operated by its proprietary app, not hard switches in the cabin). The hybrid powertrain, which can operate in Street, Sport, or Overboost modes, immediately makes its presence known with the aforementioned high-pitched hum. Also immediate is the heightened urgency when dipping the throttle. The PDK-equipped test car sometimes feels mild at higher rpm in internal-combustion-only mode, but it positively comes alive when the electric motor kicks in, offering considerably greater flexibility. A graph of system output in Overboost mode reveals a fat addition to the torque curve starting at around 1,300 rpm, and a considerable 61 percent increase at 2,000 rpm. The torque continues to pile on heavy to 5,000 rpm, where it peaks. The car is notably punchier with the aid of electrons, offering a rush of acceleration that counters the comparatively sluggish feel of the off-the-shelf 991.
But electrification is also a cruel mistress. When we first start exploiting the hybrid gear, its boost lasts as long as a few corners, but subsides when system temperatures elevate. Davis notes that the drive parameters are still being fine tuned, and we pull over for a quick tweak of the system using a laptop before we’re off and running again. Street mode only taps into about 65 percent of the system’s max power but it allows the good times to last longer. Sport calibrates for more top-end power, while Overboost goes for the full monty but reaches the thermal limits much more quickly.
In my experience, Overboost lasts just a couple of corners and straightaways before the system dials back to cool down and catch its breath. With a visible look of buzzkill falling across my face, Davis acknowledges the obvious gratification/delay issue, pointing out that doubling electric power means that you’ll be able to access it for approximately a quarter of the time. “It’s similar to [F1’s] KERS system,” he explains, “it’s designed for intermittent use.” In other words, nobody rides for free, especially when you’re adding a minimum amount of additional weight to the already wispy 911. But he also mentions that the cooling system’s design is still being tweaked and the final product should have “greatly improved” cooling with a wider operational window and/or faster recovery. And so I continue the cat and mouse game of savoring bursts of sweet acceleration, followed by patient cooldown cycles waiting for the next boosted state of charge. Meanwhile, the 991 exhibits the familiar core traits we’ve long enjoye—balanced handling, accurate steering, an unflappable chassis—with just a faint whiff of added weight on the nose due to the added hardware.
Catching up with Moreland after my drive, I point out the proverbial elephant in the room: that the new 992 generation’s chassis has accommodations for a future hybrid system. Doesn’t that worry him? “We’re glad that Porsche is moving in that direction, because it’s basically a blessing from the fatherland, if you will,” he says. “Basically they’re saying, hey, this is the right way to go.” Fair enough. But I’m still not sold on the idea that owners of 991s and 981s (and later, 997s and 996s) will be eager to spend $75K to retrofit their aging sports cars with hybrid tech.
But then Moreland shifts the conversation into an unexpected direction: older, air-cooled 911s. “Arguably, the air-cooled cars are a better fit because the big play here for us is to keep the character of the car, the engaging driver experience, and enhancing it with modern power.” Davis adds that electric power would also aid the warm-up process, which is notoriously lengthy because of air-cooled engines’ requirements for large amounts of slow-to-heat oil. Interestingly, the more I consider this argument, the more it holds water, so to speak. “I was concerned about the traditionalists rejecting [the Shadow Drive system] when we started the program,” Moreland says. “We went for the 991 first for that reason, and now we’re going to [develop] it for air-cooled cars. My concerns were misplaced, and we’ve had very little pushback from traditionalists saying it doesn’t belong on an air-cooled car.”
Now there’s a seriously counterintuitively back-to-zero concept: Let the newfangled factory 911s get the full works-developed hybrid and keep the retrofits to the retro cars. It’s weird, it’s bold, and it’s all but certain to disturb ardent hardliners who epitomize the air-cooled effete. For that last reason alone, an aftermarket hybrid system might just be worth of the cost of entry.