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Vonnen Shadow Drive Porsche 911 quick drive: Aftermarket hybrids could change how we modify cars

This six-year-old Porsche is one of the most exciting cars I've driven this year. Of course, having been modified with an aftermarket hybrid system, it's no mere Carrera.

Antuan Goodwin Reviews Editor / Cars
Antuan Goodwin gained his automotive knowledge the old fashioned way, by turning wrenches in a driveway and picking up speeding tickets. From drivetrain tech and electrification to car audio installs and cabin tech, if it's on wheels, Antuan is knowledgeable.
Expertise Reviewing cars and car technology since 2008 focusing on electrification, driver assistance and infotainment Credentials
  • North American Car, Truck and SUV of the Year (NACTOY) Awards Juror
Antuan Goodwin
7 min read

Who'd have thought that a six-year-old 911 Carrera would be one of the most interesting cars I've driven in 2019?

Antuan Goodwin/Roadshow

Automotive modification is gearing up for an evolution. I know, because I've already driven it.

Recently, I found myself behind the wheel of a 2013 equipped with Vonnen Performance's Shadow Drive aftermarket hybrid system. It totally blew my mind. 

From basic bolt-ons to more involved forced induction setups, the road to more power and acceleration is a well-established one. Over the next few years, I believe that hybridization will join that list -- or, at least, it should. Vonnen's system allows enthusiasts to match the sound and thrill of driving a gasoline vehicle with a bit of electric sweetening.

The hardware

The Vonnen Shadow Drive hardware is deceptively simple, consisting of three main components. There's the motor, the battery and the control unit. 

The VSD electric motor is a thin-profile unit that sandwiches between the gasoline engine and the transmission, replacing the stock flywheel and starter in the process. Mostly tucked into the transmission's bell-housing, the whole thing only adds about an inch to the powertrain's length once installed and is basically invisible to the untrained eye when peering into the engine bay.


The VSD motor is a flat, donut-style unit.

Antuan Goodwin/Roadshow

Its position before the transmission means that VSD benefits from the same multispeed torque multiplication that the combustion engine does. It works with manual or automatic transmissions and both rear- and all-wheel-drive applications. The demonstration Carrera was a rear-drive model equipped with Porsche's PDK dual-clutch transmission.

Supplying power is a 1-kilowatt-hour battery hidden beneath the Porsche's front trunk. The chemistry of this lithium-ion battery is different from your average hybrid or EV pack. It's designed for rapid recharge and discharge -- sort of blending the speed of a capacitor and the capacity of a battery -- and can basically dump its entire capacity through the VSD in under 30 seconds.

The pack and VSD motor have separate cooling loops and radiators of their own, preferring different optimal operating temperatures.


Sandwiched between the engine and the transmission bell, Vonnen's system only adds an inch to the powertrain.

Antuan Goodwin/Roadshow

The third and final piece of the puzzle is the Vonnen Control Unit, a combination DC-to-AC inverter and piggyback microcontroller. The VCU pulls vehicle data via the onboard diagnostics port -- parameters such as throttle position, vehicle speed and more -- and uses that to calculate how much electric assist the motor should dole out and when to regenerate energy during braking or coasting. This is a one-way data connection that is totally invisible to the host vehicle's engine control unit and requires no modification to the Carrera other than plugging in. 

The VSD hardware and associated cooling loops weigh about 210 pounds overall. When you factor in the removal of the stock flywheel and starter, however, and step down to a smaller 12-volt battery -- since VSD will be handling cranking duties -- the net weight gain is only 170 pounds. Vonnen also tells me that by placing the battery up front to counter the extra mass added to the rear engine, the 911's weight balance is preserved.


The 1-kWh battery is smaller, but faster than the average hybrid. It lives beneath the Porsche's front trunk.

Antuan Goodwin/Roadshow

The drive

The hardware is controlled by a Vonnen smartphone app that pairs with the VCU, giving you the choice of three modes: Stealth, Sport and Overboost. 

Stealth and Sport both add 150 horsepower and 100 pound-feet of torque to the Carrera's 350 hp and 287 lb-ft. However, the two modes differ in how they ration that power out. Stealth sticks mostly to the low-to-mid-rpm range, adding a bit of extra "oomph" to the street driving experience around town for better off-the-line performance. Sport comes in a bit stronger and more pronounced in the midrange; this is your track day and backroad blitz mode. 

One hundred extra pound-feet is definitely a significant upgrade. The whole car feels much more confident when merging on the highway and accelerating for a pass. True to its name, Shadow Drive is mostly transparent in its operation; if you didn't tell me that there was a hybrid system behind the scenes, I probably wouldn't know. It still sounds like a flat-six -- albeit with a very slight electronic whine from the motor and inverter coils, which was mounted on the rear parcel shelf on the demo car -- and still delivers flat-six fuel fuel economy, which I'll get back to in a minute.

Vonnen Shadow Drive

The hybrid system is compatible with automatic and manual transmissions, rear or all-wheel drive.

Vonnen Performance

The third mode is Overboost, a setting that boosts torque output to 150 pound-feet and kicks the electric assist to full-steam. This mode really heats up the VSD 911's performance, piling on the power for a quite quick 0-to-60-mph sprint of about 3.6 seconds, an improvement over the stock Carrera's 5.0-second time. Along the way, the system's slight coil whine becomes more pronounced, sounding more like a swarm of angry electric bees and contributing to the feeling that this has become a very different car with just the touch of a button.

Overboost mode also literally heats up the VSD system, however, pushing the limits of its thermal management system. After a few full-tilt sprints, the hardware is heat-soaked and must limit power until it cools down again, limiting Overboost to brief demonstrations of VSD's potential. Vonnen recommends using Stealth or Sport for more consistent performance during street and track driving and I found them to still be quite impressive up and down my favorite Santa Cruz mountain hill climb.

Technically, there is a fourth mode -- Off -- which serves as a valet mode and also allowed me to get a baseline of the 911's performance sans electric assist. 

The implications

The VSD electric motor never turns the wheels on its own; this is purely an assist system, the mildest of hybrids . Vonnen tells me that there is no direct benefit or gain to fuel economy. There are indirect benefits to consider, however. 


The Vonnen Control Unit pulls vehicle data via the diagnostics port and manages electric assist and regen.

Antuan Goodwin/Roadshow

For starters, though there isn't a gain, there also isn't a loss in economy. Unlike adding a similarly powerful turbocharger or supercharger, Vonnen claims that Shadow Drive uses no more fuel than stock -- around town or during spirited driving -- with almost no parasitic drag and no need for larger injectors. VSD's performance is self-contained and comes completely from recaptured waste energy.

Because Vonnen's system is invisible to emissions software and makes no changes to emissions hardware, it should also be completely CARB and smog inspection legal.

And, in a world where increasingly stringent emissions software is reducing the effectiveness of traditional bolt-ons -- your intake, exhaust, header upgrade path -- sidestepping these systems with hybridization is a compelling alternative. Hybrid systems, like Vonnen Shadow Drive, are also easier to adapt to different vehicles. Being largely self-contained, any car that has an inch of wiggle room in its powertrain and a place to mount the battery, VCU and cooling radiators is already mostly compatible. Brackets and a bit of over-the-air updatable software tuning are, in theory, the only changes needed to go from a 2013 991 to an air-cooled 964… in theory.


Adding about 100 pound-feet of torque makes the Carrera's flat-six feel like a flat-eight.

Vonnen Performance

Then again, Shadow Drive is also compatible with modified vehicles, so if you've got an aftermarket exhaust that you just love the sound of, it'll work and sound just as good with VSD. The same goes for conventional forced induction systems and other engine modifications, if you want a beastly turbocharged hybrid with customs cams, water injection or whatever, it should all work with Vonnen's system.

The price

There is one really big "but," and that is the price. Right now, the Vonnen Shadow Drive system costs around $75,000 installed. You give Vonnen seventy-five thousand bucks and your 991-series Porsche 911 (2012-2019) or 981-series or Cayman , and after a little bit of time Vonnen will give you your car back with the hybrid system and an extra 150 pound-feet of torque. (Older generation Boxsters and Caymans, as well as 997, 996 and air-cooled 911s are also soon to be supported or in development.)

That means Vonnen's Shadow Drive alone costs as much as the 2013 Carrera upon which it is installed. Of course, that vehicle was chosen for development and demonstration purposes and one of the benefits of the VSD is that it's compatible with the entire series -- from Carreras to Targas, Turbos and GT3s. For more expensive, big-ticket models, the benefit of nondestructive modification may make the VSD's sticker price less shocking. The cost-to-benefit ratio could be even better as development opens applications for rare, air-cooled Porsches, allowing collectors to enjoy these cars without ruining their investment.


It's a bit pricey and still early days, but Vonnen's hybrid technology presents some exciting implications for the future of tuning and modification.

Vonnen Performance

VSD is still less expensive, less complicated and less destructive to the host vehicle than a full electric conversion. And eventually, economic scaling will bring the price down. Further experimentation with smaller batteries -- the most expensive part of the package -- or motors for lighter applications could further improve affordability. Vonnen's reps told me it is also looking at vehicles beyond Porsche, but I couldn't get anyone to specify what applications are in the pipeline. It'll maybe never get to the point where it makes financial sense to slap a VSD on my Miata, but one can dream.

I left Vonnen Performance's Santa Clara office with my head reeling at the implications and potential that aftermarket hybridization has to offer enthusiasts and modifiers. VSD isn't here to replace the modifications you know and love; it's not here to dumb down performance driving; it's not even here to save the environment. Electrification is another tool in the pursuit of speed, a tool with tremendous potential even in these early adopter days and -- I think -- one of the most exciting things happening in the modern aftermarket space.