Porsche people are purists. Well, usually, but I’m not here to talk about crazy edge cases. Instead, I’m here to share something with you all that I believe is pretty impressive: A geniously engineered hybrid system for aircooled 911s that might actually appease the fickle crowd.
It features very few trade-offs, whereas hot-rodded flat-sixes, turbos, and the like tend to have many. It’s the brainchild of Chuck Moreland and his crew at Vonnen, who designed an electric motor that sandwiches between the engine and transaxle. They call it the Shadow Drive because the entire concept is to make it seem like the system isn’t there at all.
“Our goal with the system was to basically make it disappear,” Moreland told me. “We want the driving experience to be as if it didn’t change. And that sounds silly because, of course, we want it to be more powerful. But what we’ve achieved is a system that basically isn’t there. You don’t see it. It doesn’t change the driving experience. It just makes it more powerful. And it’s as if it were just a more powerful and torquey engine.”
How much more power are we talkin’? Well, an extra 75 horsepower and 75 lb-ft of torque on the stage one kit, or 150 hp and 150 lb-ft of torque with the stage two. That’s more than respectable, considering these cars are fairly lightweight; also, a 964 Carrera only made around 250 hp from the factory to start with.
But the sheer power isn’t what’s most extraordinary about the Vonnen Shadow Drive. It’s the thoughtfulness.
That starts with the packaging, as the bulk of the motor fits inside the car’s bellhousing. All the extra power is sent directly to the crankshaft as a result, with no lag or parasitic losses to speak of. And Vonnen knows that folks mainly worry about the battery’s heftiness, so it addressed that with a clever solution that involves installing a smaller fuel tank and making good use of the newfound extra space.
“It’s a 20-gallon fuel tank, and we’ve modified the fuel tank to create a combination energy unit, which is both battery and fuel,” Moreland explained. “It sits in the same envelope as the original fuel tank. We gave up a few gallons of fuel to make that happen, but you still got a 15-gallon tank and better economy. So we didn’t significantly harm the range of the vehicle, and the weight of the battery is pretty light.
“You open the trunk, if you’ve got the stock carpeting in it, you’d be hard-pressed to know that there was any change at all because it’s all covered. You peel the carpeting back, and you can see that the fuel tank is a combined battery and fuel tank unit, but again, it’s inside the envelope of the original tank.”
Plus, the battery is only one kilowatt-hour. That means it also recharges quickly using energy from the engine as well as the brakes.
Vonnen built a 1988 Porsche 911 with its Shadow Drive installed. The net weight change was 44 pounds, or roughly the equivalent of a stuffed suitcase. The shop exchanged the heavy 12-volt battery for a lightweight one; ditched the spare tire, jack, and compressor; and removed the car’s starter motor, as its hybrid system now cranks the engine. Power lept to 335 hp, all without disrupting the car’s drivability.
And because Vonnen’s kit includes a specialized controller, drivers can select different drive modes for different scenarios with a smartphone app. Whether you’re on the street or the track, you can customize how the hybrid system behaves. It can also deploy power differently by gear, which is great news for people who don’t want to explode their transaxle or CV joints. Vonnen does this by sending less torque in first gear to preserve the hardware and then ramping it up in higher gears.
All this is to say, you don’t have to make a laundry list of modifications for the Shadow Drive to work on your car. Maybe the best part about it is that it’s compatible with all 911s from 1974 and up, as well as 912s and 914s. It doesn’t matter if the engine is carbureted or fuel-injected, naturally aspirated or turbocharged—it simply bolts up. So you can make your car as mild or as wild as you want, and Vonnen’s hybrid system will only complement the rest of your setup.
It also gives you that much extra performance without impacting the vehicle’s emissions, which is super important in states like California.
You’ll spend a lot for that level of convenience and versatility. The Shadow Drive stage one costs $54,000, while the stage two costs $69,000 before installation. Nothing about modifying these cars is cheap, of course, and you’re paying for the seamless integration as well as the added performance. Plus, it’s all reversible, so you don’t have to chop up your classic P-car to make it fit.
I’m not here to sell you on this kit. I’ll tell you first hand that I could never afford one. But if you’re looking at smart ways to get more power out of an aircooled 911, there’s arguably no more complete solution than this. It has all the benefits of electrification with practically zero of the drawbacks—aside from price—and if a purist ever got behind the wheel of one, I doubt they’d ever know it was there.
That’s kind of the point.
Got a tip or question for the author? Contact them directly: [email protected]
Read the full article here