Vonnen’s Shadow Drive system adds an electric motor—and a whole lot of power—to the venerable sports car. Having finally fought my way out of the congestion choking the San Jose suburbs, I take the 2013 Porsche 911 Carrera climbing up Skyline Boulevard. The 911 is an ideal match for the hills of Northern California, a lovely mix of balance and power. But Bill Davis, riding shotgun, isn’t here to sell me on a six-year-old car. “Floor it,” he says. Once my foot’s all the way down, he taps the smartphone mounted on the dashboard to engage the Vonnen Shadow Drive system. He’s part of the team that added an electric motor to the Porsche’s powertrain, making it a hybrid. And not the kind that’s going to save the planet. Instantly, that motor kicks in, boosting the native engine’s horsepower and torque by roughly 50 percent and giving me an idea of how Popeye feels after gulping spinach. Instead of punching a gang of no-goodniks out of the frame, though, I’m tearing through the hills of Northern California. “Oooooohhhhhhhhh,” I say, before getting on the brake and heading into a corner. That oooooohhhhhhhhh is what Davis and his colleagues at Vonnen have spent the last three year...