On our show, we like extreme tech. And, as far as we're concerned, racing go-karts at 90 mph with your butt half an inch off the ground certainly qualifies as extreme. With scary acceleration and speed, high-performance karts are as exhilarating as it gets in racing circles. But these track-only rides use two-stroke engines, which are notoriously dirty--one kart can spew as many pollutants as 100 cars.

We care about the environment and want to do our part, but still have a little fun. So we wondered: Could we create an electric kart that would outperform its noisy, gas-powered twin--and be just as thrilling?

Starting with two Tony Kart gas models, we converted one to electric in 12 hours flat. (We even amazed ourselves.) We used a 25-hp brushed DC (direct current) electric motor and an industrial controller from a golf cart, and then focused on four details that can trip up electric vehicles--torque curves, weight, batteries and cost. Cameras in tow, we headed out to Infineon Raceway in Sonoma, Calif. Race tracks, loud noises and burning rubber: just an average day on a MythBusters shoot.

Cruise Control

Photograph by Mark Richards

Adam: I had to create a link between the throttle pedal and the potentiometer, which is a mechanical device that tells the speed controller how much pressure is on the throttle pedal. The speed controller translates that signal to regulate how much amperage is sent to the motor--and that determines how fast the kart will go. Here, we're testing the linkage.

Battery 101

Photograph by Mark Richard

Jamie: Most manufacturers plan on using lithium-ion batteries in future hybrids and electric cars, but some current types can suffer from thermal runaway, or overheating, and catch fire. We avoided this by using lithium-iron-phosphate batteries from Thunder-Sky. They aren't as sensitive to temperature, but they do need to be kept under pressure. This bracket is part of a vice I'm building for the batteries. As they heat up, they can swell and crack the casing if they're not squeezed together. We used 28 batteries with a total of 110 volts. The kart can be charged to 80 percent in an hour and 100 percent overnight.

Slot Machine

Photograph by Mark Richard

Adam: I'm using an oxyacetylene torch to cut a motor mount, which has slots--not holes--so that the tension the motor puts on whatever it's driving can be adjusted. You learn this the very first time you don't do it and wreck a motor. Everyone I know has ruined a motor this way.

The Need for Speed

Photograph by Mark Richard

Adam: As soon as our kart was charged, we went out to the track in Sonoma, Calif., and got ready to race. I'd never driven a go-kart. I had a ton of spinouts learning how it's done, but it was a good opportunity to smoke the tires. (Until they get warmed up and kind of soft, you don't have any traction.) The roar of the gas motor is something that's carnally interesting--like the first time I rode a motorcycle--so the absence of that noise in the electric was disconcerting, but it was easily outweighed by how fast the kart got off the line. Jamie: Our electric flattened your ears coming out of a curve. But once the gas kart hit its butter zone at 15,000 rpm, it was almost too hot to handle.

Photo Finish

Photograph by Mark Richards

"My lap time for both karts was under a minute, but the track record was 13 seconds faster," says rookie racer Savage, shown here conferring with the beret-wearing Hyneman. "It's like watching Tiger Woods play golf--I have no idea how you'd shave 13 seconds off what I was doing."

Jamie: In the end, the karts' lap times were within 1 second of each other, even though the electric was significantly heavier. The electric's off-the-line acceleration was much higher than the gas's, but the top-end acceleration of the gas kart was greater than that of the electric, so it balanced out.

Adam: If we'd had more than a day on the build, we would have goosed the electric's perform­ance by adjusting the linkage between the throttle and potentiometer.

Bottom Line

Photograph by Mark Richard

Adam: So what did our tests tell us? Electric vehicles are here to stay. Although the electric kart weighed almost twice as much as the gas version, it performed about as well. That means there's a lot of power in those batteries and a lot of potential in electric vehicles. Jamie: With electrics, you generate a fraction of the pollution per mile that you do with gas vehicles--without any sacrifice to those of us in a hurry.

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