The Greenest Track Car

I had a feeling the eBox would win our "greenest" track car trophy, but I didn’t realize it would be so reliable throughout the day, and so fast. Josh took me on a quick drag run (and this is after the car had been beat on all day) and I can attest firsthand that this electric Scion is quick! It pulled happily all the way to 90mph before Josh backed off, and all the while the car was totally quiet.

The AC Propulsion conversion, done to first generation Scion xBs, costs close to $50k. But the car has a range of 150 miles and the recharge time is quite short. AC Propulsion didn’t do anything special to prepare for the track event. Other than the electric conversion, this is a bone stock xB, including the suspension. It helps that Josh (a vehicle product engineer for AC Propulsion) is a very skilled driver–he normally pilots an M Coupe track car.

Between sessions Josh took the eBox back to his little tent, plugged the car in and ran the AC to bring the battery temps down. Then he’d go back out onto the track and flog the little car some more. It ran in all four sessions, then Josh charged it up once more, hopped in and drove home to Monrovia, which was about 130 miles away.

What did the other racers think? Everyone loved it, and Josh got a big cheer when he got up on the podium to accept his trophy (he also scored third place in Shop Junior Varsity).

So how exactly did it win the "greenest track car" trophy? Well, we had John Fabijanic from Cal Poly on hand to determine the winner, and I have his full methodology after the jump.

Scoring is a very high-level methodology based on vehicle weight, power and fuel. Vehicles are scored relative to a baseline track car, a production 2009 Dodge Viper (3450 lb. dry weight, 600hp 8.4L V10 gasoline). The scoring method attempts to consider the total life cycle cost (LCC) which encompasses the energy to extract and produce the basic materials, to produce the vehicle, consumed during operation and for disposal. True total LCC is a relatively new way of evaluating vehicles and as such is still very much under development.

The green scores are weighted heavily (30% vehicle weight, 20% material weight reduction) to the overall vehicle weight. For a track car the number of miles driven can vary from miniscule if the car is tailored to the track to the same as a daily driver. This scoring model does not attempt to score this distinction and considers the total mileage driven to be very small compared to a daily driver. The great majority of energy consumed and therefore greenhouse gas released occurs during the actual production of the vehicle and again for its disposal. Therefore a lighter vehicle, i.e. less material, will require less energy to produce. Additionally, a lighter car is desirable as it requires less power to accelerate and decelerate. It is assumed that all cars are production based and have a similar material content proportion. A ‘bonus’ score is available for those who reduce the weight or change the construction of a production vehicle significantly. The score is based on the CO2 or energy required to produce the material compared to the replaced material.

The next greatest driver in the greenness of a vehicle is the amount of power produced. Less power equals less fuel. The power component of the scoring is weighted 30% of the total score. Finally, except for extremely long haul vehicles, is the choice of fuel. The relative CO2 production is determined based on fuel choice and relative engine power and is weighted 10% of the total score. The choice of fuel will also drive the amount of fuel and weight of fuel carried for equivalent power and duration. This additional fuel weight is accounted for and weighted 10% of the total score. All electric vehicles have a slightly modified scoring system with a fixed CO2 value, weighted for power output, based on Argonne Laboratory GREET results and no fuel weight penalty is levied as the battery weight is constant and is accounted for in the overall vehicle weight.

All scores are "bigger number is better." The material weight reduction score was zero for each car at this competition.

So here’s how it scored compared to the E85-powered WCM Ultralite, our fastest "green" track car:

Weight

xBox: 5
E85-powered WCM Ultralite: 39

Material

xBox: -
E85-powered WCM Ultralite: -

Power

xBox: 60
E85-powered WCM Ultralite: 17

Displacement

xBox: -
E85-powered WCM Ultralite: -

CO2

xBox: 75
E85-powered WCM Ultralite: 17

Fuel Weight

xBox: 0
E85-powered WCM Ultralite: 15

Total

xBox: 140
E85-powered WCM Ultralite: 89