The "added lightness" mantra is well-known in performance circles--cutting weight helps everything about a sports car, from acceleration to braking to handling. And it also helps out emissions, it turns out. Lotus today announced the 2011 Elise scored 46.6 mpg US and a mere 239 grams of CO2 emissions per mile, making it the cleanest, most efficient gasoline-powered car in its performance category.

We brought you news of the 2011 Lotus Elise's switch to a new 1.6-liter four-cylinder engine when the car was unveiled in February. At the time, Lotus estimated the fuel economy and emissions improvements to be around 23 percent and 13 percent respectively, figures that have proved accurate. Gains were also made thanks to improvements in aerodynamics, which cut drag by four percent.

The 136-horsepower mill might not sound like a barnstormer, but in the new Elise's 1,934-pound package, it's enough to get the car to 60 mph in 6.0 seconds. The combination of efficiency and performance--albeit in a highly focused, not-particularly-utilitarian package--belies the greenlings' prejudice against dino juice in general and gasoline in particular.

For comparison, the 2010 Toyota Prius, which takes just under 10 seconds to reach 60 mph, manages a slightly better 50 mpg combined rating from the EPA, and emits 148 grams of CO2 per mile. But it requires a much more complex hybrid system to do so, thought it also has a back seat.

Perhaps even more illustrative is the 2011 Honda CR-Z's spec sheet. Powered by a 1.5-liter engine and Honda's IMA hybrid system, the CR-Z two-seat hatchback manages just 31/37 mpg city/highway with the manual transmission, for a combined rating likely to fall in the mid-30s--and like the Prius, it's expected to take about 10 seconds to reach 60 mph. Emissions are estimated at about 188 grams per mile. Both the Prius and the CR-Z score better in emissions testing than the Lotus due to start-stop technology enabled by their hybrid systems.

Even if the 2011 Lotus Elise isn't the greenest car on the planet, it certainly proves that you don't have to give up fun to go green.