Sports car buyers and fuel economy-minded car buyers are generally not the same people, but it's no secret that there are plenty of cars on the market that deliver lots of power and reasonable fuel economy at the same time. We decided not to focus on the typical targets, many of whom return 30 mpg thanks to four-cylinder engines and compact footprints, and look at the big, muscular stuff. The following list is the top 10 greenest sports cars (coupes and convertibles, specifically) with more than 400 horsepower underhood.
First Place: 2013 Mercedes-Benz SLK55 AMG: 415 hp / 398 lb-ft, 19 mpg city, 28 mpg highway
There are a few Mercedes-Benzes on this list, and for good reason: Mercedes-Benz is on a roll with downsizing its V-8 engines and adding turbochargers, which usually adds a small amount of power and a large amount of fuel economy. Surprisingly, the SLK55 AMG is not one of those cars: it's powered by a 5.5-liter V-8 engine without turbos. Still, it benefits from one thing: it's a small car with a big engine, so it doesn't take much power to keep the SLK55 at speed. Additional help comes from technologies like engine stop-start and cylinder deactivation.
Second Place: 2013 Porsche 911 Carrera S: 400 hp / 325 lb-ft, 19-20 mpg city, 27 mpg highway
Logic would suggest that a car with six cylinders will use less gas than one with eight. While that's not always true, that logic does apply to our second-place entry, the Porsche 911 Carrera S. The 911 Carrera S has 400 horsepower on tap, the lowest of any of the list entries, but it's no slouch, either. The speed and economy are both aided by Porsche's seven-speed transmissions--one manual, one dual-clutch auto--and the 911 Carrera's signature, aerodynamic shape.
Third Place: 2013 Mercedes-Benz E550 Coupe: 402 hp / 443 lb-ft, 17 mpg city, 27 mpg highway
The E550 coupe is one of many Mercedes-Benzes to follow the brand's recent engine downsizing trend. While past E550s featured 5.5-liter normally-aspirated V-8 engines, this one has a 4.6-liter twin-turbo V-8 under the hood, mated to a seven-speed automatic transmission. Thanks in part to the smaller engine and in part to the taller top gear, the E550 returns a respectable 21 mpg combined.
Fourth Place: 2013 Ford Mustang GT Coupe: 420 hp / 390 lb-ft, 15-18 mpg city, 25-26 mpg highway
Yes, the Ford Mustang is aging, but it's powered by a relatively new 5.0-liter V-8 engine (aptly named Coyote) that far surpasses its predecessor in both power and economy. It ties or beats the usual champion of American muscle car fuel economy, the Chevrolet Corvette, thanks in part to an available six-speed automatic that boosts city fuel economy. True gearheads will stick for the manual, however, losing just one mpg combined in the process.
Fifth Place: BMW 650i Coupe: 400 hp / 450 lb-ft, 17 mpg city, 25 mpg highway
Like Mercedes-Benz, BMW has been hard at work downsizing and turbocharging its engines for greater power and economy. The 650i coupe is not powered by a 5.0-liter V-8 as its name would suggest, but rather a 4.4-liter twin-turbo V-8 (the same engine that does duty in many other BMWs, including the M5 and M6, albeit in a different state of tune). What it lacks in raucous engine noise it makes up for in fuel economy.
Sixth Place: Chevrolet Corvette: 430 hp / 424 lb-ft, 15-16 mpg city, 25-26 mpg highway
The Corvette has long been the champion of American muscle car fuel economy for one reason: it's very light. Car fans willing to put up with the Corvette's notoriously plasticky interior are rewarded not only with 430 hp but also a 19 mpg combined rating from the EPA. Buyers who want more horsepower can opt for the Corvette Z06, whose 7.0-liter V-8 engine churns out 505 horsepower and returns 15 mpg city / 24 mpg highway, about the same as our tenth place entry.
Seventh Place: Mercedes-Benz SL63 AMG: 530 hp / 590 lb-ft (557 hp / 664 lb-ft with performance package), 16 mpg city, 25 mpg highway
Unlike the SLK55 AMG, the SL63 is one of Mercedes-Benz's AMG models featuring engine downsizing. The engineers at AMG threw out the SL63's old 6.2-liter V-8 and replaced it with a twin-turbo 5.5-liter V-8 and a seven-speed automatic transmission, which boosted both power and economy. Credit also goes to the SL's ultra-lightweight aluminum structure. For leadfoots with lots of money to blow, Mercedes-Benz offers a performance package for the SL63, which ups the turbocharged engine's power output to an impressive 557 hp and a ridiculous 664 lb-ft of torque, without changing the overall fuel economy.
Eighth Place: Chevrolet Camaro SS: 426 hp / 420 lb-ft (400 hp / 410 lb-ft with automatic transmission), 16-17 mpg city, 24-28 mpg highway
If the relatively light Corvette scores points with its 6.2-liter V-8, how does the heavier Camaro SS fare with (roughly) the same engine? Pretty well: it scores up to 28 mpg on the highway. Granted, that rating is with the automatic transmission; a Camaro fan in the know will opt for the manual transmission, which allows the engine to make more power, and will force the driver to shift from first to fourth gear under light throttle in the interest of saving gas.
Ninth Place: Nissan GT-R: 545 hp / 463 lb-ft, 16 mpg city, 23 mpg highway
The Porsche 911 scores points on this list for having a 3.8-liter six-cylinder engine, but the Nissan GT-R earns its place on this list by taking a 3.8-liter V-6 and adding two large turbochargers. The result is a neck-snapping 545 hp, but a 23 mpg highway when you take the car out of "R" sport mode and drive gingerly.
Tenth Place: Audi RS5: 450 hp / 320 lb-ft, 16 mpg city, 23 mpg highway
The Audi RS5's engine doesn't use many fancy tricks to score its fuel economy numbers--it's the same 4.2-liter V-8, albeit in a different state of tune, as the old RS4. Still, the RS5 is one of the first Audis to receive the new corporate DSG dual-clutch gearbox with a supertall seventh gear. As a result it hits 23 mpg on the highway.