Don't Let More Air In Than You Need
The more "slippery" a vehicle is through the air, the more fuel efficient it will be at highway speed. Air friction is a big deal when you move fast, so anything to reduce it can make a difference. The biggest factor is of course the overall shape of the vehicle, but there are all kinds of other tricks to lower the drag coefficient. One of those tricks is to have a variable geometry air shutter at the front of the vehicle, something that the Chevy Cruze Eco will have. By changing the size of the air inlet, this system can either make the car more aerodynamic or provide more cooling to the engine depending on driving conditions.
Cars that don't have such a system force engineers to plan for worse case scenario, which is usually something like towing in the desert heat, something that few of us ever do. This leads to cars that are less slippery than they could be.
GM claims that this simple system makes a difference of about 1 MPG on the highway. It might not seem like much, but when combined with lots of other fuel-saving techniques (engine downsizing, weight reduction, low-rolling resistance tires, idle-stop, direct injection, etc), it can add up to significant savings.
All cars such have a variable geometry air intake system. A few more dollars when the car is built could save many more dollars at the pump over the life of the vehicle, not to mention all the CO2 that wouldn't go in the atmosphere.
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