Auto companies are boosting miles per gallon with smaller but still powerful gasoline engines.  And check out the cost: If you need better gas mileage but can’t afford a pricey hybrid, new cars with smaller, high-mpg gasoline engines often are less expensive as well.

To boost gas mileage while maintaining performance, auto companies are using a variety of technologies to update their gasoline engines:

  Turbocharging lets a four-cylinder engine power a car like a V-6, but only when needed.  When you hit the accelerator, the turbocharger forces more air into the cylinders, boosting power.

  Gasoline direct injection controls the timing and amount of fuel injected into the cylinders, facilitating gains in both power and mileage.

  Variable valve timing aids getting air in and exhaust gases out of the engine at all driving speeds.

  The idle stop feature shuts off the engine if you stop for a traffic light, then restarts it when you push the accelerator.

Popular Mechanics 2011 top ten most fuel-efficient small cars:

1. 2011 Kia Rio     Base Price: $12,295     MPG: 34 Hwy, 28 City, 31 Overall
2. 2011 Mazda Mazda2     Base Price: $14,180     MPG: 35 Hwy, 29 City, 32 Overall
3. 2011 Toyota Yaris     Base Price: $12,855     MPG: 36 Hwy, 29 City, 32 Overall
4. 2011 Mini Cooper     Base Price: $20,100     MPG: 37 Hwy, 29 City, 32 Overall
5. 2011 Hyundai Elantra     Base Price: $15,550     MPG: 40 Hwy, 29 City, 33 Overall
6. 2011 Ford Fiesta (SFE Pkg)     Base Price: $13,320     MPG: 40 Hwy, 29 City, 33 Overall
7. 2011 Volkswagen Jetta TDI     Base Price: $22,995     MPG: 42 Hwy, 30 City, 34 Overall
8. 2011 Honda Civic Hybrid     Base Price: $23,950     MPG: 43 Hwy, 40 City, 41 Overall
9. 2011 Honda Insight     Base Price: $18,200     MPG: 43 Hwy, 40 City, 41 Overall
10. 2011 Toyota Prius     Base Price: $22,800     MPG: 51 Hwy, 48 City, 50 Overall

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