New Gas Mileage Rules Will Reshape What Americans Drive: Engines And Transmissions

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VW logo and sign at opening of Volkswagen engine plant in Silao, Mexico

VW logo and sign at opening of Volkswagen engine plant in Silao, Mexico

Smaller, more efficient engines better matched to more complex transmissions will have some of the biggest effects in making tomorrow's cars more fuel-efficient.

The 2025 corporate average fuel economy (CAFE) level of 54.5 mpg translates to about 42 mpg on the EPA window sticker.

And while Toyota Prius hybrid owners may note that they can do better than that today, the average applies to all vehicle types--not just small cars but even full-size pickup trucks.

Reduced weight and lower wind resistance will play a role in getting your next vehicle to deliver better gas mileage than ever before, no matter how large or small they are.

And many of the changes will come in engines and transmissions.

This is the second of three articles on the future technologies that will boost fuel efficiency in future cars.

So what will those changes consist of?


Engine efficiency improvements may be the single biggest factor in improving gas-mileage ratings for the next few years.

A variety of technologies--direct injection, variable valve timing and valve lift, even electrically actuated valves--are already making combustion more efficient.

That permits what's known as "downsizing": an engine, frequently with fewer cylinders, that's smaller, lighter, and has fewer moving parts--which reduces fuel-wasting internal friction.

To make up for fewer cylinders, many of these engines are turbocharged--using otherwise wasted exhaust heat to power a pump that packs more air into the cylinder.

The resulting higher air pressure can be combined with more gasoline, meaning the engine produces more power on combustion.

That gives these engines higher horsepower for their size than "regularly aspirated" engines, meaning a four can perform like the V-6 it replaces.

In other words: Don't count the gasoline engine out for many years to come.

2011 Ford F-150 EcoBoost rear view - Drive Tour 2011

2011 Ford F-150 EcoBoost rear view - Drive Tour 2011

Example: EcoBoost

The best example of this is Ford's line of EcoBoost engines, which started with a 3.5-liter turbocharged V-6 with the same power and towing capacity as the larger V-8 it replaced in Ford's best-selling F-150 pickup truck.

That engine has been a surprise, selling much better than Ford expected, especially in full-size pickup trucks.

It was joined by a 2.0-liter four that replaces a 3.0- to 3.5-liter V-6, and then by both 1.5- and 1.6-liter fours that replace larger standard 2.5-liter fours.

Most recently, Ford has added a 1.0-liter three-cylinder turbocharged engine, which replaces a conventional four of up to 1.6 liters.

And, who knows, there may be more to come.

The downside of smaller turbo engines is that they're more economical under light load than the bigger ones they replace, but equally thirsty at high power.

So aggressive drivers may find them thirstier than their EPA ratings, while gentler souls do just fine.

Few V-8s outside trucks

By 1970 or so, even so-called compact sedans offered V-8 engines. The only sixes were on base models, and four-cylinder engines from U.S. makers were a rarity.

2011 Hyundai Sonata 2.0T

2011 Hyundai Sonata 2.0T

The rapid market gains achieved by smaller, more fuel-efficient, and better-built Japanese cars taught Detroit a 20-year lesson.

Now, if anything, some categories of U.S. cars use smaller engines than their Japanese competitors.

Big V-8s these days are limited to full-size pickup trucks--all of which come with V-6es as the base engine now--and a handful of pony cars and high-end large sedans.

The V-6 has effectively taken the place of the V-8, but it's really four-cylinder engines that are now the norm.

Andthey can be much larger than the 1.2- to 1.6-liter "econobox" engines that some buyers still imagine them to be.

Fours are the default

Around 2010, makers began to get rid of their V-6 options in both mid-size cars and compact crossovers, and the trend has accelerated rapidly.

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