How large an engine do you need in a mid-size car?

Just a few years ago, the answer would have been a V-6 of 2.8 to 3.5 liters, perhaps with a base model offering a four of 2.4 to 2.8 liters.

Then Hyundai announced in late 2009 that it would abandon V-6 engines altogether for its 2010 Sonata, fitting only fours. The base Sonata engine is a 2.4-liter four putting out 175 hp.

But how small can you get? And how many horsepower do you need? Would, say, 160 hp be enough?

A 2009 Volkswagen Passat wagon, used as a test bed for "radical downsizing" and shown in Germany by Bosch Mahle Turbo systems, generates 161 hp and a peak torque of 210 foot-pounds across a wide range of engine speed from 1600 to 3500 rpm.

2009 VW Passat wagon test car for Bosch-Mahle turbocharged 1.2-liter, 3-cyl engine, courtesy Ward's

2009 VW Passat wagon test car for Bosch-Mahle turbocharged 1.2-liter, 3-cyl engine, courtesy Ward's

So is it a 2.0-liter four? Perhaps a turbocharged 1.6-liter engine, similar to Ford's upcoming EcoBoost four?

Nope. Not even close. That power and performance came from a three-cylinder turbocharged engine with a mere 1.2 liters of displacement.

What about gas mileage? In the Passat test car, the engine is rated at 40 miles per gallon on the European test cycle. That would likely translate to 32 to 35 mpg on the U.S. combined cycle.

Which is pretty good for mid-sized five-passenger station wagon, no?

2009 VW Passat wagon test car for Bosch-Mahle turbocharged 1.2-liter, 3-cyl engine, courtesy Ward's

2009 VW Passat wagon test car for Bosch-Mahle turbocharged 1.2-liter, 3-cyl engine, courtesy Ward's

This is just another example of the development of much smaller, more efficient engines that produce the same power as larger ones but from far smaller sizes--and deliver vastly better fuel efficiency in the process.

Among the manufacturers planning or launching such engines are Ford (across its successful and growing range of EcoBoost engines), BMW, Fiat, Buick, and others.

And both BMW and Ford are planning three-cylinder engines, a first for each maker.

With U.S. corporate average fuel economy rules potentially requiring gas mileage as high as 62 mpg by 2025, carmakers know they have to wring a lot more miles out of each gallon of gasoline.

But as demonstration projects like the 1.2-liter turbo Passat show, there's a lot of life left in the gasoline engine yet.

[Ward's]

+++++++++++

Follow GreenCarReports on Facebook and Twitter.