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: AutoNews: Modern Turbos Leave Early Versions In The Dust

02-04-2008, 01:16 AM
Richard Truett

Automotive News | February 4, 2008 - 12:01 am EST

Automakers are flirting with turbochargers again, just as they have every decade since the 1960s.

Both General Motors and Ford Motor Co. recently have revealed plans to install turbochargers in mass-market cars. But the new generation of turbos won't be like the one in your father's 1962 Oldsmobile Jetfire.

The turbocharger no longer is intended to help enthusiastic drivers burn rubber or aid heavy-duty pickups that need lots of torque. Instead, it's a fuel-saving device that lets automakers use smaller engines. For example, the Lincoln MKS will be powered by a twin-turbocharged 3.5-liter V-6 that delivers the same performance as a 4.6-liter V-8.

How it works

A turbocharger is an air pump mounted in the exhaust system. It uses exhaust gases to spin an impeller at high speeds. The impeller looks a bit like the fan blades in a jet engine. It forces air through the intake manifold into each of the engine's cylinders. That enables the engine to develop a lot more power.

For most of the past 40 years, turbochargers were used sparingly in North America. GM, Ford, Chrysler, Saab, Porsche and others sold a few thousand turbocharged cars a year.

But turbochargers never enjoyed big sales because they were unrefined and unreliable. A turbo could seize up if it overheated and it often did. And if the air cleaner wasn't changed frequently, the impeller blades could be damaged. Turbocharged cars also needed more frequent oil changes.

As if that weren't enough, turbochargers offered uneven acceleration. After the driver pressed the accelerator, there was a moment or two before it spooled up and delivered the extra power. Hence the phrase "turbo lag." When the turbocharger spooled up, the car would suddenly surge forward. The impellers in today's turbochargers spin most of the time the engine is running. That's one reason why turbo lag has disappeared.

Drivers of turbocharged cars today feel a smooth rush of power. Improved performance and reliability comes courtesy of the European market, where turbodiesels are popular.

Stronger, smoother

Two parts of the turbocharger the bearings on the impeller shaft and the flow of gases to the impeller itself have received major upgrades. Better bearings don't overheat. So impellers can spool up more quickly, reducing turbo lag.

Acceleration is smoother and more predictable because of variable nozzle technology that adjusts the flow of exhaust gas to the impeller based on engine speed and load.

Suppliers such as Honeywell and BorgWarner, the leading manufacturers of turbochargers, have improved reliability so much that the device now is as trouble-free as anything else under the hood.

"We consider it to be a nonserviceable item good for the life of the vehicle," says Tom Grissom, director of business development for BorgWarner's turbo and emissions systems.

The bottom line: Turbochargers are ready for mainstream use on gasoline engines in North America.