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Turbochargers: Sumpin' Fer Nuttin'

Turbochargers: Sumpin' Fer Nuttin'

In a previous article I alluded to the use of turbochargers to boost diesel power output and mentioned the need to explain later how they work. Well it's time to talk HOT AIR, and if anyone knows about hot air it's me!

A long time ago engineers realized that when more air is shoved into an engine, then, with added fuel, they could get more power out. They figured out a way to use some of the engine's power from the crankshaft to turn a compressor that would literally ram more air into the engine. This process is known as supercharging. A classic example is the almighty Mercedes 540K of the mid-thirties, with it's 5.4 liter engine rated at 120 horsepower (HP) in "Clark Kent" mode, and 180 HP in "Superman" mode when the pedal was mashed to the floor. A modern example is the SLK230 Kompressor with it's supercharged 4-cylinder engine. Oh yeah, the topic is actually turbochargers.

Somewhere along the line someone figured out that the hot gases exhausted from an engine at a high velocity could be used to generate more power. Imagine if you will, two sets of fan blades rotating on a common shaft. One fan is placed in the exhaust gas stream and the other set of blades sits in the intake air stream. The exhaust fan is caused to spin at a rapid rate by the high speed exhaust; thereby, causing the intake fan to spin at the same rate, compressing and shoving more air into the engine. Add more fuel at the right rate and voila, MORE POWER, which is about as close as we can get to something for nothing. There is one catch (There always is!) and it's known as "turbo lag". The turbo needs to spin very rapidly, up to 100,000 RPM, to effectively boost the power output of an engine. Off the line a turbocharged engine will act just like it's normally aspirated brethren, but at about 2,000 RPM crankshaft speed the turbo power kicks in and WHOOPEE! Just ask Jim Gallimore about his turbocharged 300D.

A word about the care and feeding of turbos. Since engine oil is used to cool and lubricate the turbo's bearings, proper oil level must be strictly maintained and the oil should be changed more often. After a spirited drive on our American autobahns, the engine should be idled for a minute or two before shutting down, to let the turbo revs drop. If this is not done the turbo's bearings could be cooked! Big $$$$$. While other manufacturers have had premature failures, Mercedes turbos can last 200,000 trouble-free miles. Just ask Jim Gallimore about his turbocharged 300D.

Remember, if you have a question about the care and feeding of your Mercedes pride and joy, please feel free to call or write.

Steven Rae, Technical Advisor

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