OPEN DISCUSSION TOPIC VI

Supercharging vs. Turbocharging:  Extinct?  Exotic?  or Extraordinaire?

We have seen them come and have seen them go, we have witnessed the performance on the track, we have felt the performance in our daily cars but why does Supercharging and/or Turbocharging an engine seem like such a rare science which we rarely see on performance cars?  These little boxes of high winding turbines spinning gases into such awesome forces fed into engine intakes and creating a fearsome whirl for those around us - yet so distant to either our desires or our budgets.  Do you realize these high-tech words are nearly as old as the internal combustion engine itself?  Let's look at these technologies and address the evolution to where we are today.

Turbocharging

Turbocharging by definition is simply using the engine exhaust gases to spin a turbine to in-turn rotate a compressor to force air into the intake of the engine at a high velocity.  When air is forced into the engine, the engine must rapidly 'digest' the air which produces a rapid increase of engine revolutions (RPM) and thus an instant boost in horsepower.  So simple a concept, yet so technical in nature in the equations for exhaust to clean air ratios and turbine fan and compressor fan blade design.  The turbocharger was invented by Swiss engineer Alfred Buchi for the internal combustion engine and applied for a patent in 1905¹.  Did I mention these have been around for awhile?  Commercial applications found there way on steam ships and locomotives in the 1920's¹.  To increase high altitude engine power applications for military aircraft turbochargers were incorporated in the 1930's.  By the late 1940's experimentation on automotive race tracks was taking place and by 1952 the Indianapolis 500 Pole Position winner, Fred Agabashian, used a turbocharger¹.

As time advanced, we finally found our first OEM automotive turbocharger in the Oldsmobile Cutlass and Chevrolet Corvair in 1962.  Since then turbocharging has never become much more than a novelty for the automotive world.  We have seen GM, Chrysler, Datsun, SAAB, and Porsche among a few of the developers of the turbocharger for automotive applications.  Most notably Buick in 1978 released their V-6 with a turbocharger and then increased in advancements until they reached 300 horsepower with the turbocharger and challenged the Chevrolet Corvette as the top US performing factory vehicle.

Let us take a look at the art of turbocharging.  As stated by Garrett (turbo manufacturer) in their Introduction to Turbocharging, "Engine power is proportional to the amount of air and fuel that can get into the cylinders.  All things being equal, larger engines flow more air and as such will produce more power.  If we want our small engine to perform like a big engine, or simply make our bigger engine produce more power, our ultimate objective is to draw more air into the cylinders.  By installing a turbocharger, the power and performance of an engine can be dramatically increased."²  Review the diagram below to see the flow of air using a turbocharger.

Supercharging

Much like Turbocharging, Supercharging accelerates the velocity of air into the engine intake.  By definition...a method of introducing air for combustion into the cylinder of an internal combustion engine at a pressure in excess of that which can be obtained by natural aspiration.¹  Unlike the turbocharger, the supercharger is using all 'clean' air where the turbocharger derives its energy from spent exhaust gases.  Look at how closely related the history of supercharging is to turbocharging.

In 1900 Gottlieb Daimler (of Daimler-Benz fame) became the first person to patent a forced-induction system for internal combustion engines.  His first superchargers were based on a twin-rotor air-pump design first patented by American Francis Roots in 1860. We have heard of the 'Roots blower' over the years.  This design is the basis for the modern Roots type supercharger.³  The first automotive applications were in the 1920's with the Bentley and Mercedes Benz vehicles.  The compressed gases caused a higher rate of wear on the engine thus reducing engine life.

The supercharger relies on power from the engine, typically a belt drive, to rotate the compression shafts for the supercharger.  So, essentially we are robbing power from the engine to create more power through the high velocity intake of air into the engine.  

Check out this great list of Questions and Answers about superchargers from Blower Drive Services (BDS) www.blowerdriveservice.com.

The Differences............

Engine induction has seen many sciences and a lot of human development hours have been spent on maximizing fuel efficiency and engine power.  In addition to turbocharging and supercharging there is natural aspiration (carburetor), fuel injection, nitrous and water injection and many variations incorporated several of these technologies together.  Superchargers are mounted right on top of the engine intake as opposed to turbochargers mounted under the hood where they can fit best and then pipe fed to the engine intake.

The thermal efficiency, or fraction of the fuel/air energy that is converted to output power, is less with a mechanically driven supercharger than with a turbocharger, because turbochargers are using energy from the exhaust gases that would normally be wasted.  For this reason, both the economy and the power of a turbocharged engine are usually better than with superchargers.³  Superchargers just plain look cool, turbochargers look complicated.  Turbochargers appear more sophisticated in nature due to the amount of piping which must be fabricated.  Superchargers are a way to achieve that BIG engine appearance, you have seen it - the hot rod with the engine height taller than the roofline.

Where have they all gone?  Why aren't more people using these technologies as a quick boost in horsepower?  Cost?  Too much power?   Too poor fuel economy?  Like to keep everything 'under' the hood?

These are classic technologies that forever seem to be brushed aside as only a few people have actually used these on their cars.  It appears this trend will continue even though both of these options are derived from the existing engine power to create additional power.

What are your thoughts on Supercharging or Turbocharging?

J. Shelton

References

1  Turbocharging, Answers.com (www.answers.com)

2  Turbo Tech 101 (Basic), Garrett (www.turbobygarrett.com)

3 Supercharger, Wikipedia (www.wikipedia.com)