Turbo vs Supercharged

Turbocharging uses a turbine driven by exhaust gases to compress air for the intake charge.

Supercharging uses a mechanically driven turbine, off the engine's pulley system, to drive the compressor.

Both will use an intercooler to cool the air charge so it can be enriched. Cool air burns better than hot air. Cool air also can accept more fuel vapor - i.e., it is richer.

In general, supercharging generates its compression earier on in the rpm range. Turbocharging needs higher revs to spin the turbine and create the compression. The higher the rev range, the more likely to use turbocharging. Supercharging generally has an rpm limit to its efficiency. Some applications use both for low and high rev compression. Introducing methanol can also lower the charge temperature, increasing richness and power.

Lately, turbocharging has increased its low rev efficiency through either the use of smaller turbochargers (to spin them up faster) or variable vane turbochargers that change the pitch angle of the turbine vanes for better low rev efficiency. Mechanical chargers can steal engine power to spin those turbines. Turbocharging uses "free" energy from the exhaust stream. Now that engines rev higher and turbochargers are more efficient, turbocharging is preferred by manufacturers. Generally, in larger displacement engines, manufacturers and after market tuners prefer supercharging for its greater effectiveness at lower rpms and a less complicated installation.

Lastly, superchargers generally use lower boost pressures so they make more sense as a bolt on addition. Turbochargers generally have to have the engine designed for this application to be totally efficient because they are running at higher boost pressures.

 

There are 3 (4) kinds of compressors, {roots, Whipple, centrifugal, (axial) }. The first 3 are used in automotive application to increase the charge density into what is known as a super charge.

Roots blowers create full boost at idle or just past idle, but are not 'that' efficient up top.

Centrifugal create full boost only higher in the RPM band, and do not create much boos down low.

Whipple chargers create full boost down low, but not quite idle, and run out of steam up top.

All three chargers can be driven by the crankshaft (or camshaft!). The roots is classical version of the Supercharger; the Whipple is the modern more efficient, more balanced approach; the centrifugal is easier to package to existing airflow paths and used in a lot of Mustang and pony car upgrades.

Theoretically, all three can be driven by an exhaust centrifugal turbine; however in practice only the centrifugal blowers are used with centrifugal turbines and we call these assemblies "turbos".

 

How do you drive a roots blower with an exhaust centrifugal turbine?

 

There are a few cars on the market that have both; the supercharger for low rpm until the turbo spools up...best of both worlds...no turbo lag and maximum torque throughout the rpm range.

 

Gear, belt, or ball gear-ratio reduction.

 

A Whipple is a brand of twin screw not its own blower category, The same thing would be if you called a roots type an Eaton.

 

In simplest form:
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Although related to Roots, Whipple has significantly better adiabatic efficiency compared to a roots. The airflow is compressed by a different mechanism, and the sealing of the pressurized air is by a different mechanism.

 

Too much detail. He just wanted to know the diff between the 2 boosting options. The variations between supercharger systems is beyond the scope. I didnt even bother with helmholtz effect!