Forced Induction Turbo vs Supercharger

Turbo vs Supercharger

Taken from 9thgencorolla.com (http://9thgencorolla.com/forum/showthread.php?t=26714) for information purposes for those of you with questions about what the differences are between a turbo set up and a S/C.


The Comparison: Turbocharger vs Supercharger
Response. Superchargers afford the engine immediate response since the supercharger is always compressing intake air, provided that the engine is rotating. Although this initial boost is very small, it's growth is gradual with increased engine speed, resulting in a smooth increase in power. Turbochargers, on the other hand, suffer from what is refered to as turbo lag. Becuase of the inertia of the turbocharger rotating assembly, the turbo must "spool up" before it is able to compress air, so there is no power increase at low engine speeds, as the turbo impeller starts rotating. At WOT (wide-open throttle), there is usually a very sudden increase in turbo boost at a certain RPM range (typically near 3000 RPM). If you've ever driven a turbocharged vehicle, you probably know what this kick in the pants feels like. Turbochargers can also be sized so that faster response is acheived. For example, diesel engines use turbochargers which are small enough to spool by 1700-2000 RPMS. The trade-off is that maximum power can't be reached with such a small turbocharger.

Parasitic Power Loss. Becuase superchargers are driven by the crankshaft, they draw some of the power which the crankshaft would be producing to compress the intake air. Of course, the supercharger is more than making up for the power it uses by introducing additional air. Turbochargers, however, do not use any of the crankshaft's power in order to operate. Turbos are often described as exhaust restrictions, though. The argument is that the increased exhaust backpressure presented by the turbo also robs power from the crankshaft (since it is now harder to push the piston up to expell the exhaust gases). Because the intake air is also under pressure (typically greater pressure until the maximum horsepower engine speed), it pushes the piston down. For the majority of the power band, these two forces cancel on another out. Because turbochargers do not use much of the power output of an engine, the highest power levels are possible when using a turbocharger rather than a suprecharger.

Heat Production. Cooler intake air is denser - which means more oxygen per unit volume. More oxygen means more power. Roots blowers are notorious for their heat production. This heat production is a result of inefficient compression of the intake charge. Turbochargers tend to operate at a much better efficiency than thest upes of superchargers. Centrifugal superchargers can be just as efficient as turbochargers, and offer the advantage of flexibility in placement. Turbochargers must be placed so that the exhaust flows through the turbo's turbine. This brings the hot exhuast pipes closer to the intake pipes - resulting in higher intake temperatures. A well designed centrifugal supercharger installation can reduce this heating, resulting in a cooler intake charge.

Reliability. People often say that superchargers are more reliable than turbochargers. Because turbochargers operate at such high temperatures and are oil lubricated, if they are not allowed to cool down before the engine is turned off, the oil can bake inside the turbocharger. This can result in shorter turbocharger life. However, with proper care and cool down, a turbocharger can last as long as an engine.

Boost Levels. For absolute maximum power applications on stout engines, turbochargers allow much higher boost levels than superchargers. In tractor pulling, to take the example to the extreme, up to three turbochargers are used in series to produce boost levels of up to nearly 200 psi!

Conclusion: Turbocharger or Supercharger?
You can see that it is difficult to say which is better. The main advantages to supercharging are low-end response (not the case with centrifugal types) and simplicity. The main advantages to turbocharging are efficiency and the realization of maximum power. It is up to the vehicle owner to decide which solution is best for him or her.