Turbocharger or Supercharger?

Let’s start at the beginning; both turbocharging and supercharging are force induction systems – that is they force the air into the engine at a much higher pressure than the naturally aspirated systems.

Forcing more air into the combustion chamber allows the engine to burn more fuel during its power stroke and consequently produce more energy. Both superchargers and turbochargers therefore have the same goal – producing more power, the difference lies in how they go about it.

The biggest and the most obvious difference between the two systems is where they derive their power from. Superchargers are powered by the engine’s crankshaft while turbochargers get their power from the engine’s exhaust gases.

Supercharges draw power from the crankshaft via a chain, gear or bell and pulley system.

Because turbochargers are using exhaust gases expelled by the engine they do not need to use any of the engine’s existing power to operate. This is in a stark contrast to superchargers that use a portion of the engine’s power output to perform their duties.

Turbochargers are powered by the exhaust fumes expelled from the engine.

Splitting Hairs
There are two main types of superchargers: a centrifugal type and a positivide displacement (Roots or Lysholm Screw) type. A centrifugal type supercharger is very similar to a turbocharger with the notable exception of being connected to a crank via a belt and pulley system. The air is drawn into the supercharger, compressed via an impeller and discharged into the engine’s intake.

Very similar in its internal construction to a turbocharger, a centrifugal supercharger (above) is considered to be the most efficient of all superchargers.

Roots supercharger (named after its inventors – the Roots brothers) produces its boost via a pair of overlapping lobes that force the air down into the intake.

Twin Screw supercharger works by pulling air through a set of counter rotating, high tolerance screws.

In the case of a Roots or Lysholm Screw (aka Twin Screw) type supercharger the compression is done via a counter-rotating rotors (Roots type) or twin rotating screws (Twin Screw type). The faster the crank speed – the more boost is produced. The biggest advantage of superchargers is that they produce a very linear boost, all the way from a very low RPM.

A turbocharger (see image below) consists of two halves: The compressor and the turbine. The exhaust gases spin the turbine, which is connected via a common shaft to the compressor. The compressor then forces air into the engine. Because the operating speeds of a turbocharger can be up to 10 times those of a supercharger it can produce more boost in a shorter time.

The good and the bad
Anyone interested in turbos would have heard of the dreaded “turbo lag”. Because turbos derive their operating power from exhaust gases, before it starts generating boost the turbine must first spool up. The delay between the turbine’s idle speed and its full throttle speed is called a “turbo lag”. Over the last decade the advances in turbo technology have all but eliminated the “turbo lag” and it’s not that much of an issue nowadays.

In contrast, a supercharger, being connected directly to the crank, produces boost almost immediately, even at very low RPM. This is especially evident on a roots and screw-type superchargers.

The turbo lag has been almost totally eradicated in modern turbo systems.

What superchargers gain in their boost delivery department however, they lose when it comes to efficiency. While turbochargers do create some additional exhaust backpressure and interrupt the exhaust flow, they do not drain any power away from the engine itself. Their main source of operating power comes from exhaust gases that are already being expelled by the engine.

This makes turbochargers much more efficient in creating boost than superchargers that rely on the engine’s crank to provide them with operating power with the demand for power growing along with the amount of boost being created.

Another area in which the turbochargers have a distinct advantage is flexibility. Using various add-ons like wastegates and boost controllers, a turbo can be tuned to produce a specific amount of boost at any given time. Boost levels can be specified by gear, time or a simple push of a button, all in real time.

In a turbo system, boost can be controlled via a combination of various add-ons like wastegates and boost controllers.

In contrast, to change the boost rating of a supercharger its pulley system needs to be changed. This requires time and obviously cannot be done while operating.

In the area of reliability superchargers have been, until recently, considered superior. With the advent of new technology and new, exotic materials, turbochargers have forged ahead into many motorsport areas traditionally dominated by superchargers. Although they are more complex in nature and require more modifications to the engine, turbo systems are also capable of much higher boost and therefore extracting a much higher peak power than superchargers.

Turbochargers are starting to take over many motorsport fields traditionally dominated by superchargers.

So which is system is better? Before we answer this, we really need to rephrase the question to: “Which system is better for ME?” because that is exactly the crux of the issue. Each system has its good and bad points and each performs in its own unique way so your choice really needs to be guided by what YOU want it to do.

Turbochargers are lighter, smaller and more tuner-friendly. If you size them properly you can successfully turbocharge just about anything from small capacity imports to big capacity domestics and diesels. There are many Turbo Kit manufacturers that offer bolt-on kits to suit specific makes and models making turbocharging your car easier than ever.

On the other hand, there are still many people who will prefer the immediate response and ease of operation of a supercharger so your choice will really come down to what suits your application better and which system will better address your needs.

Read more:
Forced Induction 101
History of Turbocharging