Auto Consultants

Turbocharging versus Supercharging

See also: Bolt On Turbo Kit

Turbocharging & supercharging has been in existence for decades (supercharging even in World War 2) and has been misjudged by many as unreliable. Such misinformation has been perpetuated by many small workshops mainly through their ignorance about new turbo-charging technologies available today. While it might true in the 70s & 80s when the turbo was first introduced to street cars, turbocharged cars in the 21^st century have made a huge leaps in terms of reliability and durability. Take a look at what car manufacturers are offering today. Most marques if not all of them have either a turbo-charged or super-charged models. In fact, the technology has moved further as VW has incorporated both supercharging & turbocharging technologies into their engines to capitalize on the strengths & weaknesses of both technologies.

In order to make more power or torque from an engine, it needs to breathe more air & fuel mixture. One method is to increase engine capacity which requires a larger engine compartment and an increase in the weight of the vehicle. Most countries slap a higher tax on high capacity engines as they are detrimental to the environment. The use of turbo charging is to force more air and fuel mixture into the engine. A 2000 cc engine using turbo technology can provide the power and torque of a 3000 cc or even more through some tweaking as we will see in this article. As a rule of thumb, every 1 psi of boost pressure increases power by 7%. Even with ‘ low’ boost levels of 7psi or 0.5 bar, you will get an increase of close to 50% power increase.

A turbo is basically an air pump which pushes more air into the engine. It consists of an exhaust turbine and is link by a shaft to a compressor turbine. The turbo uses the normally ‘wasted’ gases of the exhaust to spin the exhaust turbine which in turn, spins the compressor turbine. The high speed of the turbines which spins up to 280,000 rpm causes the compressor turbine to forces air into the combustion chamber. Turbo-lag is hesitation of the engine before the turbine spins up enough to provide sufficient air flow. As the compressor turbine compresses the air that is forced into the engine, compressed air heats up which impairs the development of more power. Cool air is more dense and has a larger volume of oxygen. In order to cool down this ‘heated’ air, an intercooler which essential is an air radiator, is used to reduce the temperature of the air. This will released an additional 5 to 15% of power and torque to the engine.

Unlike a turbo, the supercharger is driven by a belt powered by the engine just like the aircon compressor. Because it is driven by the engine and suffer ‘parasitic’ losses of 10 to 15%, the supercharger is ‘less’ efficient than turbos. Two basic types of superchargers are Centrifugal and Roots with the latter more popular on street cars as evidenced on cars such as Mercedes and other European models. The Roots supercharger has better characteristics in terms of faster delivery of air and this translates into faster response & torque for driveability. Street cars need their torque earlier in the rpm bandwidth for better response instead of later as compared to a high performance sports model where high revs is the order of the day. However, one major complaint of the Roots superchargers is of its high pitched whining sound.

The Centrifugal Supercharger essentially is a turbo driven by a belt and its characteristics is very linear as the boost levels depends on the engine rpm speed. As an example, the boost characteristics is 2000rpm 1psi, 3000rpm 2.2psi, 4000rpm 3.8psi, 5000rpm 5.2psi, 6000rpm 7.5 psi etc. This means that for the Centrifugal Supercharger, you would have to rev the engine to achieve the boost levels. However, despite the characteristics of Centrifugal Superchargers, aftermarket tuners are more than often using Centrifugal Superchargers due to its smaller packaging, quietness and easy to fit profile.

One thing, many forumers and workshops claims that LTA will confiscate the car for illegally fitting a supercharger whereas for a turbocharger, it is the same penalty as an illegal exhaust modification. They have been mistaken. In fact, the best people to verify would be LTA. You can call or email LTA and they will be most happy to let you know. Of course, they will tell you that it is illegal to fit one without the approval of the car manufacturer.