HOMEBeginners guide to tuning3. FORCED INDUCTION

Beginners guide to tuning

Forced Induction

What is a Turbocharger?

Using the energy from the engine exhaust gasses, blades like those found in a windmill are turned with a compressor which attached on the same axis. This compresses air and forces it into the engine allowing for higher outputs to be gained from the engine. The amount of air (pressure) forced into the engine is referred to as boost pressure and this can be adjusted by controlling the amount of exhaust gas which passes through the turbo. This adjustment is performed by the use of a bypass valve which is between the engine and turbo and can release the exhaust gas without flowing through the turbo. This is activated by the compressor pressure.
 By raising boost pressure the engine is able to take in more air but due to limitations in engine strength and extreme combustion (known as detonation or knocking) boost pressure is limited. Stock boost pressure is normally restricted with a large margin of safety to cope with a wide variety of uses and also for environmental reasons.

2 Types of Bypass valve

Actuator TypeWategate Type

Bypass valves fall into 2 main types. Actuator types and wastegate types. Both work by opening a bypass valve when the designated boost level is reached and allowing the exhaust gas to escape without flowing through the turbo which prevents boost from rising further. They both perform the same job but the actuator is compact and can be made as one with the turbo unit, whilst the wastegate requires piping and fitting before the turbo, bypass capacity can be made larger on a wastegate type giving more stable boost settings. From these characteristics, it is common that actuators are used on stock and smaller turbos whilst wastegates are used on larger turbos for higher power applications.


What is "Boost Up"?

By increasing the amount of forced air into the engine, the explosive force is increased thus increasing engine output. "Boost up" increases the conservative stock boost levels to release the full potential of the stock setup. The most common way to raise boost is to fit an EVC (Electronic Valve Controller) boost controller. It is also possible to replace the actuator for one with a stronger spring. Although Boost up is a relatively simple way of increasing power, there are many possible complications such as knocking fuel control or boost cut that could lead to possible engine damage and so it is important to be aware of the vehicles capabilities.


What is "Turbo Swapping"?

Turbo swapping is the next step up from boost up. The limitations of the stock turbo can be easily reached and for those who require more can replace their turbo for one which can handle more air flow.
 Normally, one would think that with the same engine and boost pressure, a small turbo and large turbo would both produce the same amount of power. However this is not the case and the larger turbo will produce more power. This is caused by the difference in turbo efficiency as each size turbo has a boost pressure (air flow rate) that it can work most efficiently at and using inefficient boost pressure will cause a rise in air temperature reducing air density thus reducing the amount of air into the engine even at the same boost pressure.

What is an Intercooler?

An Intercooler is a heat exchanger (cooling device) which is designed to cool air which has been heated by the turbo during compression.
 Popular tuning in this field involves the addition or replacement of the intercooler for one of higher capacity and efficiency. A good intercooler must be able to reduce the resistance to air flow (pressure loss) and also reduce the air temperature as much as possible. These are two opposite properties and so it is difficult to achieve both together. HKS have continued to develop intercoolers in the pursuit of achieving both criteria.


What is a supercharger?

As opposed to a Turbocharger which uses exhaust gas power, a supercharger borrows a little power directly from the engine to operate a compressor. Specifically, it is most common to use a belt and pulley from the engine crankshaft to turn the compressor. As a result, the compressor will work from low rpm giving good response from the moment the accelerator is depressed. With a turbo which uses exhaust gas flow there is a delay before the exhaust gas flow necessary to operate the compressor is generated. However, at higher engine speeds (rpm), superchargers which use engine power, tends to becomes less efficient than a turbocharger.

Common Supercharger types

Roots Type: 2 rotors mesh together and push air out of a housing. Most conventional superchargers are of this type. Since a roots type supercharger does not compress air inside within the unit, a larger housing can be required for big power outputs.

Centrifugal Type: Shaped like a turbo but is driven directly by the engine rather than by exhaust gas. The internal structure divides into several further subgroups. HKS uses what is referred to as "Torque Reaction Drive Type" and with internal compression and traction drive mechanism, is able to provide suitable compression at all engine speeds.


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