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Tuning Guide

 

 


Forced Induction 101

An engine produces power by igniting fuel and air inside a chamber. As the fuel and air are ignited, the pressure within the chamber increases, applying a force onto a piston or rotor. The generated force is applied on a crank shaft which causes rotation. How much power generated is mainly determined by how much fuel and air is ignited inside the chamber to produce the driving force.

There are two types of induction systems for combustion engines; naturally aspirated and force-fed (forced induction) engines.

Naturally aspirated (N/A) engines draw in air for combustion under atmospheric conditions. As the piston moves down, the intake valve opens allowing the piston to suck air into the chamber. How well the chamber is filled is called its volumetric efficiency.

A volumetric efficiency of 100% means that the chamber is completely filled with air compared to the chamber at static conditions. The volumetric efficiency of a naturally aspirated engine can never be higher than 100% the engine cannot fill the chamber more than under static conditions due to the air pressure being the same. Its ability to fill the chamber is also greatly affected by how long the intake valve is open for and how fast the engine is rotating.

Forced induction engines use a pump to increase the air pressure entering the engine and therefore increasing its volumetric efficiency. Higher air intake volume allows for more fuel to be burnt which increases the amount of power generated by the engine.

There are 2 different types of pumps in forced induction systems; a turbocharger and a supercharger.

A turbocharger (above) is an air pump which is driven by exhaust gases exiting an engine. It consists of a compressor that is connected to a turbine via a common shaft. The compressor is essentially a fan within a housing which takes in air through the center and forces it out of the housing at an increased pressure and velocity into the intake manifold of an engine. The turbine is another fan which has exhaust gas from the engine, pushing on the blades which cause it to spin. The exhaust gas then exits out of the center of the turbine.

A supercharger (above) is a compressor which is directly driven by the engine via a belt and pulley system. As the engine RPM increases, the compressor RPM increases, pushing more air into the engine. Supercharged engines tend to have linear power delivery compared to turbocharged engines as the rotational speed of the compressor of the supercharger increases linearly.

A small engine equipped with a turbocharger or supercharger has the ability of produce the same amount of power as a large capacity engine without the associated fuel consumption. For example, a turbocharged 2.0L engine at low RPM off boost will consume similar amounts of fuel to a Naturally aspirated 2.0L engine. A large 6.0L engine even at low RPM will consume more fuel than the 2.0L engine but when the 2.0L engine is on boost, then the power generated can be the same as the 6.0L engine which means the fuel consumption will be similar. The fuel saving is when the smaller engine is off boost, it performs like a small engine and consumes fuel like a small engine but when it is on boost, then it performs like a large engine.

Another benefit of a forced induction engine is the ability to increase its performance. To improve the performance of a N/A engine, its volumetric efficiency needs to be increased as this is what allows more air to be ingested by the engine to create more power. Increasing the maximum RPM will also increase its performance.

To increase its volumetric efficiency requires changes to cam shafts, inlet tracts, exhaust systems etc. The increase in power will only be marginal as most engines are fairly efficient from factory. In terms of ease and performance compared to cost, a forced induction engine is best.

The performance of a turbocharged engine can be increased greatly just by increasing the boost or controlling where maximum boost is reached. Simple modifications such as larger exhaust systems and free flowing air filters can yield large power increases compared to doing the same modification to a N/A engine.

* Article retrieved from: http://www.turbosmartusa.com/technical-articles/forced-induction-101

 


How does a Wastegate work?

What is a wastegate
Internal or external, a wastegate is a boost-controlling device that operates by limiting exhaust gases going through the turbocharger, controlling the maximum boost pressure produced by the turbocharger itself. A wastegate consists of an inlet and outlet port, a valve and a pressure actuator.

How a wastegate works
A pressure actuator, controlled by boost pressure determines whether the wastegate is open or shut. In its resting position, a wastegate is shut, and as the boost pressure builds, force is applied to the actuator. When the boost pressure exceeds the spring value, the actuator will progressively open the wastegate, bypassing some of the exhaust gases therefore maintaining the boost pressure at the set level. To put it simply – a wastegate prevents the boost pressure from climbing indefinitely and consequently blowing the engine.

When is an external wastegate needed
Most of the factory turbo systems feature an internal wastegate made to handle stock boost levels. The most common reason for investing in an external wastegate is fitting an after-market turbo or better control of the boost and consequently the power output of your engine. Additionally, most large frame turbochargers are not equipped with internal wastegate systems.
Most tuners will recommend an external wastegate for any engine producing 400hp or more, as running high boost through a factory internal wastegate can overpower the actuator spring, limiting maximum boost level. Aftermarket external wastegates feature bigger inlet and outlet ports, higher pressure springs and bigger actuator diaphragms to effectively control high boost pressure.

* Article retrieved from: http://www.turbosmartusa.com/technical-articles/how-does-a-wastegate-work

 


With so many contradicting opinions and recommendations, it’s a little wonder choosing the right wastegatefor your application can be a confusing. We try to disspell some myths and shed some light on the most common misconceptions regarding wastegates.

TRUE OR FALSE

The more powerful the engine, the bigger the wastegate you need

False. This is one of the more popular misconceptions. A wastegate is possibly the only component in your whole engine package that can actually be made smaller as you increase your boost/horsepower output. Use this simple guide:

Big Turbo/Low Boost = Bigger Wastegate
Big Turbo/High Boost = Smaller Wastegate
Small Turbo/High Boost = Smaller Wastegate
Small Turbo/Low Boost = Bigger Wastegate

Wastegates don’t operate in high temperatures.

False. Contrary to the popular belief, external wastegates are usually mounted at the hottest part of the exhaust. It’s the place where all the exhaust gases meet, creating extra heat. This, combined with the late combustion of unburnt fuel (due to rich mixtures, retarded timing and high octane fuels) significantly raises the exhaust temperature.

Larger wastegate valve diameter = better flow.

True – sort of. While the valve diameter is without a doubt an important part of the flow rate, equally important, but often misunderstood, is the importance of the flow path. When comparing wastegates with similar valve size, it is important to have a balanced body/valve/spring combination that is designed to work together to allow for maximum boost control. All Turbosmart wastegates are designed with this in mind.

* Article retrieved from: http://www.turbosmartusa.com/technical-articles/wastegate-myths