Forced induction is the compression of air into the intake manifold of the combustion engine. When a stock engine is runnning it is not consuming it's full potential of air. When the concept of forced induction was introduced the engine was able to gain power by gaining more oxygen. The combustion reaction is fueled by three things air, fuel and heat. If an increase in air or making the air more dense would intensify the reaction. The three ways used to make this possible are the supercharger, the turbocharger and the intercooler. Each plays it's own role in creating a forced induction engine able to produce almost 50% of the total power of the engine.
The combustion engine needs three things to work, air, spark and fuel. If there were an increase any one of these their would be a direct change the the performance of the engine. Air has the ability to produce more power without having improving the spark or fuel. The air system or induction system sucks air into the cylinders along with fuel. In an engine there are intake valves and exhaust valves each has a specific purpose. When the piston moves down the cylinder, fuel and air come in through the intake valve. Combustion takes place when the piston rises and compresses the air. Immediately the exhaust valve opens and the exhaust is pushed out, the exhaust valve then closes and the intake valve opens once again. Between the time when the intake valve opens and closes air enters the cylinder this is a very short time frame. As you can imagine the full capacity of the cylinder is not reached. This is where forced induction come to aid. With forced induction the air is literally forced down into the cylinder. A compressor is used to compress the air before the air is allowed into the intake manifold where the intake valves are. This fills more of the capacity of the cylinders with air. More air makes the combustion more powerful than when sucking air into the cylinders. The combustion reaction between gasoline and air,C8H18+O2=CO2+H2O, will be greatly affected when more air is introduced to the reaction. It makes that reaction much more powerful way. The compression of oxygen along with the hydrocarbons(gasoline)produces more power making forced induction a chemical process and a very popular car performance enhancer.
Superchargers are one of the ways of compressing air into an engine. A supercharger is belt driven, meaning it has a pulley system that connects it to the crank shaft. In most cases the pulley on the supercharger is smaller than the pulley on the crankshaft so that it can spin at higher rpms than the crankshaft. inside the housing of the supercharger there is a turbine that spins at the same rate as the pulley, this turbine is what creates the term forced induction. As the turbine spins it compresses air into the intake and creates boost. As the crankshaft begins to turn so does the supercharger making the supercharger an instantaneous power provider. Although the supercharger has its strong point it also has it;s weak points. Since a supercharger uses a crankshaft to power the turbine. This can use up to 21% of the engines power to spin. In most cases a supercharge supplies up to 46% of the engines power. Supercharger can also add strain to the engine in other places damaging weak engines. The increase in total power can be up to 100% making the supercharger very effective for adding power.
Turbochargers produce boost in a slightly different way than does a supercharger. A turbo charger is a smaller, lighter and more efficient way to produce boost. It is attached to the exhaust manifold, the turbo has a turbine which is power by the flow of exhaust from the engine. When the turbine is spun it compresses the air through the intercooler and into the intake manifold producing boost. The turbo is a more efficient way to use forced induction in that little or no power is taken from the engine. Most turbos run around 6 to 8 pounds per square inch, at sea level air pressure is 14.7 psi, this is almost a fifty percent increase in air that is packed inside the cylinders. So it's almost the same concept as the supercharge but instead of stealing power from the crank it uses the produced exhaust gases to it's advantage. Some choose to run their turbos at 15-25 psi this increase is great and things really start to heat up so the air molecules will need to be cooled even more than before or the turbo would become almost ineffective.
Turbo's and superchargers have a turbine the action of which heats the oxygen. When the air is pressurized and forced into the intake it is heated which results in a smaller, less dense air mass. When air is less dense there is less air in a space than can actually be put their. When oxygen atoms become "excited" they consume more space than when they are cold and slower moving. The intercooler is used to counter this effect. The intercooler sits in front of the radiator and very low to the ground because that is where the coldest air is.
When the air intake sucks the air in, it puts it right into the turbo then it goes through the intercooler and then on to the intake. The intercooler is an important part to the turbo system, only because it allows the engine to receive even more air because the air is condensed. When no intercooler used the air inside the intake manifold can reach temperatures well above 250 degrees, but when an intercooler is used the air is around 150 degrees. This affects the density of the oxygen which allows for a hotter burn and more power form the engine the the wheels. Other things such as oil that is ran through the turbo becomes hot because it is the same oil that an engine uses to lubricate itself. The same method can be used for oil, an oil cooler is much like an intercooler but it cools the oil down and it becomes thicker and cooler.
- Turbochargers Karim Nice, HowStuffWorks, 2010.
- Intercooler Theory John Estill, GNTTYPE, 2010.
- Turbo Vs. Supercharger Perfect Power, 2010.
- Gasoline Chris Kaiser,April 2001.
- Superchargers William Harris, HowStuffWorks, 2010.
- Forced Induction Maytas Varga, StreetRacersOnline, 2003.