ZOSicK
May 14th, 2005, 12:30 PM
A turbocharger uses a turbine that is driven by the hot, expanding exhaust system stream to power a centrifugal compressor which forces air into the engine. Because a turbo is actually driven by wasted energy, there is no loss from the engine to power the turbo. However, because the system is run off the exhaust, it may take some time before the exhaust level builds up to a sufficient level to run the turbo charger. This delay in power delivery is called "Turbo Lag" and can lead to a significant pause between stepping on the gas and the feel of additional power. Furthermore, turbos often require cool down periods after use (meaning you have to let the car idle for a few minutes (!) everytime you want to shut the engine off, or else reduce the life of your turbo-charger, which only last 7-10 years anyway. More modern turbo charger designs have allowed turbos to slowly spin down even after the engine has been shut off and are more durable than older designs.
Most turbos use intercoolers, wastegates and compressor bypass valves (blow off valves) to help provide more useable power. An intercooler is a heat exchanger that is used to cool the air heated by the turbocharger's compressor. Therefore, the intercooler can significantly boost power because the cooler air it provides is more dense than the hot air straight out of the turbo. An intercooler also takes thermal load off of the engine by cooling the intake air. A wastegate is designed to regulate boost pressure, and is simply a valve in the exhaust system that allows some of the exhaust to bypass the the turbo when it is not needed. The Bypass valve is a valve between the throttle and the turbo that vents extra boost pressure. When this valve vents to the outside air, it is called a blow off valve, and when it vents back into the inlet of the turbo, it is called a compressor bypass valve.
A turbocharged engine's compression ratio must be lowered by using a lower compression piston, since an excessive amount of pressure will wear on the piston, connecting rods, and crankshaft, and destroy the engine. All of these parts then, as well as the transmission, must be strengthened on a turbocharged engine or it will be torn apart by the increased horsepower.
Advantages: Greater peak power
Disadvantages: Lag in power delivery, long-term durability, cold-start emissions
Applications: Recommended for high RPM applications (i.e. I4s)
Most turbos use intercoolers, wastegates and compressor bypass valves (blow off valves) to help provide more useable power. An intercooler is a heat exchanger that is used to cool the air heated by the turbocharger's compressor. Therefore, the intercooler can significantly boost power because the cooler air it provides is more dense than the hot air straight out of the turbo. An intercooler also takes thermal load off of the engine by cooling the intake air. A wastegate is designed to regulate boost pressure, and is simply a valve in the exhaust system that allows some of the exhaust to bypass the the turbo when it is not needed. The Bypass valve is a valve between the throttle and the turbo that vents extra boost pressure. When this valve vents to the outside air, it is called a blow off valve, and when it vents back into the inlet of the turbo, it is called a compressor bypass valve.
A turbocharged engine's compression ratio must be lowered by using a lower compression piston, since an excessive amount of pressure will wear on the piston, connecting rods, and crankshaft, and destroy the engine. All of these parts then, as well as the transmission, must be strengthened on a turbocharged engine or it will be torn apart by the increased horsepower.
Advantages: Greater peak power
Disadvantages: Lag in power delivery, long-term durability, cold-start emissions
Applications: Recommended for high RPM applications (i.e. I4s)