How to Explain a Turbo Engineby Don Bowman
Turbos are used on many late-model vehicles to enhance the performance of small displacement engines---usually four-cylinder engines. The small displacement engines have advantages in low fuel consumption, although they fall deficient, in most cases, in the power department. A turbo engine has higher horsepower, but does not sacrifice fuel economy, especially if the vehicle is driven normally (without putting your foot in it everywhere you go).
Explain how a normally aspirated engine operates where the intake of fuel is concerned. A normally aspirated engine relies on engine-produced vacuum for the induction of air, which is always subject to atmospheric pressure. As atmospheric pressure continuously changes, the air induction in terms of cubic feet per minute (CFM) changes as does the horsepower for a given pressure. Hot, moist air is thin with a resulting reduction in horsepower; whereas a cold, dry air has a corresponding increase in horsepower. The cubic-inch displacement of an engine is the volume of air and gas within the cylinder.
Explain the effect of turbocharging an engine. By turbocharging, the engine, when the turbocharger is working, no longer relies on a vacuum to draw air into the engine. The engine normally relies on atmospheric pressure over vacuum to charge the cylinder with air and fuel. As the temperature and humidity change, the air charge either increases or decreases, and the computer uses sensors to add the right amount of fuel under the specific atmospheric conditions for the proper mixture. When the turbocharger is working, it is taking in air, compressing the air and forcing it into the intake manifold at pressure far in excess of atmospheric. This process, in essence, is effectively increasing the cubic-inch displacement of the engine since it is forcing more charge into the cylinders than normal atmospheric pressure would permit. This "Forced Air Induction" has a resultant 30 to 50 percent or more horsepower gain.
Explain how the turbo works. The turbo is a mechanical device that resembles a snail shell with a plate through the center separating the two halves. A set of impeller blades is located in each side, connected by a shaft running through the center. Both impellers turn simultaneously. The most significant element of a turbo is that the pressure of the exhaust gases exiting the engine powers it. The exhaust gasses spin the turbo blades on one side, while this power is transmitted to the air charge side. As the exhaust spins the exhaust side, the intake charge side draws air into the turbo at high speed and compresses it. The now compressed air travels through a pipe to an intercooler, which is a separate radiator that cools the air and makes it denser. The air then travels from the intercooler to the intake manifold through another pipe with a tight seal to the intake manifold.
Explain the performance aspect and operational conditions. The turbo is free horsepower, unlike other charging systems. A turbo is dormant during most normal driving conditions. It must be spun to an average of 3,000 rpm before it builds horsepower. This gives power in accelerating where needed. The upside is that the turbo takes no horsepower or fuel to operate it and, in normal cruise, does not affect fuel economy. The only downside for performance enthusiasts is that it has turbo lag whereas a supercharger has no lag. A turbo charger is the best suited for motor vehicles under normal use since it requires little to no maintenance.