rpm and horsepower can steadily build up to their maximum.  With a constant-speed propeller, the tachometer reading  should come up to within 40 rpm of the red line as soon as  full power is applied and remain there for the entire takeoff. Excessive manifold pressure raises the cylinder combustion  pressures, resulting in high stresses within the engine.  Excessive pressure also produces high-engine temperatures.  A combination of high manifold pressure and low rpm  can induce damaging detonation. In order to avoid these  situations, the following sequence should be followed when  making power changes. The turbocharged engine allows the pilot to maintain  sufficient cruise power at high altitudes where there is  less drag, which means faster true airspeeds and increased  range with fuel economy. At the same time, the powerplant  has flexibility and can be flown at a low altitude without  the increased fuel consumption of a turbine engine. When  attached to the standard powerplant, the turbocharger does  not take any horsepower from the engine to operate; it  is relatively simple mechanically, and some models can  pressurize the cabin as well. The cruise power charts in the AFM/POH should be  consulted when selecting cruise power settings. Whatever  the combinations of rpm and manifold pressure listed in  these charts—they have been flight tested and approved  by engineers for the respective airframe and engine  manufacturer. Therefore, if there are power settings, such as  2,100 rpm and 24 inches manifold pressure in the power chart,  they are approved for use. With a constant-speed propeller,  a power descent can be made without over-speeding the  engine. The system compensates for the increased airspeed  of the descent by increasing the propeller blade angles. If the  descent is too rapid or is being made from a high altitude,  the maximum blade angle limit of the blades is not sufficient  to hold the rpm constant. When this occurs, the rpm is  responsive to any change in throttle setting. The turbocharger is an exhaust-driven device that raises the  pressure and density of the induction air delivered to the  engine. It consists of two separate components: a compressor  and a turbine connected by a common shaft. The compressor  supplies pressurized air to the engine for high-altitude  operation. The compressor and its housing are between the  ambient air intake and the induction air manifold. The turbine  and its housing are part of the exhaust system and utilize the  flow of exhaust gases to drive the compressor.  [Figure 11-9] Although the governor responds quickly to any change in  throttle setting, a sudden and large increase in the throttle  setting causes a momentary over-speeding of the engine  until the blades become adjusted to absorb the increased  power. If an emergency demanding full power should arise  during approach, the sudden advancing of the throttle causes  momentary over-speeding of the engine beyond the rpm for  which the governor is adjusted. The turbine has the capability of producing manifold pressure  in excess of the maximum allowable for the particular engine.  In order not to exceed the maximum allowable manifold  pressure, a bypass or waste gate is used so that some of the  exhaust is diverted overboard before it passes through the  turbine. Some important points to remember concerning constant- speed propeller operation are: The position of the waste gate regulates the output of the  turbine and therefore, the compressed air available to the  engine. When the waste gate is closed, all of the exhaust  gases pass through and drive the turbine. As the waste gate  opens, some of the exhaust gases are routed around the  turbine through the exhaust bypass and overboard through  the exhaust pipe. 11-8 • The red line on the tachometer not only indicates  maximum allowable rpm; it also indicates the rpm  required to obtain the engine’s rated horsepower. • A momentary propeller overspeed may occur when  the throttle is advanced rapidly for takeoff. This is  usually not serious if the rated rpm is not exceeded  by 10 percent for more than 3 seconds. • When increasing power, increase the rpm first and  then the manifold pressure • When decreasing power, decrease the manifold  pressure first and then decrease the rpm • The green arc on the tachometer indicates the normal  operating range. When developing power in this range,  the engine drives the propeller. Below the green arc,  however, it is usually the windmilling propeller that  powers the engine. Prolonged operation below the  green arc can be detrimental to the engine. • On takeoffs from low elevation airports, the manifold  pressure in inches of mercury may exceed the rpm.  This is normal in most cases, but the pilot should  always consult the AFM/POH for limitations. • All power changes should be made smoothly and  slowly to avoid over-boosting and/or over-speeding. Turbocharging