Intake Manifold: Description and Operation
Expansion Intake Manifold
The 911 Turbo DFI features an expansion intake manifold. The exceptional operating principle of this unique system, used for the first time in the 911 GT2 (997), also improves engine efficiency in the new 911 Turbo. This results in higher engine power as well as lower fuel consumption at high loads and engine speeds.
The operating principle of the expansion intake manifold is based on a specific use of the air oscillations in the intake manifold. This involves expansion and therefore cooling of the turbocharged air when it flows into the combustion chambers. At high loads and engine speeds in particular, ignition performance of the fuel-air mixture is optimized by way of the cooler air, thereby increasing engine efficiency. This effect is achieved through the unique geometry of the overall system. Short intake pipes and a long air distributor tube with a small diameter are characteristic features of the expansion intake manifold. The system was developed for the new 911 Turbo on the basis of the expansion intake manifold of the 911 GT2 (997). The physical principle has been utilized even more intensively with additional cooling of the charge air through expansion and the system's geometric dimensions have been adapted correspondingly.
The functional advantage of the expansion intake manifold can best be seen in a geometrical comparison of the intake manifold air distributor tube. In the previous model with 480 hp, the distributor tube had an internal diameter of 85 mm and a length of 270 mm. In the new 500 hp 911 Turbo, the distributor tube is 440 mm long and has an internal diameter of only 50 mm. Despite a reduction in the flow cross-section of the distributor tube by more than 65 %, approx. 4 % more power has been achieved with the new expansion intake manifold.
Expansion intake manifold made of plastic with silver-colored textured paint finish. Additional cooling of the charge air through expansion effect when air flows out of distributor tube "EX - Expansion point". Long air distributor tube (440 mm) with small internal diameter (50 mm) downstream of the electronic throttle, then short, wide intake pipes.
Pressure Sensor (With Integrated Temperature Sensor)
In the new 911 Turbo, a pressure sensor installed on the right intake manifold detects the air flow (load detection), which is also used as a basis for determining the required fuel injection quantity. Compared with the hot-film mass air flow sensor (MAF sensor - downstream of the air filter) used in the previous model and the current 911 Carrera models, load detection via a pressure sensor offers lower flow losses.
Advantages of the pressure sensor:
- Increased performance thanks to dethrottling of the intake section
- Higher precision for small air flows
- High resistance to soiling
- Lightweight design (the pressure sensor replaces 2 MAF sensors)
- (in the past, 2 hot-film mass air flow sensors were installed between the air filter housing and electronic throttle)
In order to ensure that the correct mixture composition is always present in the combustion chambers, the actual intake air mass is continuously calculated in the DME control unit by way of the pressure sensor signal. As a result, the correct mixture is always available in the combustion chambers, and any changes in the atmospheric pressure (due to changes in altitude) and outside temperature are compensated. This new pressure sensor replaces the hot-film mass air flow measurement system used in the past and also contributes to increased performance by dethrottling the intake section.
Intake Air Temperature Sensor
The integrated temperature sensor is used to measure the intake air temperature. The load signal of the pressure sensor and the intake air temperature can be found under the DME actual values.
Voltage characteristic of the pressure sensor as a function of intake manifold pressure:
Supply voltage = 5 Volt
Uout - Output voltage (V)
US - Pabs - Absolute pressure (kPa)
The voltage characteristic as a function of the intake manifold pressure. The plausibility check for the pressure sensor signal is performed in the DME control unit. For this purpose, the current filtered values of the ambient pressure sensor (in the DME control unit) as well as the intake manifold pressure sensor and boost pressure sensor upstream of the throttle valve are compared with each other after "Ignition On" > 10 seconds or control unit run-on > 10 seconds.