Variable Induction System: Description and Operation
VARIORAM INTAKE SYSTEMTo achieve high engine output and increased torque in the middle rpm range, the 911 Carrera is fitted with a timed tuning flap and variable-length intake pipes.
Tuning of the intake pipes is based on the principle of effective length tuning.
Each individual intake pipe is made up of two sections. One section is bolted rigidly to the cylinder head while the other section slides in or out to double the overall intake pipe length.
For this purpose, the engine is fitted with one vacuum controlled slide per cylinder bank. The slides are actuated by solenoids that are connected to vacuum by a solenoid switching valve.
A = Pulse pipe charging with long intake pipes
B = Tuned-intake pressure charging with short intake pipes (Tuning flap closed)
C = Tuned-intake pressure charging with short intake pipes (Tuning flap open)
A - Pulse pipe charging
When the pipe gap (5) between the slide (4) and the central intake rail (6) is closed, the single-chamber system, i.e. the pulse-pipe supercharging system, is activated. The intake air now flows from the central intake rail across torque-optimized pulse pipes (intake pipes) into the cylinders.
B - Tuned-intake pressure charging
When opening the slides (4) to switch from pulse pipe charging to tuned-intake pressure charging, the intake air flow is separated into individual flows in the intake section downstream of the air mass sensor (1).
This branch system is connected both to the central intake rail (6) of the single-chamber system and to the tuned-intake system (7) located beneath.
From the central intake rail, part of the intake air flows across the intake pipe extensions designed as tuning pipes directly into the intake stacks of the short vibration pipes and then to the individual cylinders that are in the intake stroke at that particular moment (2). Most of the intake air passes the second throttle valve (2) to enter the first large tuning pipe of the tuned-intake pressure charging system (7) to the resonance chambers. In this process, the air mass flowing to the short vibration pipes is optimized by the tuned-intake pressure charging system.
C - Tuned-intake pressure charging with open tuning flap
The tuning flap (3) is located in the second large tuning pipe. The tuning flap is closed initially but is opened from a certain engine speed, causing the flow cross- sectional area between the resonance chambers to be increased. Air can now flow into the resonance chambers across all connecting pipes.
Switching conditions of the intake pipe extensions and the tuning flap
1. When the ignition is switched on, the DME control module triggers the solenoid valves. When the engine is started, both the intake pipe extensions and the tuning flap are actuated. As soon as the idle rpm is reached, the signal to the solenoids is interrupted and both the intake pipe extensions and the tuning flap now assume their home positions.
2. When reaching an engine speed of 4,840 rpm and a throttle opening angle of at least 50°, the DME control module feeds an electrical signal to the solenoids of the intake pipe extensions, causing the extensions to be actuated. The intake system now switches from pulse pipe charging to tuned-intake pressure charging.
3. When an engine speed of 5,840 rpm is reached and when the throttle is opened by more than 50°, the DME control module opens the tuning flap and thus increases the tuning pipe cross-sectional area.
4. At an engine speed of 6,640 rpm, the tuning flap is closed again.