Fuel & Ignition System

VarioCam Plus

The new 911 Turbo (997) is provided with the latest development version of the variable valve control VarioCam Plus with continuous adjustment of the intake camshafts and valve lift switching of the intake valves. This system permits optimization of engine output and torque on the one hand and, on the other, also makes it possible to reduce fuel consumption and exhaust emissions while improving running smoothness.

Both individual systems of the VarioCam Plus (camshaft adjustment and valve lift switchover) are controlled by the Motronic control unit ME7.8.1. This control unit has been designed specifically for these requirements with a high processor capacity. This is necessary because the input values for "engine speed", "accelerator pedal position", "engine oil and water temperature" as well as gear speed detection are required to control VarioCam Plus. The demand for torque or power is compared with the stored program maps. A decision on how VarioCam Plus must react is made in milliseconds.

Camshaft Adjustment Of The Intake Camshafts







The 911 Turbo (997) features continuous adjustment of the intake camshafts by vane adjusters. The load and speed dependent adjustment range of the intake camshafts is 0 to 40° crankshaft angle.

Valve Lift Switching Of The Intake Camshafts

The small valve lift was increased from 3.0 mm (996) to 3.6 mm in order to make more efficient use of the advantages of VarioCam Plus with continuous camshaft adjustment and a larger adjustment range with respect to consumption, output and exhaust emissions. The valve lift adjustment system consists of switchable flat-base tappets on the intake side of the engine which are operated by means of an electrohydraulic 3/2-way switching valve.

Since there are two different cam forms on the intake camshaft, the corresponding valve lift curves act on the engine when the respective cams are switched. The flat-based tappets consist of two nested tappets which can be locked against each other by way of a pin. The inner tappet is in contact with the small cam and the outer tappet with the large cam. A hydraulic compensating element for the valve clearance is always integrated in the power flow of the tappet.

Cold Start

VarioCam Plus already significantly improves cold starting of the engine, and also allows emissions to be reduced during the warming-up phase.

Idle Speed

The engine is operated with the small intake cam (3.6 mm) at idle speed. Optimum timing is guaranteed thanks to fully variable camshaft adjustment. The small valve lift permits a reduction in fictional loss, a significantly increased charge movement thanks to the extremely short opening times, as well as lower emissions from previous combustions in the combustion chamber. This results in consumption and emission reductions of up to 10 % at the same time as significantly improved idling quality.

Partial Load

Operation with internal exhaust gas recirculation is optimum under partial load conditions for the purpose of dethrottling and in order to reduce the engine consumption. For this purpose, the camshaft phasing for the small valve lift is adjusted in order to achieve a large overlap, therefore allowing a large proportion of time for exhaust recirculation.

Full Load

In full-load operation, a high torque and high maximum output are achieved on the one hand through a low-loss charge cycle and, on the other, by an uncompromising cam contour design with a maximum valve lift of ten millimeters and correspondingly adapted opening and closing times of the valve strokes.