Timing Components: Description and Operation

Timing drive mechanism







Camshafts with cylinder-specific cam contours

The intake and outlet camshafts for both engines have a basic circle diameter of -> length: 38 mm. The intake valve lift is -> length: 3.6 mm and -> length: 11 mm. The outlet valve lift on cylinders 1, 2, 6 and 8 is -> length: 8 mm, while the outlet valve lift on cylinders 3, 4, 5 and 7 is -> length: 9.2 mm.

The engine design, with a V8 crankshaft and -> control value: 90° throw, guarantees superb mass and torque balancing. In this engine design and a design with normal cam contours (same cam strokes), individual cylinders would be hindered during emission into the exhaust manifold.

The reason for this is that the surge of exhaust gas that emerges during the early (sooner than normal) outlet-valve opening for the respective cylinder (e.g. cylinder 2) goes into the overlap period of the next cylinder (cylinder 3). This would have a detrimental effect on the charging of the cylinders. Too many residual exhaust gases would also have a negative effect on the knock limit.

The firing order of the Cayenne (1 - 3 - 7 - 2 - 6 - 5 - 4 - 8) would put cylinders 3, 4, 5 and 7 at a disadvantage in terms of volumetric efficiency. These cylinders therefore have a larger cam stroke. This means that the cylinders are charged evenly, which results in an optimised torque curve in the entire rev range.







The chain drive consists of a 3/8" -> length: 8 mm wide duplex bush chain, which drives the two intake and outlet camshafts.







The chain is guided by two specially coated guide rails. The lower guide rail on cylinder row 1 to 4 is also designed as a tensioning rail. The hydraulic chain tensioner is connected to the engine oil circuit and is totally maintenance-free.

Sprocket







The lower sprocket, which drives the timing chain and the chain for the oil pump, has a friction disk on the front (facing the pulley) and rear (facing the crankshaft) for improved torque transmission.