Camshaft Design

The camshaft is at the heart of an engine's functional ability. The Rover V8 utilises a single, central camshaft that does not have the ability to alter its timing once installed. This means that the characteristics of the engine can only be altered at design time or by re-timing a camshaft that is already fitted. The result of this is that the initial choice and design of a camshaft is of the greatest importance. V8Developments produce a number of 'stock' camshafts which are particularly suited to individual applications but also provide a camshaft design service to allow for specific needs and uses. In order to 'design' a camshaft we need as much information as possible regarding the engine itself (unless we are building it, of course). The design process is a bit of a 'Dark Art' and to be honest it would be pointless to go through every step in extreme detail; suffice to say that a camshaft can make a huge difference to performance of an engine and the following attributes are what give the cam' its characteristics.

  • Lift
  • Duration
Stage II exhaust port

As a camshaft rotates the lobe of the cam, which is in contact with a follower, produces an increasing amount of 'lift' until it reaches its peak and begins to reduce back to its closure point. This lift directly translates into the distance that the cylinder valve is 'lifted' from its seat. Theoretically the higher the lift the more fuel / air mixture can be drawn into the cylinder... but there are limitations! The crankshaft and camshaft (in a Rover V8) are directly connected by the timing chain, inside the front cover. This means that there is a limit to how far the valve can move without hitting the piston. This distance is also dependant on the 'duration' that the valve stays open as if the valve is already partly closed when the piston reaches its highest point then the maximum opening distance can actually exceed the clearance between the pistons highest and valves lowest position. This needs to be carefully calculated prior to building the engine.

Cam lobe diagram

This is, in its simplest description, the time that the valve is in an open position. As the camshaft turns and causes the lifter to rise the valve is depressed by the rocker arm and the valve 'opens' allowing air / fuel into the cylinder. Durations are normally quoted in degrees of rotation rather than actual time and there is normally a reference point or minimal measurable lift (normally 0.050" or 0.016" depending on manufacturer). This, therefore, means that a camshaft that quotes a duration of 268 degrees at 0.050" lift will show an open position for 268 degrees of rotation (of the crankshaft). This information is crucial for us as engine builders. This is shown on the diagram above as the rotational degrees between points A and B.

As discussed further in the camshaft timing section, a combination of these values and a little calculating can tell us the ideal position in which to position the camshaft (within the 360 degree circular motion) in order to have the camshaft opening and closing the vales as effectively as possible.

There is also a need to consider the application of the engine. In a vehicle where high rpm is likely to be maintained for long periods (as seen in circuit racers) the camshaft will be designed to place the maximum air flow into the cylinder at higher rpm than say for an automatic Range Rover which will probably struggle to rev higher than 5,500 rpm its whole life. Camshafts are therefore often referred to as 'High Torque' or 'High Rpm' cams in order to give some definition to their designation. The higher rpm that a camshaft is designed to work at, the worse the low rpm performance will be (within some boundaries of course) and this is the reason that cams referred to 'Race' will produce a particularly poor idle and it will be difficult to drive the car at low engine speeds. High torque camshafts, however, will produce a particularly smooth idle and easy low rpm running but will 'run out of puff' before high rpm is ever seen.

When push comes to shove we end up trying to create a 'best of both' approach for road cars so that they are drivable but also produce reasonable performance at high rpm ... and here is where the magic is needed! We have spent a quite obscene amount of time and testing to produce a range of camshafts that we (and it must be said, the vast majority of our customers) are happy with at both ends of the scale. We do of course have camshafts ground to individual specifications from time to time but the range shown on the products pages cover most 'normal' eventualities.