The New Engines
The new engines, code-names PE146 for the Rover 2300 and PE166 for the Rover 2600 are of an in-line six-cylinder configuration. The 2300 actual displacements 2350cc and 2597cc for the Rover 2600 engine. The six cylinder has important advantages with corresponding customer benefits, over the conventional four-cylinder engine featured by most major competitors.
The benefit of smooth quiet running derives from the two main advantages of the in-line six configuration over the more common in-line four.
- Torque delivery is smoother than the in-line four cylinder engine because successive power strokes overlap: this can be seen in the diagram below. The result is a smoother running engine, particularly at low speeds.
- The crankshaft assembly has better mechanical balance because force is delivered more evenly, at a greater number of points along its length. This reduces engine vibration and hence contributes to quiet running.
The benefit of quiet operation is also contributed to by the use of an overhead camshaft which permits the cams to operate more directly upon the cylinder valves, with fewer contributing parts. The more common system of locating the camshaft in the crankcase involves a series of pushrods to transmit the action of the cams to the rocker arms on the top of the cylinder heads.
The overhead camshaft system eliminates the need for a pushrod assembly, and provides a more direct and efficient system for operating the cylinder valves.
The camshaft is driven from the crankshaft by a toothed drive-belt instead of the more conven-tional chain. The belt is made of oil-resistant rubber moulded onto non-stretch cord, and an important advantage as far as servicing is con-cerned is its freedom from tensioning problems.
The drive belt is quieter during operation.
Although drive belts are not yet as commonly used as chains they have now been well proven in service by many engine manufacturers.
Viscous Coupling Fan
The cooling fan is another example of the thought taken all through the design stage to maximize on an efficient and quiet high-performance engine. Instead of being driven direct from the engine the fan is driven via a silicone fluid viscous drive. As a result, while the speed of the fan-and hence its efficiency — remains proportional to the speed of the engine, it does not have to run at full engine speed, One spin-off is of course economy as less engine power needs to be diverted to the fan.
Special Valve Operation
We have seen that the reduction of the number (and weight) of parts of the valve operating gear, by using a single overhead camshaft, contributes to the benefits of quieter operation. However, these particular benefits can often be in conflict with the requirements for a high-performance engine.
For example, you may know that high-performance engines sometimes utilize twin overhead camshafts. One advantage of this system is that it permits exhaust and inlet valves to be located opposite each other, instead of side by side (as in the example of the typical single overhead cam-shaft we discussed earlier on). The opposite location of exhaust and inlet valves — on either side of the cylinder head — ensures a good crossflow of gases and contributes to efficient combustion and hence to performance and economy.
However, twin overhead camshafts add to the number of parts and weight of the engine, opposite we examine how the new Rovers provide the performance features we have just discussed, using the single overhead camshaft and a special valve configuration similar to that used in the award-winning Dolomite Sprint cylinder head.
The solution to obtaining the performance benefits of opposite inlet and exhaust valves is explained and illustrated below:
Inlet valves are operated directly by cams and bucket tappets. Exhaust valves are operated via rocker arms activated by the inlet cams. In this way, each cam activates both an inlet valve (directly) and an exhaust valve (indirectly, via a rocker arm).
Classic cross-flow design
Using this special valve operation from a single camshaft permits the opposite location of inlet and exhaust valves. Here it has been possible to use a valve inclination of 40° included angle, which is the optimum angle for the modified hemispherical shape of the combustion chamber. This cross-flow design permits the mixture to enter the chamber easily, gives highly efficient combustion and free exhaustion of gases from the chamber.
To summaries then, the special cam con-figuration
1. Permits the two valves in each cylinder to be operated by the same cam. 2. Allows, therefore, inlet and exhaust valves to be located opposite each other, at the optimum angle, in the classic cross-flow design.
3. Gives highly efficient intake, combustion and exhaustion of gases.
Equally important to engine efficiency is the degree of control of the petrol/air mixture entering the combustion chamber.
As you know, a good carburation process depends on several factors apart from the refinement of the carburettor alone. Below we have pinpoined the main features which contribute to the new engines' efficient carburation from the initial air intake to the distribution of the petrol/air mixture to the cylinders.
- Air temperature control (ATC) and water-heated inlet manifold. The ATC draws in warm air from a shroud around the exhaust manifold. The inlet tracts are water heated by a steel pipe cast on the underside of the tracts. Both the ATC and the water-heating are thermostatically controlled to provide the optimum temperature for the air reaching the carburettors. The resulting benefits are quicker warm-up and good economy.
- Long inlet tracts which have the 'ram' effect of accelerating the air flow. This permits a greater, more constant petrol/air mixture to be drawn into the carburettors and improves torque.
- Capstat, gives an automatic mixture control which varies the mixture in response to the warm-up of the engine. The results are controlled exhaust emission levels and good fuel economy.
- Twin SU HS 6 carburettors for better control and distribution of the mixture, giving efficient combustion and good performance.
Twin Exhaust Outlets from the Manifold.