Development of the non-turbocharged Rolls-Royce V8 Engine 1959-98: illustrated with engines in the basement of The Hunt House
by David Towers
The Rolls-Royce Silver Cloud & Bentley S were introduced in April 1955 with the 4.9 litre 6 cylinder engine. Rolls-Royce realised this was the ‘end of the line’ for the engine, which had started life in 1922 in the Rolls-Royce 20hp.
Cars were getting larger, heavier and customers wanted better performance. This required more power. This could be achieved with a higher revving engine, but it would not satisfy the Rolls-Royce qualities of relaxed performance. A larger capacity engine was required, ideally more compact than the existing straight ‘6’. The US showed the way with their V8 engines – more capacity in a smaller (but wider) space. Also, V8 engines tend to have good low speed torque, but not exceptional power – what Rolls-Royce wanted. (6 & V12 engines tend to have high speed power but less low speed torque).
Jack Phillips, the designer of the V8, was summoned into Harry Grylls (Gry) office in 1954. Gry said ‘our car engine is running out of steam. Go away and think around a 50% increase in power and torque.’
A V6 wouldn’t be sufficiently smooth, and would have too large cylinders. A flat 8 would be too wide, and restrict steering lock. So Jack Phillips suggested a V8. Jack found to his chagrin that Gry had already asked Derby’s Advanced Project Design Office to look at a V8. The first engine was the L380W (above) with a 3.8 inch bore x 3.5 inch stroke and 5,203cc capacity. This was first tested in an experimental Silver Cloud 30-B in April 1956.
The picture shows it has a hemispherical combustion chamber with a central sparking plug. It has a single Carter downdraft carburettor. In the engine designation ‘L’ means V8; ‘380’ is the bore of the engine (3.8 inches - the cylinder's diameter); ‘W’ means Wide. The first engines had a 3.5 inch stroke (the amount the piston goes up and down). At the time, hemispherical combustion chambers were popular (e.g. the Jaguar 3.4 litre twin overhead cam engine introduced in the XK120 in 1948). They give good breathing and high power. This arrangement was not proceeded with. It was heavier than predicted with slow flame propagation in the combustion chamber and an engine which was a very tight fit in the narrow Silver Cloud engine bay (which was designed for the 4.9 litre 6 cylinder engine).
The road testers described the engine as ‘the gutless wonder’, but its acceleration down Pyms Lane (in front of the factory) was better than the old 4.9 litre Six. The V8 was much smoother than the six, and its gentility was mistaken for a lack of power.
This engine was replaced by the L380N (N=narrow) engine with overhead valves and the sparking plug on the side. The L380N had the same bore and stroke as the L380W. It was probably the same as the L380W but with a different cylinder head (& pistons). This engine was 7 inches narrower than the L380W, thus making it a less tight fit in the Silver Cloud engine bay. And, it was significantly lighter than the L380W engine.
The final production engine was the L410, with a 4.1 inch bore and a slightly longer 3.6 inch stroke. This gave a capacity of 6,230cc. There was no change to the engine block compared with the 5.2 litre L380N engine, as the block was sufficiently large to accommodate the larger dimensions. It was introduced in September 1959 in the Rolls-Royce Silver Cloud II, Bentley S2 & Rolls-Royce Phantom V.
Why did Rolls-Royce ‘drop’ the 5,203cc engine and end up with the 6,230cc engine? The 5.2 litre engine is only 10.6% larger than the 4.9 litre straight 6. This would limit future development. The final 6.23 litre V8 was 27.5% larger than the ‘old’ straight 6, giving much more scope for future development. Another advantage of the larger engine was that a 27.5% increase in engine capacity would give a similar increase in low speed torque. This would allow higher gearing and ‘waftier’ progress in the car (the Silver Cloud II’s gearing was 11.2% higher than the Silver Cloud I).
The first V8 engine in the Silver Cloud II had two 1¾ inch SU carburettors, compared with two 2 inch units on the 4.9 litre Six. It is clear that the V8 was quite restricted on the air inlet side, with 76.5% of the carburettor intake area compared with the Six, but with a 25% increase in capacity. The sparking plugs were placed under the exhaust manifold (see picture on page 1), for a 24,000 mile life (for the USA). Removal of the sparking plugs required removal of the front wheel and a panel between the wheel arch and engine.
One of the changes with the 1962 Rolls-Royce Silver Cloud III and Bentley S3 was an increase of the carburettor size to two 2 inch SU’s.
Silver Shadow 1965-77
The Silver Shadow was introduced in 1965. It was very different from the Silver Cloud. The Shadow had a unitary construction body, independent self-levelling rear suspension and disc brakes. Although it was shorter than the Silver Cloud III, it had more room inside. Very little was taken over from the Silver Cloud, except the engine and automatic gearbox.
The main change to the engine was moving the position of the sparking plugs to above the exhaust manifold, which made them easier to remove at a service. It remained with two 2 inch SU carburettors. There were significant (minor) changes to the engine to improve its emissions, so they could meet the regulations in all markets. This tended to reduce engine power. So, to compensate for this, in 1970 the engine capacity was increased to 6,750cc by increasing the stroke to 3.9 inch (from 3.6 inch, the bore remained at 4.1 inches). The increase in engine capacity is 8.3%.
Silver Shadow II 1977-80
The Rolls-Royce Silver Shadow II & Bentley T2 were introduced in April 1977. The major changes were the introduction of rack & pinion steering and automatic air conditioning. On the engine, the two SU carburettors were reduced to 1 7/8 inch. To partly compensate for the smaller carburettors, a twin pipe exhaust system was installed.
At the end of the production run in 1980, a fuel injected engine was introduced for the Californian market (& some others). This had a Bosch K Jectronic mechanical fuel injection. This engine continued (for the US) in the Silver Spirit.
Silver Spirit – Carburettors – 1980-86
The Rolls-Royce Silver Spirit was introduced in October 1980. The main changes were the new rear suspension, mineral oil hydraulics (instead of brake fluid) and a new body. The Silver Shadow II engine continued, essentially unchanged, with the 1 7/8 inch SU carburettors. (note: from this point, I will just refer to ‘model years’ – the 1987 model year stretched from August 1986 to August 1987, with the change usually in the factory’s annual August holiday).
Silver Spirit – Mechanical Fuel Injection –1987-93
For the 1987 model year, Rolls-Royce introduced fuel injection on all 4 door models. The engines looked somewhat different from the earlier fuel injected Shadow II engine, but essentially there was no difference.
The mechanical fuel injected cars looked similar to the engine above, although there was an attractive cast aluminium inlet pipe to the centre of the engine. There were very minor changes to the engine when the Silver Spirit II was introduced in 1990 model year, such as the change to M Jectronic fuel injection (essentially the K Jectronic system with an electronic ‘tweak’). Production of the Silver Spirit II (& equivalent models) ceased in Summer 1993, just before the introduction of the RR Silver Spirit III (for 1994 model year).
Developments – Silver Spirit II to Silver Spirit III
In the Hunt House basement, there are some interesting V8 development engines, which lie between the Silver Spirit II and Silver Spirit III engines. Most are designed to improve 'breathing’. This increases the power of the engine, and, to a lesser extent, its efficiency.
Better breathing with mechanical fuel injection This engine has mechanical fuel injection (like the Silver Spirit II). The throttle body is at the front of the picture. The intake air goes upwards to the plenum chamber (with Rolls-Royce name on top), from which there are eight pipes, one to each cylinder.
This is an interesting twin overhead camshaft engine with electronic fuel injection. In fact, it has four overhead camshafts, two above each ‘V’. The sparking plugs are between the camshafts, much more accessible than in the existing V8 engine. A twin overhead camshaft and central sparking plug would indicate a hemispherical combustion chamber, like the original L380W engine. You can see a 4 sparking plug distributor at the end of the inlet camshaft (there’s no space in a Silver Spirit engine bay for this!). The inlet manifold has a pipe to each cylinder, but the single air intake (the two elliptical holes) looks very restrictive. With no central camshaft, it is not possible to have the hydraulic pumps (for the suspension & brakes) in the centre of the ‘V’. So, there are two separate hydraulic pumps driven from the crankshaft by the fan belt. Rumour suggests that this engine has a smaller capacity than the 6.75 litre V8 (e.g. around 5 litres), and probably four valves per cylinder. But it is said to produce as much or even more power (at higher revs) than the 6.75 litre engine. The drive from the crankshaft to the four camshafts would be by either a toothed belt or chain. I feel this is more likely to be a toothed belt. However, Rolls-Royce tradition was against chains (too much noise and reliability problems), with even more concerns over the reliability of toothed belts. A higher revving engine would give less relaxed cruising, but a smaller capacity engine would give better fuel consumption (less friction).
This early prototype Silver Spirit III engine is almost identical to the final production version. The view is from the back of the engine looking forward. The only significant difference is the plain plenum chambers on either side (rather than having the Rolls-Royce or Bentley name). The intake air comes from the air cleaner in the front offside wing, and then down the middle of the engine. The horizontal tubular item in the middle is the electronic idle bypass. Closest to the camera, the central pipe divides into two, to the left and right. Immediately after this bifurcation, there are two throttle butterflies, one for each bank of cylinders. The air on each side turns a right angle and forwards into each plenum chamber. From the plenum chamber, there are four pipes, one to each cylinder (2 plenum chambers x 4 pipes = 8 cylinders). Two of the pipes go to the cylinders below the plenum chamber and two to the opposite bank of cylinders. On either side of the engine between the plenum chambers, inside the V, are four square blocks on either side. These are the individual coils for each cylinder, and lead to the sparking plugs (on the outside of the engine). The leads go from these coils, under the plenum chamber and to the sparking plugs on the outside of the engine.
This is the final Silver Spirit III engine, looking from the front, but with some parts missing! These is no central air intake pipe and coils for the cylinders on the left hand side. However, it shows the individual intake pipes from the plenum chamber to each cylinder. You can see the two end pipes go to the cylinder below the plenum chamber the two middle ones to the opposite bank of cylinders. This allows an even ‘sucking’ from each plenum chamber. You can see that there is a complex set of pipes in the centre of the V. The ‘real’ engine will contain a central air intake pipe, the four coils above each bank and fuel injectors for each cylinder. All very complex! Over this ‘mess’ is a cover which makes it look tidy, but underneath, it isn’t!
For the post 1996 Bentley Turbos, in the middle of the ‘V’, and part of the air intake pipe, there’s a water to air heat exchanger to cool the compressed air from the turbocharger. Even more complex! The Silver Spirit III engines are more vulnerable to cylinder head gasket failures, and dis-assembling all these pipes before reaching the cylinder heads is both complex, time consuming and ‘labour’ expensive! The mechanical fuel injected engines are so much easier to repair, when replacing the cylinder head gaskets – and these engines are more reliable in this respect!
Exhaust gas catalysts were available before the Silver Spirit III, but they became standard when the Silver Spirit III was introduced in the 1994 model year (ie late 1993).
Power of Normally Aspirated Engines
For many years, Rolls-Royce were very reluctant to disclose the power of their engines, describing it as ‘sufficient’. It only became common knowledge when the turbocharged engine was introduced in the Bentley Mulsanne Turbo in Spring 1982. The power of this engine was stated as 50% more than the normally aspirated engine. And, compulsory disclosure in Germany gave the turbo’s power as 300bhp. So, the normally aspirated engine’s power was about 200bhp. The 200bhp can be taken as the engine’s power from its introduction in 1959 until fuel injection was introduced in 1987 model year. There was some variation, as meeting emissions regulations sapped power, but the increase from 6.23 to 6.75 litres restored much of the loss.
The engines with mechanical fuel injection were more powerful. The Autocar magazine tends to be the most reliable source. It gives 226bhp at 4.300rpm and 340lb ft torque at 1,500rpm for the RR Silver Spirit II in 1990. The power is higher for the 1994 (& later) Silver Spirit III engines with their improved breathing and more precise electronic fuel injection. The ‘agreed’ figure is 240bhp. There were some minor changes in 1996 model year, which said that Rolls-Royce had increased the engine’s power. However, this was contradicted (by RR) when the ‘light pressure turbo’ (LPT) engine was introduced in 1997 model year. Rolls-Royce said this engine produced 300bhp, and increase of 25% over the normally aspirated engine. 240bhp + 25% = 300bhp. On acceleration, for the pre-Silver Spirit III cars, 0- 60mph was 10-11 seconds. For carburettor cars, the maximum speed was just under 120mph. The mechanical fuel injected cars, with more power and higher gearing had a maximum speed of 126mph (mean). The Silver Spirit III cars are both quicker on acceleration and have a higher maximum speed. However, there is no reliable road test of these cars. Rolls-Royce claimed 0-60mph acceleration of about 9.3 seconds and a top speed of 133mph. However, RR’s figures tend to be ‘better’ than contemporary road tests. But, 0-60mph in under 10secs seems possible as is a maximum speed of over 130mph. The Silver Spirit was effectively discontinued in 1996 model year. However, six Silver Spirits were produced in 1997 model year. From 1997 model year, the Bentley Brooklands and Rolls-Royce Silver Spur gained the low pressure turbine (LPT) engine, so the only model then non-turbo was the Rolls-Royce Silver Dawn. The last Silver Dawn, and thus the last non-turbo car, was WCH66305 in 1998 model year (only 11 Silver Dawns were produced that year).
The V8 engine of 1959 has survived 50 years by the introduction of turbocharging in 1982.
Summary and Conclusion
At its introduction in 1959, the Rolls-Royce V8 was both an advanced and a conservative engine. Its most advanced feature was construction in aluminium, with ‘wet’ cast iron cylinder liners. As a V8 engine, it was very compact. It was a very large engine (in capacity), with quite conservative maximum revs (4,500rpm) and low power output per litre. The engine’s power output (per litre) never reached the 4.9 litre Six of 1959 (35.5 bhp/litre for the last (Spirit III) V8 verses 36.4 bhp/litre for the Six). Using a single camshaft with pushrods was conservative in 1959. Fifty years later, most engines have twin overhead camshafts. Until the Spirit III, it had restricted breathing, and there continued to be the limit of only two valves per cylinder (one inlet & one exhaust). The engine has always given excellent low speed torque. The combustion chamber shape is excellent for emissions and has allowed the engine to continue in production with much stricter regulations. When the BMW engines were installed in the RR Seraph/Bentley Arnage in 1998, it was said that the engine would not meet future emissions, but it continues to be used in 2009 (and further into the future with the Arnage replacement in 2010). The strength of the engine is demonstrated by the current Bentley Brooklands where it produces 520bhp – 60% more power than the original engine.
To me, it is disappointing that the engine didn’t produce significantly more power until introduction of the turbo in 1982. In 1959, the Rolls-Royce Silver Cloud II & Bentley S2 were quicker than most sports cars. By 1986, they were no quicker than in 1959, and also no quicker than most medium sized saloons (i.e. 0-60mph in 10-11 seconds). It was disappointing that fuel injection was not introduced on all models until 1987 model year, and then only a mechanical fuel injection system. Mercedes had been using fuel injection when the engine was first produced in 1959. Without turbocharging, the engine would have ‘died’ by 1998, or even earlier. Or, there would have been the need to develop the basic engine, such as the ‘twin overhead cam’ engine described above. For much of its life, this engine was felt to be of too large capacity and too little power. The lack of change was probably because of too little funds to develop the engine or produce a different one.
Turbocharging turned out to be the solution to both the engine’s and Rolls-Royce’s problems. ‘Pushing’ air into the engine by means of a turbocharger overcame the restricted air inlet to the engine, and gave significant increases in power. As will be explained in the ‘Turbocharging’ article, a turbocharger both increases the air ‘pushed’ into the engine and the engine’s compression ratio. The
power of an engine tends to be proportional to the mass of air it consumes – so more air = more power. The higher compression ratio tends, to a lesser extent, both increase the power and the efficiency of an engine. Thus, turbocharging increased the power of the engine, and allowed it to continue for 50 years. This must be a record for a production car engine.