Recently, Dr Ulrich Einhorn, Bentley Motors’ Member of the Board for Engineering delivered an interesting talk at the Sir Henry Royce Memorial Foundation Lecture. Titled The History of Another Dimension – 50 Years of Bentley’s V8 engine, this lecture took its participants through the history of one the most enduring engines of all time. After debuting in the Bentley S2 in the form of a 6.23-litre V8, the famous engine has since swelled to 6.75-litres, and is currently used in the Bentley Arnage and Brooklands.
A video playback of the lecture and its slides can be viewed from The Institution of Mechanical Engineers’ website. The video lasts for an hour and 19 minutes, but it’s well-paced, so it doesn’t feel draggy. Unfortunately, the picture and sound quality wasn’t exactly pristine, so listening to Dr Einhorn’s accented English might prove a challenge to some. There wasn’t much to ‘see’, because the camera was pointed solely at the talking Dr Einhorn. The slides available for download are in PDF format, so you can’t get the slide animations that were obviously there in PPT or PPS format. If you watch it, I recommend that you just occupy your monitor with the slides while listening to the sound at the background until the Q&A session.
Bentley & Rolls-Royce
The lecture kicks off by showing us the intertwining history between Bentley and Rolls-Royce. Both companies were founded seperately, but RR bought Bentley over in 1931. After the second World War, RR and Bentley moved into the now-famous production plant in Crewe, where Bentley has remained till now. In 1980, RR, and together with it, Bentley was bought over by British engineering firm Vickers.
Vickers decided to sell RR and Bentley in 1998, triggering a bidding war between Volkswagen and BMW. The complicated transfer wrangle eventually resulting in the split of the two names – the Rolls-Royce name and trademark going to BMW, while VW gets Bentley, the Crewe factory, and all associated intellectual properties. As such, the current BMW Rollers bear no technical or corporate relationship to the old ones.
4.56-litre F-head Straight Six
In the 1940s, Bentleys and Rollers were powered by a 4.56-litre straight six that was designed with a rather unique F-shaped cylinder head. This pushrod driven engine had the intake valve situated on top of the combustion chamber, while the exhaust valve sits at the side next to the pistons, creating a bizarrely shaped combustion chamber.
After 20 years of service, this engine was deemed insufficient to meet Bentley and RR’s needs. A new design was needed. In 1954, development work began on a new V8 engine with the goals of achieving 50% torque and power improvement, minimal increase in weight and cost, and undiminished noise, smoothness and reliability compared to the straight six.
Diagram of F-shaped head. Intake valve on top, exhaust by the side.
A couple of early V8 prototypes were developed and tested before a 6.23-litre unit debuted in the Bentley S2 and Rolls-Royce Silver Cloud II in 1959. This engine featured a 90-degree V angle, and had an aluminium block. It was designed to allow for a possible 15-20% output increase in its lifetime. Each engine was handbuilt in Crewe and then subjected to run-in and performance tests before being installed.
It is a common flaw among engineers when designing products to neglect taking production and maintenance difficulties into consideration. Bentley and RR, despite their lofty standards, were no exception to this rule. The design team was too busy coming up with a brilliant engine, that they neglected to think of the technician at the workshop who has to change the spark plugs.
In the S2, the front wheels have to be removed in order to gain access to the plugs. While this in itself is no major flaw, it does make life a little difficult for the maintenance crew. They must have made their feelings heard to the design people, because in 1963, Bentley rectified this problem in the S3 by angling the plugs to allow access from the top. The S3 was replaced in 1965 by the T1, but the venerable V8 was carried forward with some engineering modifications.
Restroked to 6.75 litres
In 1970, the engine was restroked to displace 6.75 litres and continued to see action in the T1, its successor T2, and its mechanically identical cousin – the Rolls-Royce Silver Shadow until 1980. Throughout the 70s, tightening emission regulations, especially in the US, saw the introduction of various emission reducing innovations into this engine to ensure that it remained compliant to regulations.
The engineers briefly flirted with the idea of designing a new engine to replace this aging powerplant. A smaller V8, codenamed L380 was developed by Porsche but was dropped because it could not simultaneously lower emissions and maintain previous power levels. They did manage the feat with the L410E engine, which was a 7.25-litre V8, but dropped it because the larger engine was judged to be ‘politically wrong’.
The year 1980 saw the take over of Rolls-Royce by Vickers. It also saw the introduction of the Bentley Mulsanne and the Rolls-Royce Silver Spirit. Here, the 6.75 V8 comes, for the first time, with Bosch’s K-Jetronic fuel injection system. In 1982, the Mulsanne Turbo, which produced 300bhp and 600Nm, was launched in the Geneva motor show. Then in 1985, came the Turbo R, which was rated at 320bhp and 660Nm.
BMW vs Volkswagen
The Rolls-Royce and Bentley engineers continued to develop and re-develop the V8 well into the 1990s. By 1994, it was producing 355bhp and then 420bhp by 1998 – which eventually turned out to be very interesting year. The Mulsanne was replaced by the Arnage, while the Rolls-Royce Silver Spirit was replaced by the Rolls-Royce Silver Seraph. The 6.75 V8 was replaced by a couple of BMW-sourced powerplants.
The Silver Seraph got the 5.4-litre V12 M73 engine, while the Arnage was fitted with a 4.4 V8 twin turbo that had engineering inputs from Cosworth. In his lecture, Dr Einhorn noted that Bentley customers did not like the high-speed nature of this engine, and the 6.75 went back into the hood in the form of the Arnage Red Label. Well, that’s not the full story.
At that time, Volkswagen and BMW were locked into a fierce battle to buy RR & Bentley. VW had already outbid BMW and won the battle. However, the Bavarians had managed to purchase the rights to the RR name and grille, and also threatened to stop supplying engines with a year’s notice. Eventually, an agreement was reached by the companies where BMW would take the RR brand, but Bentley and all the associated facilities and intellectual properties would remain under VW.
Under the agreement, VW will continue to manufacture RR and Bentleys until 2003, afterwhich, BMW will take over the rights to the RR brand. BMW also agreed to continue supplying engines for the Arnage and Silver Seraph. Knowing that they cannot have such an important division of their business taking engines from their rivals, VW quickly pulled the old 6.75 out of cold storage and shoe-horned it into the Arnage, ensuring that this old workhorse soldiers on
More Recent Developments
With the backing of the VW Group, Bentley has managed keep the V8 sufficiently up to date and still compliant with the latest automotive regulations. The current iteration of the engine features twin turbocharging, producing as much as 530bhp and 1030Nm of torque in the Bentley Brooklands. Far from being antiquated, Bentley claims that this engine complies to LEV2 emission regulations. Impressive, when you consider that an engine dating back to 1959 complies to 2004 standards.
After decades of transmission sourcing from GM, the engine is now coupled with a new 6-speed automatic transmission from ZF. The continued sourcing of GM transmissions have led to rumours that the basic architecture of this engine has been taken from existing GM designs of the day – a rumour Bentley is still doing hard to dispel. As of now, Bentley’s factory in Crewe still produces units of this engine entirely by hand
This year, Bentley celebrates the 50th anniversary of this remarkable engine. Despite twice coming close to being decommissioned, this engine has grown from strength to strength. It has retained the same basic block, but power and torque have swelled to three times the original outputs in 1959, and to think that it was only engineered for a 15-20% increase.
When it was introduced back in 1959, this engine was ahead of its time. It is a testament to the superb engineering and craftsmanship of the folks at Crewe that they have managed to keep it relevant 50 years on. Being one of the most powerful production engines in the world, this remarkable powerplant looks set to soldier on for quite some time before being retired. Even when it finally calls time, this enduring powerplant will stay in the memory of car enthusiasts for a long long time to come.
Once again, the video and lecture slides from Dr Einhorn’s lecture can be viewed [here]. Enjoy.