A week before the public launch of our tera® quad-cam V12 at Race Retro outside Coventry and I asked myself, “Is the 12-cylinder engine dead?” I was about to introduce the tera®, Building The Legend Limited’s own unique quad-cam V12 engine. The type of power unit which could have been heard howling down the Mulsanne Straight at Le Mans in 1966 and beyond. But why did I embark on this craziness? Why design and build a V12 engine? Why the name “tera®”?
The last question is easily answered ….Can you think of a better name for one of these engines?
Naturally-aspirated and boasting a capacity of 6.1 or 6.8-litres (372 or 488 cu in) with power and torque in abundance. An electric motor may silently propel you forward more swiftly but certainly not with such a big smile on your face ….
When BMW M CEO Markus Flasch was recently asked if the BMW V12 had any life in it, he answered, “Beyond what we have, I don’t believe we will see a new twelve-cylinder model in the foreseeable future.” With the likes of Ferrari downsizing V12 models to a twin-turbo V8 and Lamborghini considering a V8 for their 2024 Aventador, we can be forgiven for thinking that the 12-cylinder is a powerplant of the past.
I completely understand that it’s not easy to justify 12 pistons these days …but, then, sit in the cockpit of a Ferrari 812 Superfast, a Pagani Huayra, or an Aston Martin DB11, or, dare I say it, …stand alongside a tera® … and put a finger to the start button.
Then listen to the resulting sound.
That, sir or madam, friends and fellow-enthusiasts, is the sound of life. The song of a living and breathing entity, the most soulful mechanical invention since the dawn of the Industrial Revolution. That is the melody of a dozen cylinders working in harmony, full of anima (the part of the psyche which is directed inwards, in touch with the subconscious) and heart and fury.
Even if it’s no longer the obvious choice (or even the most logical), the 12-cylinder lives …
In the past, a 12-cylinder engine was the only certain way to guarantee power and refinement. They propelled the fighter planes of World War I and II, and motivated early automobiles from Sunbeam to Packard to Cadillac. The Ferrari V12 was — and is — considered a hallowed Italian treasure, at least equal to anything inside the walls of the Vatican.
The late Cecil (Sam) Clutton , CBE wrote after driving a Hispano-Suiza Twelve, “There is an indefinable magic about every V12 I have driven, whether it is this one, or the [Rolls-Royce] PIII, or the splendid Packard, or the one-and-only 10 ½ -litre world speed record Delage”.
In this era, a V12 is no longer a necessity. All those super-chargers and turbo-chargers coax as much or even more power from smaller, more efficient engines which are lighter and less complicated.
This means that buying a car equipped with a V12 becomes a matter of CHOICE. You opt in because — just like the best watches — you love the connection with a long and wonderful history, a bridge from one bygone era to today—a little bit of a Supermarine Spitfire fighter lives on in your garage. It comes from the heart.
Wasn’t it Enzo Ferrari who proclaimed,” Every man should plant a tree, father a child and drive a V12 once in his life”?
Try to explain the magic of a V12 to a novice, and you may talk about the boundless torque, the ability to rev into the stratosphere, and the smooth delivery of power.
But soon enough you’ll turn to the sound, the defining element which simply can’t be recreated by a trick turbo. While each car model has its own personality, they share a glorious commonality. The smooth, basso profundo rumble at the start is followed by a rise in pitch and decibels as you coax the revs higher and higher.
Damon Hill said, “I don’t know what it is about V12s, but this arrangement delivers a peculiar pulse that is the sonic equivalent of strawberry mousse and cream”. “When I hear your 12 cylinders”, wrote conductor Herbert von Karajan to Enzo Ferrari, “I hear a burst of harmony that no conductor could ever re-create”.
At full tilt, a V12 produces a howl so sharp that it could cut meat from bone. And with a wide-open throttle, a roaring V12 resonates throughout the entire frame of a vehicle. It’s all around you—even your sternum vibrates like a tuning fork.
With the throttle pinned, the engine sends a thrum through the entire car – irrepressible, exultant…. magical.
The 12-cylinder lives
Perhaps the above goes some way to answering “why did I embark on this craziness?” It’s something that “just had to be done” … I’m sure most of my friends will “get it”. After all, for how much longer will we be able to buy one of these wonderful engines? As the large car manufacturers, egged on by vested interests and their governments rush headlong towards an all-electric future, our choices will become increasingly limited.
OK, so where did this idea for the tera® come from?
From the outset, the tera® aims to be a beautifully sculptural engine and unashamedly “of the period”. An engine designed to be seen and with a purposeful beauty hinting at the power lying within.
The tera® draws inspiration from Claude Baily ’s (former Chief Designer, Jaguar) legendary quad-cam racing engine – an engine designed to return the company to its glory days of Le Mans triumphs and domination. Before any of our “friends” at Jaguar make any sort of claims about the tera’s® origins, I should emphasise that the tera® is NOT a replica or copy of Jaguar’s prototype quad-cam V12 engine. Instead, it draws its inspiration from Baily’s stillborn engine as well as other engines of the period. Baily’s engine was meant to power the car which should have returned Jaguar to Le Mans – the XJ13 – also stillborn. The one-off car was destined to never turn a wheel in anger and the potential of Baily’s mighty power-unit was never fully realised. Instead, the company re-designed Baily’s racing engine into a SOHC version more suited to sedate applications.
In the words of Jaguar’s Walter “Wally” Hassan …
“… Between 1949 and 1957 Jaguar were actively involved in motor racing in order to create the sporting image for their cars. Amongst their successes were the winning of the Le Mans 24 Hour Race in the years of 1951, 1953, 1955, 1956 & 1957 as well as Sebring and many other international races and rallies. These cars were powered by the six-cylinder XK twin-cam engine and it was thought to be desirable to develop a successor to compete in future races, particularly Le Mans …. in order to provide the maximum potential in power, a 12 cylinder ‘Vee’ configuration … was conceived to provide for safe running at 8000-8500 rpm. By way of comparison the 6-cylinder twin cam XK engine had been designed without racing in mind.
… during the development period it was decided to withdraw from racing and these policy changes eliminated the need for a competition engine and emphasis shifted to the production (SOHC) version.”
Drawing inspiration from Baily’s V12 and other classic racing engines of the period, Building The Legend’s tera® represents an evolution of Baily’s concept. A “what might have been”. An engine born to race but whose potential was never fully realised – until now …
The engine is of course normally-aspirated and drivers of these cars will gain the full visceral experience of a howling V12 race-engine. Distributor-less with choice of period Lucas Mechanical or Electronic Fuel injection. Safe running rev-limit of 8,000 to 8,500 rpm. Available from street-spec to full-race.
The engine’s weight is similar to the classic iron-blocked 6-cyl engine . It can be installed in cars as diverse as the S3 V12 E-Type, XJ12 Coupe, V12 XJS and many other classic Jaguar saloons such as 420G and Mk10. It can even be installed in 6-cylinder cars with some modification (6-cyl E-Types included). Quad-Cam V12-powered XK120 anyone? Or a twin-engine power boat? The engine does bear cosmetic similarities to those powering classic V12 Lamborghinis and Ferraris ….
Applications of this engine are limited only by your imagination!
• Capacity: 6.1 L (372 cu in); 6.8 L (415 cu in)
• Bore x Stroke: 96 x 70 mm (3.8” x 2.8”); 96 x 78.5 mm (3.8” x 3.1”)
• Power: 350 – 650 hp (261 – 485 kW)
• Torque: 300 – 600 lb ft (407 – 813 Nm)
• Compression: 12.7:1
• 2-valve, over-square architecture, duplex-chain-driven cams with convenient Vernier adjustment.
A Bit of Background …
Before the V12, Jaguar’s racing and practically all road cars were powered by the powerful and renowned XK straight-six double overhead-cam unit. This engine had its origins in pencilled sketches drawn during the Coventry Blitz by Sir William Lyons and his engine designers; William Heynes (Chief Engineer), Walter Hassan and Claude Baily. These sketches and original designs were followed by working prototypes as early as 1943. The first 3,442cc production unit saw the light of day in the beautiful XK120 of 1947. The same basic engine continued production into the 1990s.
As can be seen from the original drawing from my own archive reproduced below, Jaguar ended up with a design where both inlet and exhaust valves were inclined towards the centre-line of the hemispherical combustion chamber at 35°. This was changed to 30° inlet and 45° exhaust for the ultimate “wide angle” head used in racing engines. The valve angle was modified simply to allow the use of larger inlet valves.
In the 1950s/60s this hemispherical type of combustion chamber was considered ideal for high-performance engines because of reduced valve “shrouding” compared to a “flat-head” design and a low surface-area to volume ratio. As can be seen from the following photo taken of a head I sectioned, the ports and valves were arranged more or less in-line across the engine. However, Harry Weslake worked closely with Jaguar when the engine was being designed and he introduced a curvature to the inlet port in an attempt to allow charge movement inside the cylinder (“swirl”). This was done to aid combustion efficiency and is evident in the photo.
Weslake’s modification, whilst introducing swirl, was compromised by the need to place the spark-plug off to the side so as not to interfere with the valves. A central spark-plug would have been ideal in this situation. Many designers of similar engines tried to improve the situation by introducing a second spark-plug on the other side of the chamber but this was never really successful. As owners of XK-engined cars will testify, these engines seem to prefer richer mixtures and rather a lot of ignition advance (10° and more). This generally indicates combustion is not as good as it could be. In the end, Jaguar’s “wide-angle” racing head probably reached the end of its potential because it could breathe better than it could burn.
Food for thought …
A bit more food for thought
See the very limited water passages in the above photo as well as the large amounts of metal in the casting? Square exhaust ports? Nowadays, and especially with the advent of 3D visualisation using tools such as CAD, it is possible to design optimal ports and heads with far greater and more efficient cooling surfaces – as well as optimal air flow characteristics.
Wheras the thinnest port walls in the XK head are more than 10mm thick, today’s cylinder heads tend to be closer to 4.5/5.0mm with considerably increased cooling surfaces. Whilst I don’t pretend to be any sort of expert in this field (in no way!), it seems to me that the port shapes, by today’s standards, could also be improved?
One thing which did work in the 6-cylinder engine’s favour may have been the side-entry and curvature of the inlet port which assisted combustion. In common with other engine designers of the period, Jaguar’s Claude Baily anticipated that further improvements could be made to this basic design by making use of down-draft porting. Baily adopted this when he designed his successor to the XK engine – the quad-cam V12. In theory, there just had to be a benefit of down-draft porting but Baily (and other designers) found these benefits weren’t achieved in practice. Flow may have been excellent but this arrangement simply didn’t allow useful swirl/charge-movement within the cylinder and combustion suffered as a result. Others who wandered down this cul-de-sac included Ferrari, BRM, Matra and Ford – Jaguar wasn’t alone in this.
A breakthrough came from work carried out by GM’s Sam Heron in the 1950s (Heron became famous for his work with aircraft piston engines and the sodium-cooled exhaust valve). Rover were probably the first to adopt his scheme which consisted of a flat cylinder head with the combustion chamber in the piston crown – a feature later adopted by Jaguar in their first SOHC V12 engines.
These heads became known as “Heron Heads”. In the mid-1960s Ford (of England) adopted the Heron layout for their entire range of engines. A close relative of the Heron layout was the very successful Repco V8 engine that powered Jack Brabham’s team to two F1 World Championships in 1966/67. Why was this basic layout found to be better? The increased combustion efficiency as a result of increased swirl and charge-movement may have pointed the way. It is all very well having superb flow, but this is to no avail unless the charge can be adequately and rapidly burnt.
Jaguar later improved the efficiency of their V12 further by adopting Michael May’s “Fireball” combustion chamber. In this design, the exhaust valve is deeply recessed into the head, forming a compact oval chamber with the spark plug at one end. As the piston advances up the bore it forces some of the charge into a shallow channel around the flush inlet valve from where it is squeezed tangentially. This creates a high-speed vortex in the combustion chamber – LOTS of movement and “squish” here …
Could it be possible to design a down-draft, hemispherical head with the necessary degree of charge-movement to allow combustion to match this design’s superior flow characteristics?
More food for thought …
The tera® Project – Ground Rules
The plan was to end up with a quad-cam V12 inspired by Jaguar’s prototype “XJ13” V12. We aren’t trying to re-invent any wheels here or produce anything approaching “state of the art” but, instead, a reliable fast-road/race engine which shares the same basic architecture of Baily’s prototype quad-cam and Jaguar’s legendary XK 6-cylinder engine (as well as others of the period). To this end, we are setting ourselves some basic ground rules:
- We are producing cylinder heads only. These heads will bolt directly onto Jaguar’s later SOHC V12 block. This means the heads may have applications other than the XJ13 – twin-V12-engined off-shore powerboat anyone? Quad-Cam XK120?
- Whilst remaining true to the basic architecture of Baily’s quad-cam (as well as others of the period), opportunities to improve gas flow, combustion and overall efficiency in the light of current knowledge were taken. Whilst cosmetically similar, these will not be exact copies of Jaguar’s quad-cam prototype engine.
- As was the case with the original XJ13 engine, cam drive is via duplex chain.
- Two-valve, hemispherical head design.
- Fully programmable fuel injection & ignition (prototype quad-cam uses a pair of 6-cyl distributors and Lucas mechanical fuel metering unit – the engine is designed to offer this an option too).
- Normally aspirated.
Because we were starting with an almost clean sheet of paper, we had the opportunity to go back to first principles and consider things such as optimal valve sizes, port configuration, charge movement and spark-plug positioning etc.
The first step was to draw up a pair of heads combining a SOHC V12 mounting face with the basic 6-cyl DOHC design just to see if everything could be made to fit. After all, we don’t want to end up with head studs coinciding with inlet/exhaust ports! Also, we needed to make sure it was practicable and possible to mate up with existing SOHC V12 oil and water passageways. There are also practical considerations to consider such as being able to access head nuts – bearing in mind each SOHC V12 head is fastened down by four rows of head studs but only two in the prototype quad-cam and XK 6-cyl.
The V12 head is not only longer than the 6-cyl head, but the bore positions are different. (Incidentally, the SOHC V12 shares the same bore spacing as the prototype quad-cam – a SOHC crankshaft fits). Positions of water and oil passages are very different between the XK 6-cyl and SOHC V12. The biggest challenge was combining the two heads so that the V12 stud pattern was maintained. It became evident very early on that the new quad-cam engine will have unique cam covers as well as custom cams.
The following pictures of the prototype quad-cam V12 show what we hoped to end up with – or, at least, something close:
In contrast to the 6-cyl XK head and the SOHC V12, oil is fed to the quad-cam heads via a drilling passing from the gallery to each head. The later SOHC V12 scheme will probably be used in the new engine. The new engine will probably use separate cam bearings as with the 6-cyl XK head (no cam bearings in the SOHC V12). The following pictures show the general layout of these initial designs. They are just preliminary designs with no attempt to optimise things like port configuration, spark-plug location etc. They showed it would be possible to design our own heads which would bolt straight on to the SOHC block. Discussions with a local foundry highlighted consideration we need to build into the design. Further discussions with pattern-makers confirmed it will be possible to produce the necessary patterns etc.
Learning from the Master …. Ex-Jaguar and Coventry Climax’s Richard Hassan (son of Jaguar’s late Walter “Wally” Hassan).Richard followed in his illustrious father’s footsteps becoming a talented race engine designer and developer. He joined Jaguar in 1957 as an Apprentice before joining British racing driver and racing team owner John Coombs in 1969. A year later he moved to Coventry Climax (which had become a division within Jaguar) and worked on many of their legendary racing engines. Richard set up on his own in 1977 and continues to run his own successful engineering business in Coventry.
First run ….
For details, availability, applications and pricing contact:
Complete, tested, warranted tera Quad-Cam engine – “plug and play”
Complete fully built-up, tested & warranted engine.
Engine removal/installation/commissioning services are available.
More info here
Contact us for details: