Citroën didn’t have an engine worthy of their nascent 1970 flagship, but it wasn’t for the want of trying.
The highly unusual structure and operation of Citroën’s Bureau d’Études may have created a number of technical masterpieces, but it equally resulted in a number of serious operational drawbacks; perhaps the most serious being the lack of a cohesive singularity of purpose. Not only did the nominal Rue de Théàtre headquarters lack an effective figurehead (notably so in Lefèbvre’s wake), but the bureau itself was apparently scattered across a number of locations around Paris, each very much in effect its own personal fiefdom.
Of these, perhaps the least regarded represented the double chevron’s longest standing and most glaring weakness – engine development. This department, led by Italian former Fiat racing engine designer, Walter Becchia, seemed a largely forgotten outpost; the last meaningful programme to enter production after the cessation of hostilities in 1945 being the air-cooled flat-twin, fitted to the 2CV and its derivatives.
Two primary issues confronted Becchia: that of resource (there being little shortage of talent or ability), the other being philosophy. Under Pierre Bercot’s leadership, Citroën’s image was that of technological pioneer. But the technology the double chevron espoused (at the upper end at least) was that of advanced integrated hydraulic systems and sophisticated chassis dynamics married to progressive, aerodynamic bodywork. The engine tended to be viewed as something of an afterthought.
The roots of this lay in France’s post-war economy. As the country rebuilt, government imposed strictures upon engine capacity and power output penalised companies (and in turn, customers) who produced powerful, large-engined, upmarket models. This led to a situation where large-capacity, multi-cylinder engines were no longer built in France – the domestic industry by consequence losing the skillsets required.
While the pre-war Traction Avant had been offered in 2.8 litre six-cylinder form, the DS19, from its 1955 inception was only offered with a four-cylinder 1.9 litre engine of relatively modest output, itself a heavily revised version of the pre-war Traction unit, designed by Maurice Sainturat. A six cylinder engine had been considered for the DS, but since an in-line unit couldn’t be made to fit, a flat-six prototype engine was built , but it failed to meet expectations.
As the French market recovered and customers became more affluent, the demand for greater performance grew, as did Citroën’s growing belief that the DS was poorly motorisée. Capacity was progressively upped and a fuel injection system developed, but Bercot wanted more; one notable sidebar to the S-Vehicle programme being a powerplant suitable for a flagship DS model.
Not that Becchia and his engineers had been idle throughout this period, designing and building any number of prototype engines, including units of both V6 and V8 configuration; the Italian engineer conclusively favouring the latter, described by chronicler, Jan Norbye as being “light, compact and powerful“. Both of these units were fitted to Jacques Né’s nascent S-Vehicle prototypes, as was a more powerful version of the DS in-line four.
Dubbed 15N, the 1987 cc unit employed twin overhead camshafts and a 16-valve cylinder head. Fitted with four carburettors and mounted into a standard DS, it went like the proverbial scalded Goddess. The second official S-Vehicle prototype was also fitted with this engine, by 1966 developing around 130 bhp and said to be the first Citroën vehicle ever to exceed 200 km/h.
According to Norbye’s account, it appears that Bercot was impressed, decreeing that it be productionised immediately, at least until he was faced with the costs of doing so. However, in its wake, elements amid Citroën’s management would allegedly became gripped by the idea of a cheaper, four-cylinder version of the forthcoming flagship, a matter which would impact notably upon its eventual design .
Meanwhile, Bercot concluded that an external supplier would be required to provide Citroën with a suitable powerplant, approaching a number of carmakers, including (it’s been suggested), Alfa Romeo, BMW and Saab. Approaching Tridente owner, Adolfo Orsi in 1966, the request was filtered through to technical supremo Giulio Alfieri at Viale Ciro Menotti, who despite not having being furnished with the name of the potential French client, immediately discerned its identity from the highly specific nature of the brief.
Bercot had stipulated a lightweight alloy engine of around 2.5 litres capacity, demanding a V6 layout, for compactness. It is at this point that one of the most durable misconceptions around the SM’s Maserati V6 engine arises. The common orthodoxy suggests that the engine supplied to Citroën was derived from an existing Maserati V8 unit. Not so fast.
When the request from Paris came through, Alfieri took a pre-existing 4.2 litre 90° V8 unit from his workshops, and by effectively slicing two cylinders from the block, fashioned a 2.9 litre prototype engine which effectively met the brief.  Within weeks, it was in the Rue de Théàtre. Highly impressed by the speed in which the Italians could work, an order for a number of additional engines was fulfilled, quickly fitted to Né’s S-prototypes. Bercot wasted no time, negotiating an engine supply contract before Maserati’s competitors had even got off the blocks.
However, while the subsequent production engine may have shared this unit’s included angle, it was in fact, new from the ground-up and designed specifically to Citroën’s specifications. The 2.7 litre capacity was arrived at to ensure an adequate power/economy balance coupled to the fact that it would lie within the French government restrictions on engine swept volume, above which punitive taxes would apply.
Bercot stipulated the engine must be no larger in physical size than the existing in-line four, that it should be as light as possible and must develop over 170 bhp. Alfieri chose to retain a 90° included angle, firstly because it aided packaging, both within the engine bay and around the engine itself and because it was a layout familiar to him. However, this was not an ideal included angle for a six cylinder engine, most V6’s employing a 60° vee, for sound technical reasons.
The prototype Maserati engine was fitted to a DS, but was found to be too powerful, resulting in what former Citroën executive, Jacques Fleury described as “precarious, unsafe handling“, and since it was decided that it would not be possible to successfully market a DS at the vastly higher price required, the S-Vehicle programme gained further traction at board level, quickly becoming a production inevitability.
For Maserati, Citroën’s interest was fortuitous. Facing significant costs in meeting upcoming US impact and emissions regulations, and with an ageing product line, the necessity for collaboration became glaringly apparent. For Pierre Bercot, it also went deeper than a simple engine supply arrangement. Why this was to become so, will form the basis for the next chapter of our story.
More on the SM here.
Sources and references:
Robert Opron L’Automobile et L’Art: Peter I Pijlman
Citroën SM : Jan P. Norbye
Citroën SM : Brian Long
Sa Majesté – Citroën SM : Peter I Pijlman/ Brian Cass
Citroën SM – Accidental Death of an Icon : Stuart Ager
André Citroen – Engineer, Explorer, Entrepreneur – John Reynolds
Maserati- The Citroën Years 1968-1975 : Marc Sonnery
 Source: Marc Sonnery.
 There were two flat-six proposals, employing both air and water cooling. Speaking with author, Marc Sonnery, Jacques Fleury intimated that the flat-six “was not a workable solution“.
 It remains unclear as to how far discussions got with other carmakers, but Alfieri’s initial cut down prototype V8-derived prototype still exists in an Italian Maserati collection. Source: Marc Sonnery.