A closer look at the SM’s Maserati-sourced V6 engine.
Like most aspects of historical record, the story behind the development of Maserati’s 114-series 2760 cc V6 engine is dependent upon whose account one reads; the orthodoxy suggesting that the engine supplied to Citroën was a derivation of an existing Maserati V8 unit. However, its bespoke basis has been placed beyond doubt.
When the request from Paris came through, Maserati technical director, Giulio 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. However, while the subsequent production engine may have shared the original 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. 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 smoothness of operation.
A primary stipulation from Quai Andre Citroën was for a compact and lightweight unit, physically no larger than their own in-line four. With the 114-series V6, the architectural layout chosen by Alfieri allowed these strictures to be met. However, this brought forth a number of structural and operational compromises – one in particular proving something of an expensive error.
Owing to the 90° included angle between cylinder banks, it was prone to uneven firing intervals and a lack of smoothness at certain engine speeds. It was therefore decided to carry the counterweighting on the four bearing crankshaft and accept the uneven firing intervals. The major engine components; cylinder block, crankcase and heads were all aluminium pressure castings – the cylinder heads being interchangeable. Cast iron liners were press-fitted into the block, the flat crowned aluminium pistons giving a 9: 1 compression ratio.
Sufficient breathing was an important design priority; one advantage of the wider included angle being that it allowed additional space in the vee for ancillaries and in particular, induction porting. The V6 followed normal Maserati practice in that it employed four chain-driven overhead camshafts, the cylinder heads allegedly being designed in such a way so as to be capable of allowing for larger valves or a four-valve layout if necessary. There was also provision for a longer stroke version, bringing the swept volume up to 2965 cc.
Induction was via three dual-barrel Weber 42 DCNF/2 downdraught carburettors, and in 114/1 specification, produced 170 bhp (DIN) at 5500 rpm. In mid-1972, a revised version was fitted with Bosch D-Jetronic fuel injection (114/3) for European markets, which saw maximum power upped to 178 bhp (DIN) with a slight improvement in torque. The same year, the SM was introduced into the US market with the 2965 cc unit (114/11), developing 190 bhp (SAE) on triple Webers, mated to a Borg Warner 3-speed automatic transmission. The complete engine, made up of 1140 individual parts came in under 140 kilograms, 25 kg less than the later PRV unit as employed by Peugeot, Renault et al.
Where the 114-series unit differed most notably from standard Maserati practice (and underlines its unique construction) is in its camshaft drive, which is mounted centrally, running the entire length of the block. In addition to providing drive for the camshafts (via three individual duplex timing chains), this shaft also powered the main hydraulic pump, water pump, alternator/generator, and air conditioning pump. On US-specification models, it drove the air-injection pump for the emission controls.
But it was the 114-series engine’s camshaft drive that was to prove its Achilles heel, more specifically the chain tensioning arrangement. With the key design work completed and prototypes built, the bulk of development and proving took place by Citroën engineers in France, much of it around the Mont Ventoux in Provence. A huge amount of development miles were amassed, the engine proving to be wholly satisfactory, which begs the question of how the issue failed to materialise.
Chronicler, Peter Pijlman suggests that Alfieri had warned the Bureau d’Études about the primary chain tensioner, but that his advice to use a stronger component was ignored. He states that Citroën’s rationale was that they had used this version extensively in the DS with no problem. However, this was a completely different proposition – a modern high performance engine, it being deemed “unfit for this type of chain tensioning” by former Alfieri cohort, Anacleto Grandi.
According to Grandi, the gear teeth within the tensioner would degrade over time as the engine heated and cooled, causing the teeth to jump, ultimately leading to a meeting of valves and pistons. Thousands of engines failed in this manner, arriving back in Modena to be rebuilt. It took some time for these problems to come to light, but once they did, it was a huge blow, to Citroën, to the reputation of the SM and to Maserati.
Nevertheless, Maserati technicians quickly discerned the cause and by employing a different tensioner design the problem disappeared. However, for the SM, permission to implement the fix was not forthcoming from Paris – the edict being to repair the engines but not to modify them. Politics once again reared its head and would be to both SM and Maserati’s detriment.
One noteworthy development was that of a 1999 cc version of the 114-series engine which was produced for the Italian market to circumvent motor tax laws. Developing 159 bhp (DIN) at 7000 rpm, it was fitted to the Maserati Merak, but unsurprisingly proved no ball of fire. However, could it have potentially allowed for a cheaper, entry level SM?
A further (stillborn) development, was the fitment of the 114-series engine into a prototype Citroën CX. By 1975, Maserati engineers, desperate to maintain the company’s viability, created what was known as Vehicle L, which had an adapted version of the V6 which could be fitted into the CX’s engine bay, using the same engine mounts. It was evaluated by Peugeot management, but by that stage the game was up. Sochaux had their own ideas.
 Alfieri’s initial cut down prototype V8-derived prototype still exists in the Italian Panini collection. Source: Marc Sonnery.
 While the 3-litre unit was the largest capacity version of the 114-series fitted to the production SM, Maserati built a 3.2 litre version for their stillborn Quattroporte II model. [Source: Marc Sonnery]
 [Source: Marc Sonnery]
 A number of experimental four-cylinder versions of the 114-series were also made and fitted to prototype Citroen CXs. [Source: Marc Sonnery]
 There were apparently two prototypes, one with a transversely mounted V6, the other longitudinal. [Source: Marc Sonnery]
Sources and references:
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
Maserati- The Citroën Years 1968-1975 : Marc Sonnery