Theme : Engines – France

Do French engines live up to that nation’s fine engineering heritage?

1913 Peugeot twin OHC 16 valve 4 cylinder
1913 Peugeot twin OHC 16 valve 4 cylinder

In Post War Europe, engines were restricted by reasonably arbitrary taxation classes. In Britain, the old ‘RAC Horsepower’ rating was based on an archaic formula that related to the bore only, not the stroke and didn’t actually refer directly to the output of the engine.

Despite it being abolished in the late 1940s, it meant that the longer stroke engine, with its relatively low rev limit, lived on far longer in much loved stalwarts such as the Jaguar XK and BMC A Series and it did stem the development of lighter, freer running engines.

Italy was less prescriptive and, although there were aberrations, like home market only 2 litre Ferraris and Alfas V6s, it allowed the development of the sweet engines found in the Alfas and Fiats of the 60s. The French tried to be more scientific, with a fiscal horsepower tax that brought in various factors but, generally, encouraged smaller engines of 4 cylinders and less. Thus, in a country that has a fine record in technical advances in motoring, engines struggled to keep up.

Citroën, when they actually were producing truly ‘Créative Technologie’ twenty-five and more years ago, did not generally match their adventurous cars with the engines. The 2CV flat twin was a fine engine – clever, rugged, characterful and able to be repaired by those of modest skill, such as me. The spiritual big brother, the air-cooled flat four of the GS of 20 years later, was also fine in its way but, in hindsight, that incredibly advanced small saloon should have had something quieter – in other words a water-cooled flat four or the Wankel engine that was planned. Big Citroëns however were not well served. There is a direct descendancy from the wet liner four used in the 1934 Traction to the engine of the last CX GTi Turbo. This was a fair, but not outstanding engine at the start. By the time it died it was producing an impressive amount of power, bearing in mind its rudimentary design, but not with any degree of smoothness or economy.

Citroën’s historical excuse for the unseemly longevity of its wet liner four is that the carry-over of the 3 bearing unit from the Traction to the original DS was unintended, being an eleventh hour decision when it was realised that the proposed air-cooled flat 6 was not going to materialise. In fact the flat 6 would have been mounted ahead of the engine and, as such, the front part of the car would have been engineered very differently. Therefore the dumping of the intended engine was more like a ninth hour decision, which could have given them more time to better update their 20 year old engine. However, as was always the case with Citroën, it’s likely that funds were low and a pragmatic choice was made.

Another 20 years later, and the carry-over of the now 5 bearing unit from the DS was intended as a temporary measure until the proposed rotary engines for the CX came on line. Unfortunately the Comotor project turned into tragedy as reliability and fuel consumption became insurmountable issues. The futuristic CX was therefore, in larger capacity form, condemned for the whole of its lifespan to a rough push-rod engine whose roots, by the end, went back over half a century.

The only other Citroën powerplant of note was Alfieri’s V6 Maserati engine for the SM, which was an excellent and unfairly underrated engine, compact, flexible, fine sounding and produced in record time (not, incidentally, by sawing two cylinders off a V8 as the myth goes) but it would have benefited from a capacity of maybe 3.2 litres, not the 2.7 litres that French tax decreed and, anyway, it was not a French engine.

From the mid Seventies onwards, Citroën were of course using whatever engines its new masters, Peugeot, saw fit to let them have. The best you’ve usually been able to say about mainstream Peugeot and Renault engines is that they do their job, though that should be seen as faint praise as long as they do it without fail – much as I love the Citroën twin, the four cylinder of the Renault 4 arguably did all that engine could do, but at a more civilised noise level.

In the Sixties, Peugeot were early to produce a fuel injected petrol engine for the 404, which impressed testers. However, the growing unimportance of engines to PSA and Renault came to its peak in the next decade with the Douvrin four. Previously proudly independent, here were two manufacturers deciding that what went on under the skin maybe didn’t interest punters that much, so why not split the development costs?

In fact this had a then recent precedent in the Comotor project between Citroën and NSU but, whereas that was a brave undertaking that unfortunately failed and brought down two fine companies, this was to be an exercise in penny-pinching and playing safe. Passable beyond belief, the Douvrin engine behaved just like you’d expect of the committee specified device it was. It had a V6 brother, the PRV, whose only similarity to the free revving Maserati V6 was its 90 degree cylinder configuration. It could be tweaked and tuned to be quite sporty and exciting but, in its natural form, like its small brother it was outstandingly ordinary.

Nevertheless, it might have been nice for Peugeot to let Citroën fit it into the CX for a bit of the six-cylinder smoothness it craved but this never happened, supposedly for fear of affecting Peugeot 604 sales.

Sometimes, if not quite at present, Renault might be at the top of Formula 1 and their hot hatches might be breaking Nurburgring records, but that just makes the stultifying behaviour of their everyday engines all the more grating, and only excusable when they work. Nigel Mansell’s World Championship was made particularly irritating for me at the time by a persistent and hard to diagnose misfire in a well maintained 6 year old carburetor fed Douvrin-engined Renault Espace. That was one breed that racing hadn’t improved. All the recent Renaults that I’ve driven seem to be biased more for the convenience of marketing folk able to tout unachievable fuel consumption figures, than for my comfort or pleasure.

Anyone reading the above might notice the lack of reference to diesel and, of course, the French were early adopters in the DERV revolution, with Citroën taking the dubious accolade for the first diesel car in 1933. Then followed a lull, since diesel was not offered in the Traction or DS, and it wasn’t until 1959 that Peugeot really got the French industry going with diesel and, relatively speaking at least, offered better performance over the next few years than their only real competitors in oil-burning, Mercedes.

From then on there was no looking back and, for the next 30 years, Peugeot, then PSA, were at the forefront of developing car diesel engines that were, at least, half civilised, and employing them in their cars and those of other manufacturers.  I do however agree with our Editor that a diesel will never be more that half civilised.

The other half is busy belching out carcinogens whilst teams of engineers toil to diminishing returns to filter them to acceptable levels. The low fuel consumption of early diesels might actually have been matched by petrol engines, should you have driven them at the pitiful performance levels that diesel then allowed, a task that would have been made easier by the horrendous understeer risked from having an extra 80kg under the bonnet.

However, in France, the situation was skewed because diesel was considerably cheaper than petrol and, moreover, the Government favoured it with beneficial fiscal horsepower figures, encouraging more and more ingenuity from engineers. Thus we’ve ended up with motors that seem remarkable when compared with those that you’d have found in a Peugeot 405 GRD of just 25 years ago. This is where the considerable talent of the French industry has been concentrated, and it has led the World, but I’m not sure that history will thank them for this.

Citroën Flat Twin A rare example of a great French engine?

Because a PSA XUD7 1.8 litre 4 cylinder diesel is not a great looker, this piece is largely illustrated by grand engines from France’s distant past. These impress in both specification and appearance, especially when buffed up to Pebble Beach standards, but they were always intended for a select and wealthy minority. To produce engines for everyman is a more worthy task and, on many levels this is what France has done. However their emphasis on oil-burners means that, in my eyes, it is Italy and Japan who take the honours as the great small engine manufacturing nations.

24 thoughts on “Theme : Engines – France”

  1. Nice essay. Having looked into the consequences of a poor or limited engine range, I think France paid a heavy price for discouraging larger capacity engines. They killed their specialists whereas the UK and Germany kept theirs. And the anonymous Douvrin units assumed an indifference to customers the equal of GM USA with their Iron Nail. And by sharing engines Renault and PSA restricted their freedom in packaging and ceded an area of competitive advantage. The Renault 25, 605 and XM trod on each other’s toes and were all equally weak in the face of German competition.

    1. Indeed, The French industry had to look outside France on the few times it decided to go for something more exotic. To Chrysler for the Facel Vega, to Maserati for the Citroen SM, to Ted Martin in the UK then to Chrysler for the sadly ill-fated Monica. The only truly exotic French engine from the second part of the 20th Century was the Matra V12 racing engine. But really it is is their general avoidance of the distraction of such fancy vanity projects, in favour of good democratic transport, that was always one of the French industry’s most praiseworthy attributes.

  2. Interesting piece. I’d never realised that the CX never received a V6 engine, and how it was prevented from fulfilling its potential with anything other than 4-pot engines.
    On the other hand I noticed a long time ago that small engines in Peugeots and Renaults from the late 70’s and early 80’s all sounded the same, something which I found highly intriguing even at a very young age…

  3. In my work as a classic car journalist, I’ve created the latest Citroën-only magazine in France, “Chevronnés” (you can flip through the pages of our last issue here : So, I’m in touch with quite a few Quai de Javel engineers of the great “Michelin” era. By the way, I’d like to correct something I’ve read quite a few times : the Traction engine and the DS 21/CX engine are not the same. In fact, they do not share any common part. Obviously, they have a few specs in common : both have an iron block, an OHV arrangement with alloy head, hemi chambers and v-angled valves, wet liners, but that’s about it. In fact, the so-called “Traction” 3-bearings engine still has a quite long stroke (100 mm), whereas its 5-bearing sibling is always oversquare.
    Therefore, they definitely should be viewed as two different engines.
    Moreover, talking about other proposed powerplants for the CX, it is true Citroën wanted to put a rotary engine in it, but it was a twin unit, not the allegedly three-rotor, which never existed. In fact, the one tested in the CX was the same used on the helicopter project, with a unitary displacement of roughly 600 cc and 170 hp, which gave it performances quite in the GTI Turbo league ! Citroën made as well a few V6 prototypes with the Maserati unit used on the SM, and even thought about putting the PRV. But both arrangement were soon proved quite difficult : with the big crossmember (where the spare wheel is), these engines needed to be strongly lean forward, which gave them lubrication problems.
    By the way, in our country, the PRV had a truly awful – and completely unfair ! – reputation. Most french journalists hated it because in its first versions, it was a bit rough, thirsty and didn’t like high revs. Peugeot, Renault and Volvo wanted a strong and reliable unit, two qualities the PRV had in droves ! Gérard Welter (of WR/WM Le Mans racer, and boss of Peugeot styling department) told me that our good old six could be tuned infinitely, up to 900 hp, with an ordinary production block. Originally, the PRV was especially dismissed for its uneven firing (which lent to a heavy flywheel, to counteract vibrations, but didn’t help it to rev freely). But, in the eighties, it became a very competent 6-cylinder, if still a bit thirsty (the bispherical combustion chambers, with its valves not really in front of each other and reclined spark plugs being the main culprits), noticeably when it was given finally an “even firing” crankshaft arrangement, first on the Renault V6 Turbo, then on the lovely but sadly underated 505 V6. It was probably too little, too late, and the PRV soldiered on as our unloved big engine. Which is a shame, as it did nothing to help our latest sports cars, Alpine or Venturi, these having already to battle against brands that have purposedly-built sports engine with a 6-cylinder that was originally designed for big execs, not for out and out sports cars…
    We french have a very strange behaviour : we always tend to dismiss our own achievements ! In fact, the same story can sadly be written on our last V6 project, the “ES/L”, used on 406, Xantia, XM, 605, Clio, Avantime, C6 and a few others : a very capable 6-cylinder, completely overlooked by our own brands. This is typical PSA and Renault madness.
    Sorry for that lengthy answer, I could go on for hours…

    1. Thierry. No apologies needed for your excellent comment. Welcome to DTW and thank you for the kind words you expressed elsewhere and I look forward to buying a copy of Chevronnés next time I’m in France.

      My take on the CX engine is that it was a case of ‘my grandfather’s axe’ – the head and the handle have been changed at different points many times, but it’s still essentially the same axe. Likewise, the final CX engine’s morphing from the Traction unit never saw a completely clean sheet design. But do correct me if I’m wrong – we’re as happy to learn as to preach at DTW!

      As you’ve doubtless noticed, there’s a significant French car bias here. It’s interesting what you say about the French dismissing their achievements. My view is that the French industry was once supremely confident, producing interesting cars that it felt people needed, rather than just reacting to uncritical demand. Somewhere along the line, it either lost that confidence, or became more cynical but, as you’ll also probably have noticed, most of today’s offerings from Peugeot, Renault and, most disappointing of all, Citroen, leave us cold.

    2. “We french have a very strange behaviour : we always tend to dismiss our own achievements !”

      Maybe so, but in this case you listed all the reasons why the PRV V6 is generally dismissed, and they are mostly good ones.

    3. You command of the English language is top notch by the way – now that’s an achievement. Give yourself a pat on the back.

  4. That’s the thing with car history : you never stop to learn. And I’m learning something new everyday.
    Anyway, the PRV had quite a few big redeeming qualities : immensely strong, reliable, infinitely tunable, quite compact (roughly like a 50 cm cube). The original version weight only 152 kilos, and its power to weight ratio was seen as something pretty interesting for aeronautical purpose : a few plane makers studied it for their use. Moreover, it is still the fastest ever engine in the Hunaudières, partly by the added chicanes, but quite an achievement though.
    To me, it only needed bigger and sooner investment to became one of the very best 6-cylinder of its era.

  5. Let’s figure out things this way : was really the Cologne or Essex Ford sixes, the Opel straight, the frail Rover 2300/2600 or the Mercedes offerings of the 70’s (and even for most of these, 80’s) ten times better than the PRV ?
    Moreover, if you compare closely measured figures made by magazines in these days, you’d be surprised : most of the time, the french/swede engine would keep up even with BMW straight-six on performances, even with much less power. On the other side, most rivals sixes were not quite as thirsty, to be honest…

    1. The Ford V6s, especially the Essex versions, certainly weren’t great. Neither the Rover units though, as with most BL developments, a brave attempt by clever engineers in the face of tight-fisted management. The Opel was an interesting bywater with its cam in head pushrods. But all these and the Mercedes engines traced their history back a lot further than the Douvrin unit which was a clean sheet design. I get the idea that, because it had to be designed for so many applications, in its basic form it was compromised and should (and, when fettled by others, could) have been a lot better. It wasn’t a bad engine at all, but 1974 was possibly the worst time to introduce an engine that didn’t put good fuel consumption as a priority!

  6. Certainly, the timing was bad. You needed to have an already gold-plated reputation like Merc to be able to launch any kind of “luxury” car in those days. This is certainly one of the reasons the Lancia Gamma or later the Alfa 6 were kind of undercooked, two lovely barges that are discussed somewhere else here. These two being among the countless strange cars I love, again this blog was tailor-built for me !
    I confess a true passion for doomed cars, especially tiny and big ones. As long as it’s not german – with a few exceptions… – that’s fine for me.
    Anyway, a bit more on the Traction/DS/CX engines : as far as I know, the “3 bearings” and “5 bearings” types are of the same school of thought, but really different. There’s not a single part that can go from one to the other, and these two even looks and sounds quite differently. And any Citroën engineer from that era I’ve talked to is very vocal about that important difference.
    Still, both are quite rugged and rough running, but they have slightly different behaviour : the older feels more torquey at slow rpm, but really hates to go beyond 4,500 revs. The “5 bearings” generation seems a bit gutless under 2,000/2,500 rpm, but feels less strained until 5,500 roughly. That’s why for a leisurely drive, an old DS (before 1965) feels better, more relaxed than a late DS 20. The 21 and 23 being much more pleasant at low revs.

    1. It’s an interesting discussion as to what actually constitutes a ‘new’ engine. If there is really no interchangeability I’d have to concede that the 5 bearing was a new engine, even if it was conceptually so close to the earlier unit. Why wasn’t it more advanced then? I suppose by 1965, Citroen had already started Comobil with NSU, so it was seen as a stop-gap. Why spend a lot of effort looking into overhead camshafts, etc, just use what you knew worked? The first time I was driven in a DS was in a reasonably new, 5 bearing Safari. It was a slowish drive (60-80 kph) and I remember the engine didn’t sound comfortable. I was disappointed. My prejudice against it probably goes back to then!

  7. My all-time favorite car was, is and will forever be the DS. But I admit that it obviously never had the truly good engine it really deserved. I’ve grown up in an Alfa 1750 Berlina, and I’ve owned two (a 1.6 Alfa 75 and a “916” GTV 3.0 24v), so I know what “good engine” can mean. Anyway, talking about “5 bearings” DS engine, there is really a surprising difference between the 20, quite hollow at low revs, and the 21 and 23 versions, which have really more “oomph” under 2,500 rpm. And the same thing can be seen at the wheels of CX’s : there difference is really surprising between a 2 000 and just a simple 2 200… That way, the top of the range DS and CX finally got reasonably lively engines, although not refined nor especially revvy.
    So, why not a true novel design back in 1965 ? I think you’re very true : Pierre Bercot, as it seems, thought the Wankel to be the next step. However, the engineers at Citroën designed quite a lot of advanced conventional engines, 4 cylinders, even sixes, with OHC, DOHC, etc… but these never got beyond the prototype phase. Moreover, from roughly 1967, Citroën had plans to produce the G engine for the GS, and the C114 at Maserati for the SM : already two new powerplants, which meant quite heavy investments.

    1. I’ve always imagined that, had they managed to iron out the problems with the flat 6, that alternative DS would actually have been a rather nose-heavy car, and maybe not as attractive or as nice to drive. So maybe that was a fortunate fluke of history

      It would involve a lot of chassis and bodywork modification, but has anyone ever attempted to create a Flat 6 DS (with a Porsche or Corvair unit)? I know that people have done C114 transplants and the Maserati engine is surprisingly tractable and not at all highly strung – with development it could have been a suitable engine for a top end DS, but probably too expensive. Do you know of any other interesting transplants into a DS?

      Incidentally, Bercot seems an interesting man. I have a copy of a book “Vieillesse Du Prince” which is said to be written by the same man, but my French is far too bad to appreciate it – or otherwise.

  8. Ahah, a 911-engined DS, like the originals VGD prototypes ! I thought about it for quite some time, but I never heard about someone who has tried to create one such a car. Probably it would required a huge work, just because of engine location : the production DS has the gearbox upfront and the engine behind, whereas the original project was the opposite. And I doubt it could be possible to put a Porsche flat-6 that way.
    Anyway, we have seen strangest things happening on classic car projects, so who knows ?
    In fact, somebody in Austria has managed to shoehorn a Citroën 15/6 (aka Big Six) in a ID 19 shell, in the eighties. The car had an huge bulk below the dashboard, and a big scoop on the bonnet, was finished in black and had a canvas top. I just don’t know what became of that incredible car. It was said that it used three carburettors, and was capable of doing more than 110 mph…

    1. That sounds insane. What happens to the car aerodynamically at those speeds? The roof and tail have the wrong sort of profile, don´t they?

  9. One question that comes to mind is if the 4-cylinder Douvrin was related to the V6 which was in turn originally conceived as a V8, would it have been possible to develop dieselized versions of the V6 and V8 as was the case with the 2.1 4-cylinder Douvrin?

    It is also interesting to note that Citroen looked at developed a V8 derived from the DS/CX engine, the latter would also go on to spawn dieselized variants along with a shelved 1.6 petrol variant planned for Citroen’s F project.

    Speaking of 6-cylinder engines NSU apparently looked at a flat-6 for the NSU Ro80 as an alternative to the rotary engine, it is pity that Citroen and NSU decided to establish Comotor together rather then work on other projects such as the flat-6 or even the (later VW) K70’s 4-cylinder engines.

    1. For Citroen and NSU the flat sixes would have made a lot of sense indeed. Where would a V8 fit in a CX? Or would it have been a small V8?

    2. It likely would have been a small V8 (curiously of 3-litres rather then 2.7/2.8-litres) though the DS/CX engine could have potentially reached 5-litres if necessary based on the path of the 2.5-litre 4-cylinder units, however Citroen did not have the resources to put such an engine into production on it’s own yet things might have been different with NSU in the picture.

      Unfortunately it is difficult uncovering more information regarding the NSU Flat-6 engine, apparently it only came to light years later from interviews with former NSU employees.

      The Flat-6 project ended up being canned because NSU management thought it to be undesirable, though it is unknown whether they thought the engine was undesirable compared to the potential benefits the rotary engine offered or because the Flat-6 was more akin to Citroen’s own shelved Flat-6 project. Either way it was a mistake for both to not limit the rotary engine to low volume sports-cars until it was ready for mass production, while collaborating with each other on conventional engines.

  10. It is interesting to note that Citroen looked at a 130 hp Twin-Cam 16v version of the 1987cc DS engine for a DS Sport project (which later became the SM and was apparently tested in a Panhard 24), makes one wonder what larger displacement versions would have been like as well as how much more power a Twin-Cam 16v version of the CX 2.5 GTi Turbo would have produced (along with a smaller 2-litre Twin-Cam 16v Turbo)? –

    It is also worth mentioning that Panhard wanted to use a 2-litre air-cooled Flat-4 possibly derived from the 90 hp 2-litre Panhard AML to power the Panhard 24, only for Citroen to refuse giving approval (along with 4-door saloon, 5-door estate and other Panhard 24 models).

    Since a higher compression version of the 90 hp 2-litre air-cooled Panhard Flat-4 would likely put out similar power to the Wankel engine used in NSU Ro80 and in the Citroen GS Birotor, it would have been fascinating to see Citroen make use of the 2-litre Flat-4 in other models or even for Panhard (under Citroen) to produce its own Flat-4 powered version of the NSU Ro80 as a replacement for the Panhard 24.

  11. As far as tax horsepower displacement limits are concerned, would France have benefited from regulations stating to the effect of 6-cylinders featuring a tax rate limit of 3-litres with any larger than a 6-cylinder being limited to 4-litres (later 5-litres) instead of 2.7-litres for all engines?

    1. Without a doubt. That single policy had a huge effect on France´s long-term ability to compete. I expect it was seen a s way to stop German and British cars competing against the French who were not so good at making large engines. It backfired enormously. I imagine the legislators were naive. Maybe the French car makers themselves didn´t see the effect of staying out of that engine size range. I guess they felt (not unreasonably) that light cars don´t need big engines and also that French tastes would always tend towards French-style cars.

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