(first posted 12/18/2015) By the end of the 1960s, automotive engineers realized it was necessary to control cylinder head temperatures to moderate emissions of NOx. And the EPA was mandating ever-tighter rules and regulations for air pollution. The air-cooled engine had to go.
But there were a few manufacturers who had built their reputations on air-cooled engines, and they continued to believe in them. Among them were Honda of Japan and Citroen of France. Within months of each other, in 1969 and 1970, they introduced brand-new cars with air-cooled engines designed from a clean sheet of paper. The cars they powered were small by American standards, but mid-size in their native countries. We’re talking about the Honda 1300 and Citroen GS.
Honda had been dabbling in microcars as a sideline to its fantastically-successful motorcycle business for a few years. But these were just a curiosity outside of Japan. Soichiro Honda, the founder and master of the Honda company, wanted to enter the big leagues. He wanted to manufacture a car that could be sold outside the home market in large numbers. Something that would compete with the Toyota Corona and Datsun Bluebird.
With the exception of a few water-cooled Formula 1 cars, Honda built nothing but air-cooled engines for its motorcycles and cars through the 1960s. Soichiro Honda loved air cooled engines. “Since water-cooled engines eventually use air to cool the water, we can implement air cooling from the very beginning,” professed Mr. Honda. And he wasn’t taking no for an answer, for he personally oversaw the engineering of the new 1300 automobile.
Offered as both a sedan and a sporty coupe, the new Honda 1300 bristled with innovations. It was one of the very few front wheel drive cars in its class. It had disk brakes in front and four wheel independent suspension. This was heady stuff for a Japanese manufacturer at that time. And of course, it featured an air-cooled engine, mounted transversely at the front of the car.
The fact that it was an inline air-cooled four cylinder engine was not remarkable. This had been done before. But the engine was nevertheless notable for two reasons. (1) the technology employed for cooling the engine was both strange and unique, and (2) it was ridiculously powerful for its size.
Soichiro Honda knew that a noisy engine would not be acceptable for a world class car. And air-cooled engines have a reputation for noise due to the resonances of their cooling fins and lack of water jackets to dampen miscellaneous vibrations. So he drove his engineers crazy with all kinds of ideas to overcome these problems.
Instead of relying on long, thin cooling fins, his engineers specified short stubby ones shaped with curves and waves to suppress harmonics. The blower fan had short blades for the same reason. But what really made the 1300 engine so unique is that the engine block had cast-in airflow jackets, rather than sheet metal shrouds, to direct the cooling air around the heads and cylinders. And the jackets were ribbed, internally, to further exchange heat with the cooling air.
If you look at the exterior of the block, you will see cooling fins. But these are not on the cylinder barrels or heads. They are on the exterior of the cooling jackets.
The castings were in aluminum, of course, and were intricate to the extreme. It must have cost Honda Motor Company a small fortune to build each one.
The 1300 was available in two series, the 77 Series with 100 horsepower; and the 99 Series offering 115 horsepower. That’s 115 horsepower from an engine with a displacement of only 1,300 cubic centimeters (79 cubic inches).
How in the world did they do it? Well, this was basically a little racing engine, with an overhead camshaft, four Keihin carburetors, hemispherical combustion chambers, and dry sump lubrication system. Peak power was delivered at 7,300 RPM. It combined all the best of Honda’s motorcycle and Formula 1 racing experience.
Soichiro Honda was entering his 60s during the design phase of the Honda 1300 and he evidently saw this project as his pièce de résistance. It was the last engineering project he would ever lead. He drove his engineering staff to near mutiny with design changes even after the production line started rolling. Working from 5 AM to midnight every day, some of the workers were suffering from sleep deprivation, even falling asleep in the men’s room.
So, if the Honda 1300 was such a master piece, why don’t we hear about it today?
There are several reasons. It was more expensive to buy than similar-size cars in Japan. It was more expensive to make than it was to buy. And for all its’ engineering innovation. the little air-cooled engine turned out to be heavier than expected. The car was hard to steer and hard on front tires.
The Honda 1300 was sold in several countries around the Pacific Rim, (most notably Australia and, of course Japan). But it never made it to Europe and the Americas.
In 1973, Honda replaced the 1300’s air-cooled engine with a water-cooled fuel-injected variant which held things over until the introduction of the wildly-successful Honda Civic. And that was the end of Honda’s foray into air-cooled engines for passenger cars.
Citroen occupied two segments of the market in Europe. At the top was the DS series, known for its advanced hydro-pneumatic suspension. The DS had sleek if somewhat strange styling which was considered quite sensational when it was introduced in 1955. Although they were front wheel drive, they were powered by conventional water-cooled engines.
But Citroen also had plenty of experience with air-cooled engines, too, for its entries at the bottom rung of the market had been around for a long, long time. Citroen introduced its 2CV series way back in 1948 as a “people’s car” for France and the slightly larger Ami had been around since 1961. Both were powered by tiny air-cooled two-cylinder boxer engines.
So, while Citroen had cars for rich and poor, it had nothing to offer for Europe’s middle class which was expanding fast in the mid-1960s. Other manufacturers, like Renault and Fiat were cashing in on this market segment. Citroen needed a contender and so the GS was born.
Citroen had a reputation for bucking convention in the 1960s, and the GS was no exception. Like its big brothers, the GS had hydro-pneumatic suspension for a soft cushy ride, front wheel drive, and aerodynamic styling. It also had four wheel disk brakes. But unlike the upscale DS, the GS had an air-cooled boxer engine, a nod to its smaller siblings. And what an interesting little motor it was!
It was only the size of a Volkswagen Beetle engine in terms of displacement, and like the Volkswagen, it was a four-cylinder engine. Anybody familiar with a Beetle or Corvair engine would immediately recognize the basic layout, with a split crankcase, individual cylinder barrels and bolt-on heads.
But the GS engine was more sophisticated. It had an overhead camshaft driven by a cogged belt for each cylinder bank. This allowed hemispherical combustion chambers with relatively large valves.
The cooling fan was mounted directly on the crankshaft, so their was no fan belt. The crank shaft was a built-up affair, which enabled the use of one-piece connecting rods and journal bearings for lighter rotating mass; the one piece rods eliminated the need for connecting rod caps and bolts.
A two-barrel Solex carburetor was used, mounted on a central manifold with four separate tubular runners to the cylinders, much like one of those after-market center-mount carb conversions that were marketed for Volkswagens and Corvairs.
Initially, the carb base was heated with engine oil to prevent icing, but this didn’t help much when the engine was cold, so Citroen replaced it with a setup that routed a bit of engine exhaust through the carb base.
These were small engines, and when introduced, displaced only 1,015 cubic centimeters. Citroen made them small for taxation purposes in France. Later, in the mid 1970s, they were bumped up to 1,129, 1,222, and 1,299 cc.
Power ranged from a mere 56 hp (DIN) to 66 hp, but the little engines revved happily at highway speeds and, according to anecdotal information, could easily be revved to 8,000 RPM with no damage.
You might be thinking that a car with such radical features would be a flop in the market, but Citroen built and sold 2,474,346 of its GS series cars between 1970 and 1986. But sadly, few remain on the road today. Although the engines were strong, the cars were not rust proofed very well and many simply rotted away!
The preceding article was inspired by End of an Era: The Last Air-Cooled Automobile Engines, by James Kraus. For a full list of references, please contact the author, Allan Lacki.