In the mid to late 1920s a number of luxury car manufacturers began work developing multicylinder engines. Not to be outdone, Cadillac began work on two different multicylinder engines, a V-12 and a V-16. Larry Fisher, Cadillac General Manager, leaked to the press information about the V-12, hoping to keep the V-16 a secret.
Owen Nacker, who designed the Cadillac V-16 engine, also designed the Cadillac V-12 engine,and it shared the tooling and many of the components of the V-16. The V-12 was essentially a truncated V-16, with a bore of 3.125" instead of 3", giving it a displacement of 368 cubic inches. It shared the V-16's 45 degree bank angle., rather than the 60 degree angle that would have been ideal. The V-12 was less powerful than the V-16, generating 135 versus 175 horsepower. Both engines featured overhead valves in the first generation.
Series 370 (1931-1935)
The 1931 Model 370A V-12 was introduced in October 1930. A V-12 roadster was used as the pace car at the Indianapolis 500. The Cadillac V-12 had a shorter wheelbase than the Cadillac V-16, with a choice of 140 in (3,556 mm) or 143 in (3,632 mm), compared to the V-16's 148 in (3,759 mm), but it offered a similar choice of Fisher and Fleetwood semi-custom bodies. It was difficult to tell a Cadillac V-12 from a Cadillac V-16 unless you were close enough to read the figure "12" mounted on the headlight tie bar, but the hood was four inches (102 mm) shorter, and the headlights and horns smaller than a V-16's. More significantly, the V-12 cost about $2,000 less for each bodystyle, starting at $3,795. The Cadillac V-12 might have been lower in prestige than the Cadillac V-16, but it joined a select group of 1930s cars with multicylinder engines, namely those manufactured by Franklin, Hispano-Suiza, Horch, Lagonda, Maybach, Packard, Rolls-Royce, Tatra, Voisin, Walter, Marmon and Lincoln. Moreover, thanks to its lower price, it immediately outsold the Cadillac V-16 with 5,733 sold in the 1931 model year, versus a mere 363 for the V-16.
The appearance of the 1932 Series 370B benefited from a radiator shell that flared on the top, more flaring fenders and curved running boards. Mechanical changes included a stiffer frame, and a Cuno self-cleaning oil filter mounted at the right hand side of the clutch housing. Dual Detroit Lubricator carburetors were used in place of the Cadillac/Johnson carburetors that had been standard equipment on Cadillacs for 20 years.Largely thanks to the deepening Great Depression sales plunged to 1740 units.
Styling changes to the 1933 Series 370C included a V-shaped grill that blended into the painted radiator shell, a radiator cap hidden under the hood, and skirts on the front and rear fenders for a more streamlined look. Fisher no-draft individually controlled vent windows were a new standard feature. Sales fell further to 953 cars.
The 1934 Series 370D was restyled yet again but this time was mounted on a completely new chassis. The radiator grill slanted rearward with a central bar and five horizontal sections, the windshield sloped even more rearward, headlights were enclosed in new teardrop housings mounted on streamlined supports, the horns joined the radiator cap under the hood, the spare tire was concealed under a new beaver tail deck on most models and the whole car sat approximately 2 inches (51 mm) lower. Significant mechanical advancements included dual X-frame chassis construction, "Knee-Action" front coil spring suspension that greatly reduced unsprung weight and Hotchkiss steering. The 1935 Series 370E saw the addition of the Fisher Turret Top on Fisher bodied cars and an increase in horsepower to 150. Sales over the two years combined totaled only 1098.
Series 80/85 (1936-1937)
The Cadillac V-12 was renamed the Series 80 and 85 in 1936. The Series 80 and 85 featured a 131" and 138" wheelbase respectively. All V-12s were now Fleetwood bodied and had Turret Tops. A total of 901 V-12s were sold in 1936.
In 1937 the Series 80 was dropped leaving only the long wheelbase Series 85. The only significant mechanical changes were the adoption of an oil-bath air cleaner and a pressure radiator cap. Sales were only 478.
Cadillac redesigned its V-8 and V-16 for the 1936 and 1938 model years respectively, so the question naturally arises, why did Cadillac allow the V-12 to expire after the 1937 model year? The new monobloc V-8 was stiffer mechanically and had more reliable seals than the preceding generation. Both the new V-8 and V-16 were more efficient in terms of horsepower per cubic inch than the preceding versions. One or both of these advantages could easily have been conferred on a replacement for the V-12. And, interestingly, the redesigned V-16 had side valves ("flathead" design) instead of the more modern OHV design featured on the original V-12 and V-16. Cadillac would not feature overhead valves in any of their engines again until 1949.
But sales for both the V-12 and V-16 had been poor due to the Great Depression. Furthermore, the horsepower gap between the V-8 and V-16, both arithmetically and geometrically, shrank with the introduction of the new generation of engines. It is likely that GM decided it could only afford to develop one multicylinder engine replacement, and that the one that distinguished itself most in terms of the number of cylinders, smoothness, quiet and power was the one that was worth the expense.
In any case the classic multicylinder era for American cars was drawing to a close. Packard ceased production of its V-12 in 1940 and Cadillac ceased production of the redesigned V-16 the following year. Only Lincoln's V-12 would last beyond WW II, and its production came to an end after the 1948 model year.
As part of the General Motors V-Future program, Cadillac had an overhead cam V-12 slated for production in the late 1960s. The program led to a fiberglass mockup of a V-12 powered Eldorado coupe that remained hidden from public view until an article appeared in Special Interest Autos in 1984.
Reports of new V-12 developments reappeared in the late 1980s. Cadillac showed the fully working Cadillac Solitaire concept in 1989, equipped with a Lotus-designed 6.6 liter DOHC 48-valve V-12 with multiport fuel injection.
A Northstar-based V-12 was featured in the Cadillac Cien concept car of 2001, and tested by Cadillac engineers as an engine for a Cadillac Escalade with somewhat improved performance. An AutoWeek report in 2007 claimed a V-12 in the design phase was to be based on the High Feature V6.
The Cadillac Sixteen concept utilized an all-aluminium pushrod V-16 engine based on the same architecture as GM's then-current small-block V-8 developments. A production version with a base V-8 and the option of the V-12 engine was planned, but was never approved for production and was ultimately shelved around 2008.