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ALFA ROMEO P3—A CAR OF WINNING ECCENTRICITIES
WHAT MAKES the Alfa Romeo P3 such a fascinating study are the car’s Vittorio Jano-designed eccentricities, its Enzo Ferrari refinements, some effective, others bizarre, and its competitive longevity. This factory-entered Grand Prix race car during the period 1932 – 1935 goes by several names: the P3, the Tipo B and, befitting its single-seat configuration, the Monoposto. (Other Alfas of the era often had dual use, sports car or single-seat).
Tazio Nuvolari piloted a P3 to victory in its first outing, the 1932 Italian Grand Prix at Monza. That year, P3s also won the French, German and Monza GPs, as well as the Coppas Ciano, Acerbo and Principe de Piemonte. After a year’s hiatus for reasons of corporate finances, P3s were even more unbeatable in the 1934 season; among them, an innovative aerodynamic variant won that year’s race at Berlin’s high-speed Avus circuit.
An aerodynamic P3 won at Avus in 1934. Image from historicautopro.com.
In 1935, Nuvolari and the P3 gave Alfa (and Italy) a stunning upset to the German Silberpfeile, the Third-Reich-supported Silver Arrows of Auto Union and Mercedes-Benz, in the German Grand Prix at the Nürburgring.
Tazio Nuvolari and his Alfa P3 win the 1935 German Grand Prix. This and other images from Cars in Profile: Collection 1, Profile Publications, 1973.
As late as 1939, another P3 placed 15th at the Indianapolis 500 and then went on to win the road race at the New York World’s Fair. And, even after World War II, a pair of P3s, entered by Los Angeles TV pioneer Don Lee, made the grid again at Indy.
The 1939 World’s Fair-winning P3. Louis Tomei and the car finished 15th (some sources have them 12th) in the 1939 Indianapolis 500.
Eccentricities? How about the car’s unorthodox means of getting power to its rear wheels: The P3’s differential was mounted directly behind its gearbox, and twin driveshafts angled aft to bevel gears at each rear wheel.
Alfa Romeo P3, 1932. Cutaway by L.C. Cresswell.
Several benefits were claimed for this oddity of drive. The relocated differential, a heavy component, contributed very little to unsprung weight; this, to the benefit of handling on rough roads. The driver’s seat could be nestled between the vee, thus enhancing a low center of gravity. And rear axle weight was reduced by swapping the differential for the twin bevel sets and short half-shafts to the wheels.
Modern engineers have questioned Jano’s wisdom in this. Actual weight reductions, for example, were minimal. However, the P3’s racing record speaks with even more authority.
Its 2.9-liter eight-cylinder engine had the oddity of being two inline-fours, with power and auxiliary drive taken from their central mating. A benefit of this was eliminating the inherent whippy nature of an inline-eight’s long crankshaft. Two decades later, efficacy of the concept was repeated in the engines of Mercedes-Benz’s all-conquering W196 Grand Prix and 300SLR sports cars.
Alfa P3 2.6-liter twin-supercharged inline-eight. Cutaway by L.C. Cresswell.
The Alfa engine featured double overhead camshafts and twin Roots-type superchargers, each feeding a separate carburetor with 10-psi boost. The engine’s earliest variant produced 215 hp. Oddly, twin tachometers were fitted, despite the ignition system relying on a single Marelli magneto.
Which reminds me of another P3 variant that required dual tachs, the 1935 Bimotore. This brainchild of Enzo Ferrari, whose Scuderia managed Alfa’s racing, had two P3 engines, one in front, the other at the rear. Bizarrely enough, both drove the rear wheels, the front one through the “conventional” P3 twin-driveshafts arrangement.
Alfa P3 Bimotore, 1934. Image from Motor, August 4, 1973.
Alas, the Bimotore was thirsty, a tire eater and a beast to handle. On the other hand, Enzo Ferrari’s idea of converting the P3’s rod-operated mechanical brakes to hydraulic operation in 1935 was a good one. Also, that year’s larger displacement of 3822 cc raised output to 330 hp and was welcomed against the twin onslaughts of Auto Union and Mercedes-Benz.
In its original form, the P3 had a solid front axle, but another 1935 innovation brought it independent front suspension. Even here, though, unorthodoxy prevailed with a Dubonnet configuration.
A 1935 P3 fitted with Dubonnet independent front suspension.
Andre Dubonnet, heir to the Dubonnet vermouth fortune, invented this odd trailing-arm suspension perched at the ends of what appeared to be a traditional solid front axle. The hubs rode on the trailing links, their springs and damping encased in oil chambers connected to the axle. It was a clever form of independent front suspension, but suffered when these chambers leaked.
A basic Dubonnet suspension. Image from Zuckerfabrik24.de.
Other applications of Dubonnet’s concept included his own Hispano-Suiza H6C Xenia and Chevrolet’s Knee-Action Ride, also in the mid-1930s. Check out GM’s “Take It Easy” for a somewhat rambling description of Dubonnet benefits; at 7:28 of the video, there’s a great example of “Don’t try this at home, kids. We’re professionals.”
Peter Giddings and his P3, Monterey, 2010. Image by Bill Wagenblatt at petergiddings.com.
Variants of Alfa’s P3/Tipo B/Monoposto are still active in vintage racing, complete with their wonderfully throaty exhaust notes, their eccentricities and their winning ways. ds
© Dennis Simanaitis, SimanatisSays.com, 2015
Simanaitis Says 
In August 2010 I roused myself early enough to make it from Culver City to Bixby Bridge as the Tour d’Elegance passed before my camera. There are no facilities at the bridge so I had to leave before all the cars had passed. Just by luck, I pulled onto US1 behind Don Lee’s P3 number 42, and was treated to the blat of its unmuffled exhaust as the driver struggled to avoid stalling while preserving the clutch on the frequent slow uphill sections. I was tempted to leave my windshield forever smudged by the residue of what I assume was Castrol R.