The 18/23 h.p. Voisin
Alec Ulmann had an interesting article in The Bulb Horn, official organ of the VMC of America, last June, about the extraordinary performance of the 4-litre 18 c.v. Voisin. A good deal has been written in recent times about Gabriel Voisin and he wrote his own two autobiographies, notably “Mes Mille et une Voitures”, which someone should publish in English. But what Ulmann set out to do was to underline how very efficient the Knight double-sleeve valve engine of this 1920 Voisin was, due to the use of lightweight sleeves with very large “windows”, aluminium pistons, an engine speed of 3,900 r.p.m. made possible by using a rigid, five-bearing crankshaft balanced statically and dynamically, and the very high compression-ratio of 8½:1 at a time before anti-knock fuels such as ethyl leaded petrol were available.
Ulmann dismisses those who say Voisin merely copied the same-size Panhard-Levassor engine, of which he apparently had the specifications when he was embarking on post-war car manufacture, in the big hangars of his aeroplane factory at Issy-les-Mulineux. But he admits that Artault and Dufresne, from Panhard’s, helped Voisin. Ulmann touches on some of the competition successes of this production 18/23 h.p. Voisin, such as finishing 1, 2, 3, 5 in the 1922 GP de Tourisme at Strasbourg with specially streamlined sports four-seaters, thus humbling the Peugeots, which were 4th and 6th. He also says that one of these Voisins had beaten the “Blue Train” when driven by Lamberjack, over war-torn roads and the crossing of the Alps Maritimes, by a matter of six hours. This is new to me and impressive when one remembers that the Rover Speed-Six that did this in 1930 was only some 20 minutes faster than the Express and a modern Rover 2600 which repeated the performance this year (Motor Sport, page 307), had about the same margin in hand. Ulmann does not remind us that when it comes to the 24-hour record at Montlhéry, Bentley was superior to Voisin!
Ulmann says that the c.r. of the Voisin engine was reduced for competition appearances to 8.0:1, to give it a greater safety-factory. It developed, with the 8.5:1 c.r., he says, no less than 37 b.h.p.-per-litre. How does Mr. Ulmann arrive at this figure? He makes it plain that he is not relying on conjecture, magazine reports, or doubtful historical data. No, for in about 1927, he purchased from the New York Voisin agent, Mon. Berdoulai, at his premises on 59th Street, a much-abused 18/23 h.p. Voisin which had been traded-in against a new six-cylinder model. Ulmann spent the winter overhauling the car and cleaning out the mass of carbon from its ports. He then, as part of his Master Thesis for his post-graduate course in the MIT engine-laboratory under Prof. Dean A. Fales, managed to have the engine from his own Voisin tested on the Aero-Engine Laboratory’s Sprague General Electric dynamometer, under the Professor’s supervision.
This confirmed the claim, Ulmann says, of 37 b.h.p.-per-litre from the 4-litre Voisin engine. He reminds us that Voisin’s clients for these fine cars ranged from the then-French President, Alexandre Millerand, to Rudolf Valentino, as well as the Royal Families of Scandinavia, Holland and Rumania, and members of the Almanac de Gotha. He puts the b.h.p.-per-litre of the Voisin cars with the lowered c.r. at 30. Ulmann has “come clean” over his former criticism of W. O. Bentley and the BR rotary aero-engines (see “Vintage Postbag” in this issue) but cannot resist a further dig at him over this high-efficiency of the Voisin, for he compares the 3-litre Bentley’s b.h.p./litre figure of 23.36 and that of the 4½-litre Bentley of 26.6 b.h.p., with the 30/37 b.h.p./litre of the French engines, using Georgano’s published outputs for the vintage Bentleys. Ulmann remarks that he presumes he will get a loud “foul” from his friends in the BDC. . . . — W.B.