Simanaitis Says

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I LIKE COMPLEX POWERPLANTS. The W-12 Napier Lion, for instance, is a trio of four cylinders arranged broad-arrow fashion and powering the Napier-Railton. Another is even more elaborate: the Duesenberg W-24, as described by Dean Batchelor in R&T, August 1992. Here are tidbits gleaned from Dean’s article and from William Pearce’s 2013 analysis of the Duesenberg W-24 in Old Machine Press. 

A Marine Engine, Dodge Cash, Duesenberg and Miller Expertise. Whereas the Napier Lion had aero heritage, the Duesenberg W-24 was designed to power a racing boat. Dean described, “… it was in late 1925, when Horace Elgin Dodge, heir to a fortune created by Dodge cars, approached the Duesenberg brothers, Fred and August, to design for him an engine capable of beating anything afloat.”

The resulting powerplant, Dean wrote, “has to rank as one of the most impressive engineering exercises of internal combustion engine building. It has 24 cylinders in a ‘W’ arrangement; for all practical purposes it was three straight-8 engines with a common crankcase and crankshaft.”

What’s more, each straight-8 was fundamentally a pair of abutted four-cylinder blocks, with typical Duesenberg Indianapolis practice prevailing: double overhead camshafts actuating four valves per cylinder with pentroof combustion chamber.

The complex gear-drive arrangement for the camshafts at the rear of the 24-cylinder Duesenberg. This and other images from Old Machine Press.

Pearce noted at Old Machine Press: “The pinion on the crankshaft had 17 teeth, the intermediate gears had 74 teeth, and the camshaft gears had 34 teeth, The center intermediate gear engaged an idler gear that had 45 teeth. The gearing drove the camshafts at half engine speed.” 


Tripled Complexity. When tripled, note, engine characteristics resulted in a total of 96 intake and exhaust valves actuated by six camshafts, with air and fuel attempting to reach 24 cylinders in banked angles of 60 degree, 24 spark plugs timed to initiate combustion, and 30 exhaust pipes tuned to handle the residue. 

Why 30?? You’d expect either 24 largish pipes (one per cylinder) or 48 tiny ones (with each dedicated to its own exhaust valve). But, as Dean noted, “Each of the 4-cylinder blocks was designed with four intake ports and five exhaust ports.”

This was a compromise of exhaust flow and packaging. Dean described the solution: “… provide a single exhaust port and pipe for the end exhaust valves in each block (valve numbers 1, 8, 9, and 16 on each bank. Cylinders two and three, and six and seven (valves numbered 2-3, 4-5, 6-7, and 10-11, 12-13, 14-15) share ports and pipes.”

Above, the surviving Duesenberg W-24 as seen in 1996. Image by Pat O’Conner from Old Machine Press. Below, my sketch of one bank’s exhaust pipes and porting.

Bring on the Blower. J. Paul Miller (not to be confused with another engine wizard Harry Miller) was later retained to reengineer aspects of the design, though its basic configuration remained. A crucial addition was Miller’s applying centrifugal supercharging. Operating at 6.5 times engine speed (32,500 at the engine’s 5000-rpm redline), the blower produced a boost of 15 psi. (1.03 bar).

Two twin-barrel carburetors feed the supercharger. A trio of Bosch magnetos are driven by the camshafts. 

Dean observed, “Apparently, the basic problem with the engine, prior to the addition of the supercharger, was fuel distribution. Miller designed new intake manifolds when he designed the blower, and this combination solved their problems.”

Image by Drew Motta (Art Director Wm A.’s son) from R&T, August 1992. 

“It also added considerable horsepower,” Dean noted. “In its final stage of tune with the supercharger, the W-24 achieved a reliable 845 horsepower at 5000 rpm.”

Above, the W-24 is installed into the racing boat Notre Dame. Below, the pilot and mechanic surely got the full sound and fury.

William Pearce wrote, “Reportedly, at full song the engine produced a sound like nothing else on earth.” Dean Batchelor quoted Dan Arena, the Notre Dame’s pilot, saying it sounded like “a field of Offy midgets starting a race at Gilmore Stadium.” ds 

© Dennis Simanaitis,, 2021 

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