Leon Duray’s entry in the 1931 Indy 500—a supercharged, 16-cylinder two-stroke—was a complete failure, but that doesn’t make it one bit less fascinating. Join us for a closer look at one of the most unusual racing engines ever built.
Leon Duray was one of the great personalities of the early years of American auto racing. A Detroit cab driver turned racer whose birth name was George Stewart, Duray set a qualifying record at Indianapolis in his front-drive Miller in 1928 that stood until 1937. For the 1931 race, Duray brought a new race car powered by one of the strangest engines ever seen at the Brickyard: a supercharged, 16-cylinder two-stroke. Let’s dive right in for a closer inspection.
Actually, Duray brought two matching race cars to Indy for 1931, one for himself and one for his financial backer and co-driver Cliff Durant, but only Duray’s mount was ready in time to qualify for the race. Built to exploit a provision in the Speedway’s rules that allowed supercharging without penalty on two-stroke engines, the Duray employed a giant Roots blower (above) driven from the front of the crankshaft, feeding the 16 cylinders through a fan-shaped, intercooler-type intake manifold and a single Winfield carburetor.
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The Duray’s 16 cylinders were arranged in side-by-side pairs, with each pair sharing a common combustion chamber and crankshaft journal—that is, 16 cylinders with 8 chambers and 8 crank throws. First patented in 1912 and known in Europe at the time as the Zoller (after engineer Arnold Zoller) two-stroke, in more recent times this general layout has been called a split-single or “twingle,” as used on small-displacement European motorcycles (DKW, Puch et. al.) well into the 1960s. On the Duray 16, each cylinder was of 2.438-inch bore and 3.250-in. stroke, yielding a total displacement of 242.7 cubic inches.
This view of the right side of the engine permits a better look at the four individually cast aluminum cylinder blocks, each one housing two pairs of cylinders and bolted to a common crankcase, also aluminum. The intake charge entered the left cylinders and spent exhaust gas exited on the right; with the header pipes removed, the wide, flat exhaust ports can be seen. Each chamber employed two spark plugs, fed by two Bosch eight-cylinder magnetos, one on each side of the engine.
Contemporary track reports in Motor and elsewhere assert that the Duray U16 was the fastest machine on the bricks in 1931, and the loudest as well, with a piercing scream that turned heads all around the track. However, the engine was plagued with overheating issues, with both the water pump and jacketing called into question, and couldn’t put together more than a few laps at a time without boiling over or seizing. Duray managed to qualify the beast at 103.134 mph, a quite respectable speed, but on race day traveled only six laps before the engine failed again, producing a 37th-place finish. As fast as it was, and as loud as it was, the U16 was a failure.
Shown here in the cockpit of the U16 are driver Leon Duray and riding mechanic L.H. Miller. Standing just to the right of Miller are the cigar-chewing racing legend Barney Oldfield, and to his left, Speedway manager T.E. “Pop” Myers. The 1931 race would mark Duray’s final Indy 500 as a driver, but he would continue his career as a successful team owner.
While the U16 engines were a flop, the chassis created to house them enjoyed better success. Constructed for Duray by famed California builder Myron Stevens, the two race cars employed Willys-Overland Whippet chassis and components combined with Model A Ford transmissions and rear axles. When the troubled two-stroke engines were removed and conventional Miller fours were installed, at least one of the chassis was competitive at Indy and elsewhere for several years.
For the 1932 500-mile sweepstakes, Duray returned to the Speedway one more time with a revamped U16 with the big Roots blower relocated to the rear of the engine and a Stromberg carburetor replacing the Winfield. However, the overheating problems were never overcome and in its final appearance, the Duray failed to qualify.
-Indianapolis Motor Speedway photos.
Outstanding! I’ve always wanted to know more about this crazy engine. Some books give it only a tease.
Don’t know where you find all the info. you provide us with, nor where you find the time to find the info., but I find it very interesting, entertaining and informative.
At the end of this, you’ll find my thanks for all your effort! It’s appreciated!
I wonder why the overheating problem couldn’t be resolved. Two cycle motorcycle racers use air cooled 2 stroke engines without issues routinely. As a side note Famed NASCAR/Indy mechanic envisioned and worked on a concept to use 4 MC 30 2-cycle engines at Indy. The concept was to use one engine to drive each wheel independently in an AWD configuration. He acquired the engines and worked on increasing the power from the engines but stopped short of building the racer. Considering the layout of Indy and the high RPMs of a two stroke engine it seems like an ingenious concept. Due to today’s Indy Spec racing rules we will never know if this or any other innovative concepts would have been proven or disproven. That the sad aspect of Indy and racing in general today.
Cold intake air enters the left side cylinders and hot exhaust gas exits on the right side cylinders. This would create extremely uneven cooling and make the engine basically try to break itself in half.
Great story! As a teenager my dad had a Sears Allstate brand motorcycle with a single/twin engine like this. It sat in our garage until one day a collector came and bought it. Dad drew pictures of the engine operation for me.
Great story! I really wish I could have heard it run.
Thanks for keeping American Automotive History Alive! Barney Oldfield, Master Driver of the World & America’s Legendary Speed King Great Great Nephew
as a young man I owned a sears allstate 106! ordered out of the cataloge the 2 stroke sound was unlike anything most people had ever heard. It blew up due to overheating and was scrapped due to lack of replacement parts. I can empathize with there frustration!
I find this kind of engineering excercise very interesting. The mechanical genius is amazing even in failed designs and is much more interesting than the invisable wizardry of aerodynamicist. Indeed this is what is missing from Indy today.