1934 Harley-Davidson CAC Racer: Harley’s Factory Speedway Experiment
The 1934 Harley-Davidson CAC was a short-lived factory speedway racer built for a corner of American competition that Harley did not usually own. On cinder tracks, where riders pitched brakeless singles sideways through loose black grit, British JAP and Rudge machines had become the bikes to beat. Harley-Davidson’s answer was the CAC: a rare 500cc single-cylinder racer tied closely to Joe Petrali, alcohol fuel, direct drive, and one of the strangest one-year experiments in the company’s racing history.
On cinder tracks, the CAC put Harley-Davidson into a specialized corner of vintage motorcycle racing where lightweight foreign singles had already set the standard. It was an unusual factory experiment, and it shows how far Harley-Davidson was willing to go when it briefly chased a racing format dominated by British machines.
Why Harley Built a Speedway Racer
Speedway racing was growing quickly in the United States during the early 1930s. Unlike the wooden banking of the earlier board-track era, the tracks were covered with fine cinders, a byproduct of coal-fired plants, and the motorcycles used there were stripped down for acceleration and slide control rather than road use. The best machines were often lightweight British singles, especially JAP-powered racers and Rudge machines, and that British dominance stood out to Harley-Davidson factory racer Joe Petrali.
Accounts of the CAC usually put Petrali near the center of the project. One version says Harley-Davidson management had limited interest in building a dedicated speedway machine, so Petrali and a few factory people worked on the bike around the edges of normal factory business. Another version gives more credit to the racing department as a small engineering effort. Either way, the result appeared in 1934 as a purpose-built Harley-Davidson cinder-track racer, not a converted road model and not the kind of earlier factory racing hardware Harley riders already knew.
The timing is interesting. Earlier factory-racing landmarks such as Dodge City had helped define American motorcycle competition, but by 1934 racing was moving toward AMA Class C rules, with production-based 45 cubic-inch side-valve machines on gasoline. The CAC went in a very different direction. It was a specialized speedway bike, built for a narrow job, with a high-compression single-cylinder engine and no street equipment at all.
The CAC Engine and Direct-Drive Layout
The CAC used a 500cc single-cylinder engine that borrowed heavily from British speedway thinking. It is usually described as a JAP-style design, with very high compression and alcohol fuel. The commonly repeated compression figure is 16.5:1, an extreme number for the period and one that only makes sense in a racing context. The engine was said to turn about 6,000 rpm, and the whole motorcycle was built around the idea of getting that power to the rear wheel with as little loss and delay as possible.
There was no transmission and no clutch. The crank drove through a short-coupled jackshaft and chain straight to the rear wheel, making the CAC a pure direct-drive speedway racer. That layout made the bike simple and light, but it also made it specialized. It was not a motorcycle you could ride around, shift through gears, or slow down with normal controls. It was built to launch, slide, and keep moving.
The CAC also had no brakes. That sounds reckless if judged as a road motorcycle, but it was normal for speedway work. Riders controlled speed with throttle, engine drag, line choice, and the controlled slide. The bike’s lack of brakes, clutch, and gearbox was not an oversight. It was the point.
How Many CAC Racers Were Built?
The production total is one of the long-running questions around the CAC. Harley-Davidson claimed 20 complete racers and five spare engines. Many later sources put the number of complete motorcycles closer to 12. With a machine this rare, both numbers matter: one reflects Harley’s own claim, while the other reflects the much smaller count often repeated by collectors and historians.
The survivor count is just as uncertain. Older accounts have placed the known-survivor number at about nine, while auction and collector summaries sometimes use a broader 9-to-12 range. Either way, the CAC sits among the rarest Harley-Davidson factory racing machines. Public documentation is thin, and much of what is known comes from auction listings, private collections, surviving engine numbers, and the few machines that have surfaced in public view.
One documented auction example, offered at Mecum Las Vegas in 2020, was described as a 1934 Harley-Davidson CAC Speedway in original condition. Its number was listed as XX2040. Another known CAC engine has been photo-documented with a 34CAC503-style number. The exact meaning of those prefixes is still not something I would treat as settled from public evidence alone, but they do show that these bikes lived in a special factory racing-number world, not the ordinary production numbering readers expect from street Harleys.
Harley’s Press Release Sounded Confident
Harley-Davidson’s own press language made the CAC sound like a serious contender. The company described the new short-track racers this way:
“The short track racers we are offering are the result of much study and actual trial by our racing department. Extensive tests were conducted on the West Coast on actual tracks with outstanding short track racing stars and in competition with the best of the foreign machines. Our experimental machines came through every test with flying colors. Improvements incorporated as a result of these trials will make these new racing models even better in power and performance.”
That is not the kind of announcement you expect for a motorcycle that disappears almost immediately, but that is what happened. The CAC did not become a familiar Harley-Davidson racing platform. There are no widely known race results or victory records that put the bike into the same conversation as Petrali’s more successful Harley racers. The program appears to have faded before the machine built a public competition record.
Why the CAC Disappeared
The reasons for the CAC’s quick disappearance are still partly rumor and partly inference. The usual rumors include camshaft trouble, timing problems, and disappointing performance. The bike may also have suffered from the same problem that makes it fascinating today: it was extremely specialized. Harley-Davidson was trying to build a high-strung, alcohol-fueled, direct-drive speedway single at a time when its American racing future was moving toward other formats and other machines.
Petrali himself did not need the CAC to prove anything. His career remained tied to more successful Harley-Davidson racing machines, including the streamlined Knucklehead which set Harley's first land-speed record. The CAC, by comparison, became a one-year factory experiment: bold enough to show that Harley knew exactly what the British machines were doing, but not successful enough to earn a lasting place in the lineup.
A Rare Harley-Davidson What-If
The CAC is one of those motorcycles that raises more questions than it answers, much like Indian's later fully enclosed Arrow streamliner. Was the CAC mostly Petrali pushing Harley into a sport the company did not really want to chase? Was it a legitimate factory racing department project that simply missed the mark? Did the mechanical problems kill it, or did Harley-Davidson decide the speedway market was too small to justify the effort?
What survives is a very rare factory racing machine with a clear purpose and a short paper trail: 500cc, high compression, alcohol fuel, direct drive, no clutch, no gearbox, no brakes, and a production total that may have been closer to a dozen than Harley’s own larger claim. For a company better known for big V-twins, the CAC is an odd little detour into the world of cinder-track singles.
I would still like to see one sliding sideways through a corner on a cinder track.