What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach?

What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach?

      RM Sotheby's

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      This year's Best of Show award at the 2025 Pebble Beach Concours d’Elegance went to a 1924 Hispano-Suiza H6C Nieuport-Astra Torpedo, presented on Sunday. The vehicle certainly stands out when compared to modern cars, particularly due to its oddly shaped exhaust, which immediately captured my attention. I conducted some research to uncover its details.

      For some context: The car was initially commissioned and owned by André Dubonnet, a remarkable individual known for being a distinguished aviator, Olympic athlete, racing driver, and designer of car suspensions. His grandfather created the apéritif brand associated with his name, and he was involved in creating several one-of-a-kind vehicles. This specific automobile raced in the Targa Florio and Coppa Florio before becoming a sought-after collectible. It sold for $9,245,000 in 2022, after which its current owners, Penny and Lee Anderson, had it restored to its original specifications, undoubtedly at a staggering cost.

      Referred to as the “Tulipwood” Torpedo, the vehicle is actually made of mahogany strips, each meticulously carved and affixed to the inner framework using 8,500 rivets. According to the Pebble Beach show’s press release, it initially weighed just 160 pounds. The release included a statement from Mr. Anderson explaining his attraction to the car: "I like wood! I’m a collector of antique wooden boats. I began my collection 40 years ago, long before it became fashionable. I’ve always admired varnished wood, and when I first saw this, I thought, my goodness! This perfectly fits my interests. This is exactly what I love."

      That sounds delightful! Now, let’s address the exhaust. What is the deal with that unusual shape?

      As you can observe, the exhaust exits from the left side of the car before passing through a complex double-triangle-like maze that ends before the rear wheel. A closer look at images from the event reveals “Steigboy” branding, referring to Steigboy Apparatebau, established by Friedrich August Boysen in 1921. His Leipzig-based company manufactured vacuum exhaust systems mainly for motorcycles and some aircraft, and evidently, they also produced at least one automotive application.

      What we are examining here is an early vacuum muffler, sometimes known as an ejector muffler. The large, round sections resembling hamburgers are designed to create a substantial expansion of volume right after the header. This abrupt volume change aims to reduce sharp pressure pulses before they exit. In simpler terms, it acts as a reactive silencer based on volume and geometry, unlike the modern exhausts which use fibrous packing.

      According to German documents regarding the Vacuum-Auspuff from its inception, the muffler contains a beveled baffle opposite the outlet, with the outlet pipe featuring helical vanes. This configuration is meant to swirl and accelerate gas flow as it exits, creating a slight vacuum in the main chamber. The intended effect was to scavenge cylinders between pulses and minimize back-pressure while still muffling noise.

      This explanation is a rough approximation, but it reflects the functionalities inside Steigboy mufflers based on the patents and information I’ve been reviewing this morning.

      The round sections of the Steigboy are designed to optimize the volume-to-surface ratio and ensure symmetric wave reflections for pulse cancellation. The short neck needs to be at a right angle to the inlet to effectively deflect and redirect pulses and accommodate the spiral vanes. The overall “spheres with spout” design is essentially the smallest achievable packaging from the 1920s.

      At least, that was the theory given the measurement methods of the 1920s. Since this design didn’t last long, its practical effectiveness seemed to have been limited.

      In 1922, Boysen’s exhaust systems featured on the winning motorcycles at that year’s AVUS race, a fact the company prominently highlighted in their period advertisements. It appears that the 1920s were the pinnacle for the Steigboy brand; they also explored other transportation avenues, including creating a three-wheeled cargo truck.

      Eventually, the company evolved into The Boysen Group, which continues to produce exhaust systems alongside battery cases, hydrogen tank systems, control elements, electronic components, and other industrial products.

      It's fascinating to see such an exhaust system on a car, and it fittingly complements Dubonnet’s Nieuport-Astra-bodied Hispano-Suiza. Boysen himself had connections to aviation, and his silencers were marketed for cars, motorcycles, and aircraft, aligning the Steigboy technology and design perfectly with the theme and era of a gentleman aviator’s racing car.

      Overall, it’s a remarkably intriguing vehicle. Pebble’s judges made an excellent choice.

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What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach? What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach? What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach? What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach? What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach? What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach?

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What’s Going On With the Unusual Exhaust on the Best of Show Car at Pebble Beach?

The winner of the 2025 Pebble Beach concours was a 1924 Hispano-Suiza H6C Nieuport-Astra Torpedo, which features its distinctive exhaust design. I discovered the reasons behind its unique appearance.