The annals of history contain plenty of strange designs created by teams working around the rules in the pursuit of speed. To me, the Honda NR750 has to be one of the coolest instances of racing the rulebook, as Honda eschewed over 100 years of development in piston engines and went oval—all because it was combustion-chamber count that mattered, not displacement.
If you’ve never gotten to ride one of these wild machines, now may be your chance. Iconic Motorbike Auctions is auctioning off a 1992 model with 3293 miles, and you’ve got until Friday at 11 a.m. PT to place a bid. What exactly is this bike’s story, you ask? Let’s dive in.
The unusual engineering exercise stemmed from Honda’s desire to stay with a four-stroke engine design rather than switch to the two-stroke design that was popular in Grand Prix racing during the 1980s. The original idea was to increase the cylinder count to eight, arranged in a tidy V, but the rulebook put the kabosh on that by capping the number of combustion chambers at four. Rather than scrap the design, Honda pivoted.
Engineers elongated and connected the cylinders, creating oval-shaped chambers—but only four of them. The oval pistons connect to the crankshaft by eight connecting rods, and the cylinder head holds eight valves per cylinder.
The incredible complexity of the design meant that the engine took longer than expected to reach its potential, and even when it lived up to Honda’s power goals, the bike wasn’t a particularly winning machine. The racing program shifted the NR name onto a two-stroke engine, leaving the oval-piston design as a footnote in the history of Honda’s GP racing program.
Then, in 1992, a crop of street machines finally featured the oval-piston design. Freed from the 500cc GP engine displacement cap, the NR750 boasted a more street-friendly 750cc displacement and produced 125 hp at 14,000 rpm. Thought the engine made five fewer hp and redlined 6000 rpm below the 500cc race version, reliability issues still plagued the design. Most of the 1992 models got tucked away as collector pieces, which is why from time to time great low-mileage examples, such as the one above, come to market. If you are an engineer nerd that loves two-wheeled machines, the NR750 might be just the bike for you.