Honoring Burt Munro And Celebrating Speed On The Salt

Описание: The legacy of “The World’s Fastest Indian” returned to Bonneville 50 years after Burt Munro’s feat, this time with his grand-nephew Lee Munro piloting an Indian Scout produced by today’s Indian team.

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On the Bonneville Salt Flats you stand on a mirror of pure white that will burn your skin from below while the arc-welder sun burns from above. Dark jagged mountains surround it. But it’s flat. And big. A place to run for top speed.

In August of 1967, one-man R&D team Burt Munro, then 68 years old, streaked across that salt to set a 1000cc record of 183.586 mph in his home-built streamliner. It was powered by an engine that began as a 36.4-cu.-in 1920 Indian Scout that he'd bought new. With his own hands he had made the OHV heads, cylinders, pistons, connecting-rods and cams of his engine, working in a New Zealand shed that was his home for 27 years. He had set innumerable records with it. That was 50 years ago.

At the end of 2016 Burt Munro's son John and grand-nephew Lee Munro inquired from Indian in Minnesota whether they planned any commemoration of this historic achievement. The answer was, of course! In January 2017 came the go-ahead from the corporate president's office; a Scout-based Bonneville racer would be built and Lee Munro—a competitor in Australian Superbike—would ride it.

On Saturday, August 12, 2017, Lee Munro rode a modified modern Scout to 191.286 mph on the rough and slushy Bonneville short course, in the Modified Partial Streamlining (MPS) 1350-G class. This was not an attempt at a standing record. It was a practical recognition of Munro’s dedication to an ideal (his shelves of holed pistons and twisted con-rods bore the words “Offerings to the God of Speed”) and a renewed commitment to striving for excellence.

The Indian brand is more than 100 years old and the success of Polaris in reviving it is testimony to its power—so many riders and others today had a father or grandfather who rode Indian that the name is folk memory. How did management decide so easily to continue Munro’s Bonneville quest? Without continued striving and achievement, the memory would remain just a big shapeless bag of leftover sentiment.

The basis would be the Scout, whose engine is a liquid-cooled 60-degree V-twin of 99 x 73.6mm bore and stroke for 1133cc, with four valves per cylinder operated by chain DOHC. The limit of the Bonneville class chosen was 1350cc. To get closer to that a whacking great 7mm overbore took the cylinders to 106mm and displacement to 1299cc (79.3 cu.-in).

This is a cruiser engine, right? So what's it doing with a sportbike's four valves and double overhead cams? In two-valve cruiser engines the key to mighty bottom-end torque is short valve timing, but as they rev up, that short timing limits airflow, causing torque to slope down with rising rpm until they wheeze out at around 5,000 rpm. But what if you've ridden other kinds of bikes and like that feeling of winged power that sails without strain to higher revs and real horsepower? The only way to combine the short timing that makes torque down low with enough airflow for power up higher is with a very light four-valve-per-cylinder valve train. That is the essence of Indian's Scout—it has it all.

When you plan for Bonneville you need several things. One is power—the power to overcome aero drag that rises as the cube of velocity. Another is reliability—too many teams "go to blow" because their powerplants are fragile at the necessary power level. After the fact it's romantic to remember all-nighters spent under the stars in the glare of headlights, putting another $10,000 worth of parts into a blown engine. Better by far to have an engine that does what you need it to do easily. The last biggie is traction. Even at the best of times grip on the salt is maybe 40 percent of what it is on nearby Interstate 80. It can also be wet, slushy, and rough. Then there are details like streamlining, or making sure your electrics aren't shorted by the salt that has caused so many efforts to sput out.

The stated aim of the Indian crew was to honor Burt Munro and say “We’re here!” but I have a suspicion that what they really wanted was to hit 201 mph.

Horsepower. First was more displacement—the 7mm overbore. There’s no point in going big if you can’t deliver the necessary extra airflow. The obvious path was bigger valves (intakes are now 42mm, exhausts 36) but the valve guide locations correct for a 99 bore were too close together for bigger valves (crowd them and cylinder heads crack between the two exhaust seats or from plug hole to exhaust—unless there’s enough metal between).

Full story here: https://www.cycleworld.com/honoring-b...

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