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).
Another problem: stock intake ports. They look as though Keith Duckworth (honored Father of intake downdraft) began to draw modern ports but had to take a phone call. While he was out of the room, somebody else decided, “We need to put a single throttle body in the cylinder Vee to feed both, so we’ll just bend these ports horizontal…”
As the late Heavy Chief of airflow, Kenny Augustine, liked to say, “Air can either go fast or go around corners. But it won’t do both.” That meant Indian’s engineering team needed to not only relocate valves but straighten new intake ports. How about we just do new heads?
Those engineers created this project on their own time. When I asked how they all happened to volunteer, I was told, “How often do you get the chance to do a project like this using the latest research equipment? AVL cylinder pressure indicators, instrumented dynos, sensors…?”
Okay, I get it. This meant that those intake ports weren’t just draftsman’s art. They were also known in detail through simulation and measurement. MoTeC engineer James Whisler talked about the subtle effects of long verss short fuel injector duty cycle and how either is affected by injection timing. The more you can measure, the more potential control strategies you discover.
“You don’t want to spray the fuel on the port wall because so much will evaporate that the resulting vapor displaces some of the airflow,” he said.
You can’t say that unless you can actually measure and understand what’s going on. A twin-bore downdraft (Ford) throttle body completed the intake side. A single showerhead injector? Mm, maybe not; high flow operation is good but snap response? Not so good. So a single injector was added under each butterfly.
The result at this point is 175 hp at 9,100 rpm, with peak torque down at 7,300. They talked about their torque curve—a table, flat from edge to edge, just like the torque of Indian’s FTR750 flat-tracker. That is made possible by moderate valve timings, four valves, and large valve lifts. Plenty of torque down low because short timings prevent intake backflow. Torque continues to high revs because there’s plenty of airflow cross-section.
When the engine was warmed up on Saturday, its stable, regular idle told my ears that valve timing is not “Top-End-Only Bonneville Super-Stomp.” I would hear plenty of radical rumpity-rump idle from the two-valve V-8s warming up around us. All the contrasting sounds and what they tell are just another reason to be on the salt.
Low grip on salt means getting to full throttle takes time. I watched more than one supercharged roadster get to second gear, show white behind the right rear tire, then snap sideways an instant later, forcing the driver to lift. A 400-mph ‘liner paradoxically became much louder the farther it went away from us.
Once at speed the conditions are more severe by far than the Daytona banking. Full throttle for miles. Therefore have a look at the big aluminum timing cover on the right side of the Scout’s engine. See that stainless braided oil line? It sends oil past a lip seal, straight into the end of the crank, fresh from the oil filter. Drillings in the crank carry it to the crankpin. End-feeding the oil (rather than conventionally tapping it from the adjacent main bearing, automotive style) means “centrifugal force” works for you, not against you. A reliable low-friction oil film is the result—even though it may be less than two microns thick in the loaded zone (.00008-in). Burt Munro, too, had switched his streamliner’s crankshaft to end feed.
Recip parts are Carrillo rods and CP forged two-ring pistons. The stock Scout has piston cooling oil jets and so does this Bonneville special. The bottom end is stock: stock bearings, stock case, gearbox, and clutch (oh yes—stronger springs). I had the opportunity to talk with several of the engineers Saturday evening. They told me that the work they’d done and the understandings they’d achieved would be valuable in several other programs Indian is running.
“Does this mean the Scout engine might not be a cruiser forever?”
“Could be,” was the enigmatic answer.
What connecting rods did Burt Munro run? Indian’s originals were designed for 11 hp. He sawed and filed a set of steel ones from a truck axle, lasting 20 years (his “machine shop” consisted of a Myford lathe, straight out of the pages of “Trustee from the Toolroom”).
Back to the present! The 2017 Scout is lowered about three inches, with the original rear suspension units replaced by struts. An off-the-rack Airtech fairing (is that a Charlie Toy?) was narrow at the front so the team made narrowed fork crowns and the bars were narrow, turned straight down. Rider Lee Munro said the bike was super-stable at El Mirage, where on July 19th this year it went 186.681 mph.
“You get too aggressive, it’ll fight back,” he said. “I think of a bike as like an animal. I suggest; I don’t force it. Here, the center of the course is like slush, like melted snow. And it’s very rough, lot of holes, lot of bouncing.”
What would happen Sunday? Could Lee reach higher speeds with the longer acceleration afforded by switching to the long course? You get in line with the others and move up as the runs are made. Ahead of the Indian a couple of places was a 220-mph diesel highway tractor, powered by an MTU V-16 taken from a mining truck, making thousands of horsepower. Engines starting, lopey idles. Where else could you see a ’32 Roadster with a downforce-producing venturi underbody and an internal-compression engine intake diffuser?
The Indian starts and warms up. Reliable operation, sharp sound, professional response. Munro gets aboard and goes—no muss, no fuss. A disappointing 186.415 mph. Later someone comes to the door of the motorhome and asks engineer James Whisler, “Are you…will they make another run this afternoon?”
Whisler, looking up from the many data traces on his laptop screen, points out the window.
“See that flag over there? As long as it’s pointed up-course there’s no point in another run.”
He explained that Saturday there had been a 1-2-mph tailwind and today it was a 10-mph headwind. Plus the air’s thinner today—density altitude yesterday was 4,800 ft, but now it’s a gasping-for-breath 6,000. Teams in turbo classes can dial up their boost to detonation’s doorstep and have power, but the Indian’s atmospheric induction makes its power proportional to air density. There’s no point in fighting physics. Physics wins. Indian today has something Burt Munro did not: reams of data, gathered by the sensors that cover the machine, reported to the laptop through a USB cable plugged into the bike behind the rider’s left thigh. This is grand because it reveals things you’d never think of, but interpreting the data is a minefield.
“Every sensor you use is just a lie, an approximation of the real world,” Whisler said. Every sensor has a response time and a sampling rate. Think about it. If sampling rate comes close to engine firing frequency, strange “trends” can appear that are just artifacts of the system. False information. This is not push-button “computer racing,” but requires hours of staring at the data (just as the old-timers stared at spark plugs), trying to extract the real meaning.
What next? The engineers gathered valuable data and I suspect the hankering for 201 mph goes all the way to the president’s office. As Burt Munro used to say, “you just need one good run…”