Inside Indian’s King of the Baggers V-twin

[Hugh Janus]

Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

Indian’s “Challenger” went 180 mph at Daytona this year. That’s 10–12 mph faster than a year ago. Things are heating up fast in this class, which has become American factory racing. At MotoAmerica’s Laguna Seca national on the weekend of July 10, the top Bagger lapped quicker than Eddie Lawson did on Yamaha’s fearsome two-stroke YZR500 in the 1988 US Grand Prix.

This stuns and surprises us, making this MotoAmerica’s most popular class. It’s the last thing we expect from heavy, long-wheelbase motorcycles designed for comfy interstate touring or chugging to Sunday club breakfasts. But we love to be surprised.

Indian Motorcycle’s race Challenger may be long and heavy, but anyone who has witnessed MotoAmerica’s King of the Baggers racing knows they are anything but slow and boring. (Brian J. Nelson/Indian Motorcycle/)

Indian’s riders in both KOTB and Super Hooligan classes are current class champion Tyler O’Hara and “the man who’s ridden everything,” development specialist Jeremy McWilliams.

Early this spring I attended Harley-Davidson’s pre-Daytona baggers race team test at Podium Club raceway, southeast of Phoenix, Arizona, to see the new racing class. Then I was invited by its great rival, Indian, to MotoAmerica’s Laguna Seca national near Monterey, California.

There, in Baggers Race 1 on Saturday, I saw O’Hara and H-D’s Kyle Wyman carve each other up in close quarters, flicking (Yes! Flicking!) down Laguna’s famous Corkscrew, then both losing the front entering turn 11, giving the win to Hayden Gillim on a Vance & Hines H-D. O’Hara somehow righted his 620-pound machine and restarted quickly enough to finish fourth!

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The two building blocks of that 180 mph Daytona speed are mighty acceleration off the chicane and the power to force the mandatory 29-inch-wide front fairing through the resisting air (sportbike fairings are 19–21 inches wide). Acceleration? Because these bikes have huge V-twin engines (Indian’s liquid-cooled Challenger 60-degree V-twin is 108ci/1,825cc) and long wheelbases over 65 inches, they are like 2022 MotoGP bikes with their variable ride height systems on minimum. Being long and low turns both into dragsters. I was told that on certain tracks the Baggers achieve quicker sector accelerations than Superbikes.

Why the 60-degree vee angle, when traditional Indians had 42 degrees? As such large-bore pistons approach bottom center (BDC) the vee angle must be large enough to prevent skirt-to-skirt clashing.

I had a long conversation with S&S Chief Engineer Jeff Bailey, who is supervising engine development (and as I would soon see, pitching in as a line mechanic when needed). When I repeated what’s often said about the class, that horsepower is somewhere between 155 and 165, he said, “More.”

More To Come

If we imagine that “more” is 170, we can combine that with the 7,700 rpm rev limit MotoAmerica gives Indian to find that this modified engine breathes and burns well enough to achieve a 162 psi stroke-averaged net combustion pressure (aka “BMEP,” for brake mean effective pressure). That number, about 80 percent of what is achieved in MotoGP or World Supers, indicates that this engine is at a decent but moderate level of development, implying more to come.

Running this engine to 7,700 rpm with its nearly 4-inch stroke (96.5mm) results in an average piston speed of 4,880 feet per minute and a peak piston acceleration of 4,020 G. Compare the latter figure with the 7,000 G regularly achieved in redlined 600 Supersport engines, or with the 11,000 G in MotoGP engines at 18,000 rpm.

Harley-Davidson’s larger 131-inch engine is given a rev limit of 7,000. Before upper rpm limits were set, engines were wrecked by over-revving but reliability now seems solid. Although stock Challenger bore is 108mm, for this class it is 110mm, giving a 112ci displacement.

“More” than 165 hp is being produced by Indian’s 112ci V-twin used in the KOTB Challenger. (Brian J. Nelson/Indian Motorcycle/)

Sitting to one side in Indian’s work area was a 9-foot-long wheeled engine cabinet containing two fresh-off-the-dyno engines, fully dressed and ready for use. At one end of the cabinet was a set of handlebars with a hand brake.

Compare Indian’s engine with Chevy’s famed 427 V-8, whose dimensions were a near-identical 108 x 95.5mm. If the KOTB-modified Indian makes 170 hp, four of them combined into a V-8 would make a perky 680 hp.

Intake System

On stock Challenger engines there are two vertical intake pipes whose oval cross section is equivalent to two 52mm round holes. Intake area was limited by the section of the cast main frame beam directly above the cylinder heads but the modified engine needed more air. The team elected to bypass the frame beam by making a CNC-ported and additive-manufactured right angle bend served by a giant 78mm throttle body on the right side. Despite losses likely associated with the bend, this gained 10 or more horsepower.

A massive air filter feeds a 78mm throttle body. (Brian J. Nelson/Indian Motorcycle/)

Development is always “triaged”: Early in the process, it’s the big items offering large gains that get tackled first. As the project matures, the focus can shift to smaller problems. This is an exciting time, as the technology is visibly changing from race to race.

Cam lift and timings are not regulated in this class, so when these engines are started they sound like V-8s with long cams. They ka-thump ka-thump until warmup evaporates more of the injected fuel, bringing in the second “voice.”

Lubrication

Because this is a modern all-plain-bearing engine, its life depends upon reliable delivery of air-free solid oil 100 percent of the time (bad things happen when air gets into plain bearings). But being originally designed for the low mounting position of a touring engine, it was not designed with a deep sump as found on Superbikes. Bailey told me there is a cavity behind the crankshaft into which the scavenge oil is pumped, assuring that the pressure pump’s intake will remain submerged.

Internal Parts

As in sportbike engines, Challenger’s crankshaft is a one-piece forging having a single crankpin carrying the two connecting rods side by side rather than in a single plane in fork-and-blade fashion. For this reason its separate Nikasil-plated cylinders are offset by the thickness of one rod.

Primary drive from crank to gearbox is by gear, and drive to the rear wheel is by an S&S chain conversion.

Power to the rear wheel is delivered by an S&S chain conversion. (Brian J. Nelson/Indian Motorcycle/)

In early development it was found that the crankshaft flung off too little oil to guarantee gearbox lubrication, so oil jets are provided (there are also piston-cooling oil jets). Like the two-speed Indians that finished 1-2-3 at the 1911 Isle of Man TT, this six-speed gearbox is shifted by light dog-rings rather than by sliding the substantial gears themselves (one key to quick shifting is to reduce the total mass that the rider must move when changing gear).

Chains drive single overhead cams in each head, originally operating four valves per cylinder by forked rockers carrying compact hydraulic clearance adjusters. S&S provide billet rockers with mechanical lash adjustment, eliminating the mass (and a possible “pump-up” rpm limit) of the hydraulics.

Shaping the Torque Curve

When this engine was originally conceived its torque curve was planned to be “rainbow-shaped”—emphasizing midrange acceleration essential for on-ramps and passing. This is in contrast to what was long traditional for such bikes—the “lean-to” torque curve of older two-valve big-inchers—with peak torque at the bottom, decreasing as engine speed climbs, and finally wheezing out approaching 5,000 rpm.

As with any modern engine, Challenger’s torque curve shaping is achieved by a combination of port and valve sizes (in what rpm range will the intake velocity best for cylinder filling occur?) plus intake port downdraft angle (how will the kinetic energy of the intake flow be divided between the two tasks of cylinder filling and the generation of combustion-accelerating tumble motion?).

Compression and Head Temperature

Cylinder heads on Indian’s KOTB engines are CNC-ported. Stock compression ratio of 11-to-1 reflects the value of liquid-cooling, but because the competing 131-inch pushrod Harley circulates cooled oil between its paired exhaust valves, it probably doesn’t suffer as much from high head temperature as a pure air-cooled. Compression ratio may therefore not be that different between the competitors. Maximum torque is achieved by running the highest compression ratio possible without knock on the fuel provided.

Tyler O’Hara flicking the Challenger through the bottom of Laguna Seca’s famed Corkscrew. (Brian J. Nelson/Indian Motorcycle/)

The fuel in this case is VP’s T4, characterized as a pour-in replacement for pump gasoline. It is lead-and-ethanol-free but does contain the oxygenate MTBE.

Exhaust System

The exhaust headers begin with additive-manufactured stainless pieces joining the head ports to cut-and-welded head pipes that merge into a large high-mounted and horizontal collector. Each cylinder has its own oxygen sensor, allowing it to be tuned as a “separate engine,” with its own fuel and spark maps. The large exhaust collector brought important gains. Because the engine is wide and originally mounted quite low, it’s difficult to arrange for equal-length header tubes and still stow the collector under the right-hand footpeg. Again, because this engine was born to tour, it was designed “backward”—with the compromise falling on the exhaust system (in the form of sharply curved exhaust ports) rather than on the chassis.

On Friday I learned that the engines had a few new parts on them not tried before, but they were only an ignition rotor cover and primary cover, both in low profile for cornering clearance.

Old and new tech—and cut-and-weld and additive manufacturing—is used to create the Challenger’s massive exhaust system. (Brian J. Nelson/Indian Motorcycle/)

Tyler O’Hara’s crew chief Al Ludington (who was at American Honda Racing in the Miguel Duhamel years) said the riders typically use five of the six transmission speeds: if you ignore first, the ratio of second to sixth resembles a proper roadrace trans. But from first to second there is a whopping 47 percent drop in engine rpm!

The weekend showed that Indian certainly has competitive power but that Harley may at the moment have more sophisticated control over theirs. Ludington summed up by saying, “On a clear track we can do the lap times, but in a race there can be another bike blocking you.” He noted that corner exit and acceleration are already good. The present problems are in braking and corner entry. He also said, “The bike responds differently to the rider in right- and left-handed corners.”

When a bike is capably ridden near its grip limits, small improvements in engine throttle connection and smoothness can have large effects. Riders on the 2023 MotoGP Ducati speak of such improvements over the previous year’s software. In racing, time, funding, and resources are always in crisis. Everything is a race—winter development, spring testing, and every practice in season.

Pay attention to this racing class because it has the full attention of major American corporations. It is a fast-advancing demo of all the techniques of racing development and rider versatility being applied to a class of motorcycle no one ever imagined on a racetrack.

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