Indian's Big Reveal: The New Thunder Stroke 111 Engine

Indian Motorcycle Unveils Mill That Will Power New 2014 models

The wait is over: After months of sound bites, fuzzy images and subtle design hints, Indian Motorcycle finally pulled the wraps off its all-new Thunder Stroke 111, the new engine that will be the literal heart of the 2014 lineup of new Indian Motorcycles to be introduced later this year.

The spec sheet description doesn't sound all that unusual at first blush; the 'Stroke is an air/oil-cooled, 49-degree V-Twin with a 101mm bore and a 113mm stroke, for a total displacement of 111 inches. The rigid unit construction sports a gear primary drive to the six-speed overdrive transmission, and a forged single pin crankshaft is designed to withstand high levels of torque. Up above, three cams actuate four pushrods that operate two valves per cylinder with hydraulic valve lifters, allowing for a reduction in overall height and centralizing mass. Electronic sequential port fuel injection doles out the juice, and electronic throttle control dictates the power, with a multi-plate wet clutch to manipulate the transmission.

But this unique lump actually looks attractive, too -- the entirely new, clean sheet design draws on a 1940s-era Indian Chief twin as its inspiration and visual template, and shares nothing with the power plants of the failed Indian models that preceded it. It manages to bridge the gap between evocative and modern, at least judging by the photos and the mechanical components we've seen. Styling highlights include tapered cylinders (sporting larger diameter heads, like the Indians of yore), rows of outwardly-angled fins, and those large-diameter parallel pushrod tubes. Period-appropriate ribbed valve covers topping off the power plant are also a very cool and distinctive detail.

Polaris aimed for a relatively healthy 9.5:1 compression ratio on the Thunder Stroke, and seemed determined to keep the internal parts light and up to date. The short-skirt pistons are driven by narrow and light con rods. A single counter-balancer controls vibration. Surprisingly, maximum engine speed is a claimed 5500 rpm -- which seems fairly low , given the effort to minimize weight and friction.

The six-speed gearbox goes with straight-cut gears for first gear, and utilizes quieter helical-cut gears on second through sixth, for smoothness and reliability. The large clutch (with aluminum basket) is designed to minimize lever effort, and the final drive is a carbon-reinforced belt. Indian makes no power claims just yet for the new engine, but they do claim that torque is "more than 115 ft. lbs."

Thunder Stroke In Action

To demonstrate the Thunder Stroke, Indian also rolled out the Spirit of Munro, a brand new custom streamliner named after legendary Burt Munro, who set the land speed record for a motorcycle under 1000cc riding his Indian Scout in 1967. The Spirit was designed by Jeb Scolman, of Long Beach fabricator Jeb's Metal and Speed.

The Thunder Stroke 111 will be built at Polaris's Osceola, Wisconsin facility, and then trucked over to the production plant in Spirit Lake, Iowa, for final installation into the new series of 2014 models. Hopefully we'll see them in action this summer.

Check out this video animation for an excellent close-up look at the Thunder Stroke 111:

Thunder Stroke 111 Engine Specifications

Type: Air/oil-cooled 49-degree V-twin (Featuring integrated oil cooler; semi-dry sump oil system and oversized oil radiator).

Displacement, bore x stroke:111 cubic inches (1811c); 101 x 113mm

Valve train: OHV; 3 camshafts, 2 valves per cylinder, pushrod actuated via hydraulic valve lifters

Fuel system: Electronic sequential port fuel injection; electronic throttle control

Throttle diameter:54mm

Compression ratio: 9.5:1

Transmission: 6-speed overdrive, constant mesh, helical gearbox

Clutch: multiplate wet clutch w/aluminum basket, integral torsional damper

Final drive: Carbon fiber reinforced belt