Originally Posted By: DriveHard
I can't find any official statement from Harley stating why they have the rear cylinder de-activation other than for rider comfort, but I do suspect that they would not purposefully publish that it is needed to not cook an engine. I do know that I found an article published by Popular Mechanics that specifically states the purpose of the rear cylinder de-activation is to keep from cooking the engine.
http://www.popularmechanics.com/cars/motorcycles/a11811/harley-davidson-rear-cylinder-cutout/
Harley-Davidson's air-cooled V-Twin remains a stubbornly anachronistic signature of the American motorcycle manufacturer, and its most potent expression comes in the form of the 110 cubic inch (1,803cc) Screamin' Eagle lump currently found in the CVO lineup. Producing 122 lb-ft of torque, this is the most powerful Harley engine to date; as such, an oil cooler can only go so in protecting this puppy from soaring temps.
How does Harley keep this mill from melting when mercury hits triple digits? One feature engineered into air-cooled Harley engines is a function called Rear Cylinder Cutout. Because the aft cylinder tends to run warmer since it doesn't benefit from the airflow that hits the front cylinder, RCC seeks to equalize the difference by shutting off fuel and spark to the back cylinder if the engine idles for more than 3 seconds above 288° F. Once the air-only mix drops the combustion chamber temperature to 275° F, normal operation resumes. RCC was introduced in 2008, and was actuated by a cable before the 2009 model year, when throttle-by-wire technology was introduced.
While automotive applications frequently implement cylinder deactivation for MPG improvements, we won't hold our breath for that functionality to be applied to bikes; after all, motorcyclists are usually more interested in staying cool than saving fuel.
EITMS is purely for rider comfort. When it
activates and “shuts off” the rear cylinder, it’s
not because the motor is overheating. It’s
designed to reduce the heat radiating from
the rear cylinder to the rider.