12 Reasons to Love Your Air-Cooled Engine

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12 Reasons to Love Your Air-Cooled Engine…

Twist the throttle and you instantly know you’re on a Harley. The signature sound. The immediate low-end torque. The tingle up your spine. It’s all due, more than anything else, to the air-cooled, V-Twin engine that has defined Harley-Davidson for the past 100 years.

Yet while the essential air-cooled V-Twin architecture has remained in place, the technology within moves forward rapidly. In an age when increasingly strict, worldwide regulatory emissions requirement shape the motorcycle world, the venerable air-cooled V-twin remains at the heart of many Harley-Davidson models.

There are good reason to love your air-cooled Harley-Davidson engine. Lots of good reasons. Here are just a dozen…

1. They’re Smart!

Since 2007, all Harley-Davidson engines have utilized Electronic Sequential port Fuel Injection instead of carburetors. The ESPFI system controls fuel/air delivery based on air density, throttle position, engine temperature, and exhaust oxygen sensors. The engine control module monitors these sensors, adjusting the fuel delivery for optimal engine operation.

In addition to controlling the fuel/air mixture, H-D engine management systems control ignition timing based on engine temperature, air temperature, load on the engine, and RPM.

2. They’re Clean.

During the past decade or so, meeting ever-more-strict exhaust emissions requirements around the world has become a primary influence on engine development and calibration.

The Motor Company must achieve emissions compliance in the more than 50 countries in which it sells motorcycles, which often requires unique calibrations or equipment for various markets.

3. They’re Efficient…

The long-stroke/small-bore, two-cylinder, low-rpm design of Harley-Davidson air-cooled engines has inherently low frictional power losses.

4. …and Powerful.

The Harley-Davidson design also produces its signature strong torque at low and midrange engine speeds, where most people ride most of the time.

5. They beat the Heat.

Achieving emissions compliance has required leaner fuel/air mixtures, which in turn could produce a hotter-running engine during long periods of idle. For those interested, Harley-Davidson made the Engine Idle Temperature Management System (EITMS) available, beginning with certain 2007 models. At idle, when the engine reaches a certain temperature, EITMS shuts off fuel to the rear cylinder, leaving it to idle only on the front cylinder, thus cooling off the rear. To improve heat dissipation, cylinder-cooling fins on the Twin Cam engines are wider than on the Evolution engine.

6. They’re Balanced.

The counter-balancers on the Twin Cam B engines used in the Softail family cancel 100 percent of the primary imbalances of the engine, eliminating the need for rubber mounting. Significant engineering produced a balanced engine, of which outside appearance is nearly identical to the non-balanced Twin Cam by having the balancer drive within the cases.

7. They Sing.

The signature sound Harley-Davidson air-cooled V-twin engines is primarily the result of a narrow 45-degree bank angle, bore-to-stroke ratio, and precise intake and exhaust tuning. Over time, regulatory noise requirements have presented a significant challenge to preserving the iconic sound. Intake, exhaust, and mechanical noise together represent the majority of the bike’s sound footprint. To promote higher levels of legal exhaust sound, other sources are engineered to be quieter. Cylinder fins are cut and shaped, gear teeth are ground and honed, cover and cases are shaped and formed. All are analytically modeled and tuned to minimize mechanical noise output.

Other refinements, like a hydraulically tensioned roller chain cam drive system and mechanically tensioned primary drive system, have been designed to create a superior engine sound quality. The end results are an orchestra of sounds that continues to be legendary and rumble along.

8. They Stand the Test of Time.

In the mid-1970’s, the consensus of many within the motorcycle industry was that air-cooled engines would soon be “dead” because of their inability to meet emissions regulations. Today’s engines defy that notion. Thanks to the combination of precise electronically controlled spark timing and fuel delivery with 0(2) feedback, efficient intake systems and camshafts, and 3-way exhaust catalysts, Harley-Davidson engines meet or exceed current emissions requirements.

9. They’re “Streamlined”.

In addition to their aesthetic appeal, air-cooled engines are inherently simple without the radiator, water pump, and plumbing required of liquid-cooled engines.

10. They’re Durable.

All Harley-Davidson engines designs are subjected to rigorous durability testing that includes dynamometer testing for hundreds of hours and thousands of miles.

11. They’re Historic.

The 45-degree, inline V-twin has been a hallmark of Harley-Davidson engine design since 1909 and the introduction of Model 5-D.

12. They’re Beautiful.

What other motorcycle company makes the engine the centerpiece of its design?