Ep 49 – Air Cooled vs Liquid Cooled Motors and Harley’s New Patent

On today's episode, we go over the primary differences between liquid cooling and air cooling a motorcycle motor while also discussing some changes we may be seeing from Harley.


First Up, Let’s discuss the best way to cool an engine:

As we know, Harley loves their air-cooled v-twins; however, in MY 2002, they broke the mold with the Revolution engine. For the V-Rod, the motor company teamed up with Porsche to build a “revolutionary” new motor for a race worthy cruiser. The engine was significantly smaller than the Dyna, Softail, and Touring motors, yet produced insanely more power. So, is there a direct correlation between power and cooling?

Liquid cooled engines:

  • Higher Revving - Providing for higher HP numbers
  • Run higher tolerances due to better heat management, which allows for the higher RPMs
  • Run more efficiently, less pollution, less heat on the back cylinder, less likely to cause detonation
  • Run quieter, as the water jackets insulate the sound quite a bit
  • Finally, because of the heat management provided by liquid cooling, the bike can maintain more consistent temperatures when running harder or when stuck in stop and go traffic, allowing for the rider to be more comfortable

Air cooled engines:

  • Run richer, causing greater pollution and higher NOx release
  • Run louder
  • Air cooled engines provide more simplicity, with one less component which could
  • break, need to be replaced, or need servicing
  • Air cooled require less maintenance (liquid coolant requires coolant change every 6,000 miles or so)
  • Cheaper to build an air cooled bike - Wait, what?

For Harley, they currently have liquid cooling on some of the Touring models, and on the Revolution X powered Street models, and for MY 2020, the Pan America and Streetfighters will be powered by their newest motor, which will be liquid cooled…


So which is better?


Speaking of something better:
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With the Pan America and Streetfighter, the Custom, the Streets, and the Twin Cooled Touring Models, are we seeing the shift at Harley to water cooling? 

In August, Harley’s latest patent hit the Patent Office website, and it is showing some promise:
A new big v-twin is coming in the near future, and with a new overhead valve design with higher revs, we may be looking at the first big twin that is built to be liquid cooled?

So what is actually going on here:
Current Harley pushrod configurations in the Milwaukee 8 motor moves a pair of rocker arm shafts that control the two intake and two exhaust valves. This new engine will get rid of the rocker shafts and move to a single rocker arm design, which will take the current setup of the 4x pushrods on the right side of the motor, and relocate 1 pushrod per cylinder to the left side.

Why is this important? Since the F-Head motor, so from 1914, all Harley engines have had their pushrods located on the same side of the motor, the right side. This is a new “radical” design for Harley, and will allow for a big change in the motor’s performance capability. Today, the Milwaukee 8 redlines around 5500 RPM; however, the new motor is claimed to have a redline around 6800-7000 RPM. Does this actually matter? Of course it does, higher revs allow engines to reach higher horsepower levels.
With all this information, about liquid cooled vs. air cooled motors, higher RPMs coming out of new configured heads, where does this actually take Harley? As we saw in the Revolution engine co-designed by Porsche, it was a lower displacement, higher revving, liquid cooled motor, that produced more overall power than any other Harley motor before it. With that said, lets take a look at the motor going into the Pan-America and Streetfighter. Lower displacement, liquid cooled, we won’t know the torque and power until they are released; but I am betting we will see a higher revving, higher horsepower motor, that will knock the socks off the big twin Milwaukee 8 in the softail and touring families. This also tells me that Harley will have to do something for both families to ensure their flagships remain desirable to the mass markets. I feel this is just another step in the future of Harley that will keep it viable in the heavyweight motorcycle market, yet still be viewed as a great bike for the younger generations of riders who are quickly becoming, if not already, the largest purchasing segment in the world.

Thoughts on this:

Closing Argument:
Would having a radiator on your bike really upset you from a design perspective?