An air-cooled twin vs a liquid-cooled six?
Yep, Your expert buddy needs to go back to school Matt.Air cooled Harleys are not what is currently available.
I think the TOTL Ultra H-D engine has been liquid cooled for close to 10 years now.
My H-D V-Rod has been liquid since it's intro in 2002, that's 20 years for the math deprived.
But the air-cooled H-Ds are still around too, many riders demand them.
Lighter, less complexity, less to go wrong.
BMW, Ducati, Moto Guzzi, more still do air-cooled.
Personally I've never been a bagger type guy.
I go back to the 60s when the first thing we did was strip off all that overweight garbage and throw it in the trash.
Bagger guys equate the size of their bikes to their pecker, wrong. LOL