I had a 89 air cooled 350 Big Bear with small oil cooler and no fan assist and never had a over heating problem. I had a 2001 450 Foreman with a oil cooler with fan assist and sometimes I could not even see the motor because it was so caked in mud yet I never had to give it a cool down period.

Some people say once the cc get larger than you need liquid cooling but I ride with a guy with a 99 600 Grizzly air cooled and it never over heats and it has 5,000 miles on it.

When I traded my 450 Foreman for a Sportsman I was only after more speed and a comfy ride, but I was not excited about going to liquid cooling at all.

 

I've had a number of air cooled 4 strokes. I put well over 10K on a XR600 and had no break downs. It could be a bear to restart when riding slow speed stuff at temps over 90F. The head on that thing would get so hot it would ping too. The oil just wouldn't last as long eiter. It was pretty tired when I sold it, but it still ran. I have no doubt liquid cooled engines last longer, particularly in a warmer climate. The TBO is usually longer with l/c than a/c on aircraft. They can better tolerate a higher state of tune as they are more temperature stable, so they can built to more exact tolerances. How much longer the l/c will last is the question? They both have their advantages and disadvantges. Maybe we will, but I doubt we'll see an air cooled FI motor on ATVs.

Jeffin, I am assuming those are crank numbers. However, the Hondamatic is not as inefficient as you think. At 1 to 1 it is locked up (no fluid loss) and as efficient as the manual. Fluid loss is the only way to change ratios, it is designed with inefficiency for lower ratios. Manuals are less efficient in first gear than at 1 to 1 too.

Seat of the pants they are close enough for me too.

 

Yeah, back in the day I used to use a big red 3 wheeler to spray weeds at a farm I worked at for summer break from college. Involved idling while spraying, moving a few feet at 1 mph, repeat. That machine had done that for season after season, often in temps close to 100 and it never missed a beat.

One day the farmer asked me to change the oil in all the three wheelers with Rotilla T. I asked if he had filters, and he replied "they have filters?"

I think Honda is pretty conservative when it comes to using more finning than they need to for the power level of the particular motor. I've seen them live through hellish abuse for thousands of hours.

Actually, more recently I once got stuck in stop and go traffic on a day that was 116 degrees out, on freshly rolled asphalt, on a Buell.

Considering the thing was tuned to around twice the HP of what the engine platform was originally intended to produce, I thought it would melt down, but it did fine. I, on the other hand, started feeling queezy and seeing spots, and had to stop at the next market for some cold water...

I also had one of the air cooled DR650s that I think had about 12k of hard miles when I finally sold it. It ran perfect, and still sounded quiet and tight.

Bottom line for me, anyway, I think either air or liquid cooled engines can both perform fine, as long as it was engineered well.