Water cooling produces a more stable operating temperature range and thus tighter tolerances can be held. Air cooling isn't really worse than water cooling from a power standpoint, but tighter tolerances allow you to get more power because you can shed heat more easily (as the others said). It's hard to add heat-shedding power to an air-cooled engine without making it bigger. If it's water-cooled, you can just make the radiator larger.

 

Water cooling allows more constant and regulated temperatures which, as already metioned, allows tighter tolerances. tighter tolerances make a tighter engine which will produce more power.

Don't worry about how water cooling will affect the sound. If you water cool a Harley v-twin it will sound the same, maybe lose some mechanical engine noise (good) but not the harley sound.

Honda and suzuki both have liquid cooled transverse v-twins like Ducati... sound almost the same. The distinctive Harley sound is more more a function of the firing order and off-set crank pin than how it is cooled.

 

Cooling does a lot towards increasing horse power, but the real reason liquid cooled engines develope more power is because they allow higher combustion chamber pressures.

That's my story and I'm sticking to it.

 

That's the answer. The tolerances in Harley engines are sloppy by comparison (because they have to allow for expansion at lower RPMs). Because liquid-cooled engines can keep their temperatures and expansion under better control, you can design them to run at considerably higher RPMs (eventually, the heat generated will overcome the cooling system's capacity, so there is a limit with those engines, too).

So, tighter tolerances that allow for higher RPMs, which require more exact valves, cams, etc....it all adds to a lot more HP. Eventually, the increase in HP makes the lack of proportional increase in TQ irrelevant.

That's why sportbikes with comparatively weak torque curves can redline at 13,000 RPMs and still put any Harley to shame.

Interesting engines are the Ducati air-cooled L-twins. They use modern technology in valves, cams, etc., and can, therefore, still wring out more HP and TQ than an air-cooled Harley V-Twin of comparable displacement.

But that's not why we buy Harleys, is it?

 

what do you mean "should"? you do know that harley has already introduced a water cooled bike, right?

 

I think you meant to that the sound was a function of the firing interval and a single crank pin (not offset)

 

Because the amount of energy generated by the combustion is higher, since u r starting from much lower temperature (comparing to a hot engine) towards a high temperature (combustion moment).


Hot engine

Combustion temp <<<<<<<<<<<<<< prior combustion temp (hot)
x---------------------------------------------------x


Cold engine

Combustion temp <<<<<<<<<<<<<<< prior combustion temp (slightly colder)
x----------------------------------------------------------------x




The length of the line represents the amount of combustion energy which gets converted to dynamic energy through the piston, crank, gears then the belt, so the bigger the better.

 

Let me ask a related question. Why is water cooled better for EPA emissions purposes? Is it because the higher temps produce more complete combustion? or what?

 

allows for tighter tolerances more rpm and reduces heat

 

Heat is power,power produces heat.