| air cooled relys on the ari it breaths in to coole it down, more air let in the beter the engien works
water cooled replys on the water cooling system, the water is alsys cold so then engien is geting the maximum amount of coling so it woks much beter
the polin type (name brands/italian bikes) are generaly several times faster then the CAG bikes from china (CAG is what the bikes from china are commonly referd to as) the reason being is that the italian bikes are made of the finest materials (like in cars) howerver it comes at a price up to 10grand for these bike (NO JOKE) you could by a decent full size for that price
hope this helped you | 
