72 cm me timing chain 82 links ki ha like CD70, old sohrab, old pak hero etc
78 cm me timing chain 84 links ki hai like DYL Dhoom, new Sohrab, new Pak heo, star etc.
here is also difference of piston lenghth. 78cm wali bike ka piston 72 se lenght me 2 or 3 cm ziyeda hai
esi terha dono k cyleder lenght me b 2 cm ka ferk hai
usually 78 cm3 wali bike has more pick up, more speed and more power bt its life is short than 72 cm3's.