hello!
SOHC= Single Over-Head Cam...
DOHC=Dual Over-Head Cam....
SOHC engines has got one Camshaft running whereas DOHC has got dual camshafts...
Valves Distribution on DOHC is quiet easier as compared to SOHC engine...more than 12V engine on SOHC is more complex...whereas DOHC has got one camshaft for inlet valves whereas one for exhaust so its quiet easier to understand and not so much complexions...DOHC give high end performace as compared to SOHC...so all way DOHC engines are much better than SOHC ones but take more space and heavier than SOHC ones....
Thanxxx