How can you say Corolla is much better than city? Just because you say, it doesnt make it better.. give logical support to your claim my friend.. Coming to Dohc vs Sohc:
SOHC stands for Single Overhead Camshaft. This means that there is only one camshaft per header. Inline engines will contain one camshaft. V-type and/or flat will contain 2 camshafts. For a SOHC engine there are usually 2 valves per cylinder but there can be more with the addition of cams for each valve.
DOHC stands for Double Overhead Camshaft. Now there are 2 camshafts per header. So in an inline there are 2 camshafts because there is only one header, but there is 4 in a V-type or flat engine. These DOHC engines usually have 4 valves. One camshaft for the exhaust valves and the other for the intake valves. DOHC engines cost more for repairs. To ensure against expensive engine repairs, make sure you change your engine's timing belt about every 60,000 miles.
Cowratgee: If you read the above, you can clearly understand that SOHC engines lasts longer than DOHC engines.. SOHC engines are more fuel efficient.. Trust me, if honda is producing an engine, then there must be a solid reason for it... read carefully before posting any comment please.. Your nick really resembles COWrolla..