Originally posted by M54 Powered
let me rephrase:

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2. most 4 valve per cylinder engines are DOHC because it's easier to design them that way. SOHC engines tend to be 2 valves per cylinder. of course, there are exceptions to both.
Tama po ito. DOHC is said to be more practical esp in 4v/cyl. Because if you had just one camshaft, there will be so many cam lobes on a single shaft that'll make it heavy or just too bulky. Here's a good link: http://auto.howstuffworks.com/camshaft4.htm