SOHC Vs DOHC

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When a member told me that most cars are sohc, it made me wonder why that is, in that, is one better than the other for driving, or just cheaper?

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ok, so i'm getting the picture that SOHC is cheaper to produce an maintain.
an if the mclaren-merc SLR is SOHC then getting good performance cant be a big problem i assume?

but i also assume that as it has fewer parts than a DOHC engine, wouldnt that make it more robust an durable from knocks etc, an simpler to repair?

in fact wouldnt they best be used for armoured cars an tanks which need a tough powerplant.

how about a new military vehicle then - with SOHC engine, mechanaical diffs, an electric aids other than headlamps...?