Dual Over Head Cam, meaning there are 2 cams above head cylinder head, for a total of 4 cams in a v6, v8. A Single Over Head Cam has 1 cam over each cylinder head, meaning 2 cams total in a V6, V8. A pushrod engine (picture old V8) uses 1 cam centered between the 2 cylinder banks for a total of 1 cam in a V6, V8.
I think I disagree with that assessment and that site. Reason? What do they have to say about a Quad Cam V6? Here's how I see it:
Single Overhead Cam - 4-cyl one cam over the valves controlling both the intake and exhaust valves
Dual Overhead Cam - 4-cyl one cam for the intake valves and one cam for the exhaust valves; V6 one cam in each head controlling the intake and exhaust valves of each of their respective heads.
Quad Overhead Cam - V6 two cams in each head each cam independently controlling the intake and exhaust valves.
You are correct Grough. Although a quad cam motor can still also be considered a DOHC motor since on a V block there are two heads with both carrying two cams. Could be broken down to a dual cam pver each head, but that just sounds retarded. DOHC just means there are 2 cams per head, regardless of how many head/banks there are.
The SOHC/DOHC thing definitely applies to the number of cams per head. Thanks to the W12 and W16's from VW/Labroghini/Bugatti counting the number of cams in the engine is no longer quite as practical.
Manufacturers started including the cam count in their engine descriptions as an indication of how powerful the engine might be. But now there are so many other additional items that indicate the relative power of the engine: number of valves per cylinder, variable valve timing, direct injection, turbo/super charging, etc.
Its actually more precise to refer to the number of valves per cylinder rather than the number of cams per engine. You can have 2 or 3 valve engines with SOHC, 4 and 5 valve engines with DOHC.
In our case we have a 24 valve V6 with variable valve timing.