Typically the advantage of the overhead cam is that you can have four valves instead of two. Theory being that you can get more area with two valves than one.
They tried to go with a dual overhead cam when developing the 5.7 Hemi, but found that with the "Hemi" head design, that they could put two valves in per cylinder and with the bigger valves get more surface area with one bigger valve, than two smaller ones.
Area = Pi x radius**2 = Pi/4 x Diameter**2 = .7854 x Diameter**2
For 1" diameter:
Area = .7854 x (1)**2 = .7854 x 1 = .7854
So two 1" diameter valves will have:
2 x .7854 = 1.5708
For a 2" diameter:
Area = .7854 x (2)**2 = .7854 x 4 = 3.1416
So, it is better to run a 2" diameter valve, than two 1" diameter valves.
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Yes, you minimize the rocker gear weight by eliminating the push rods, but you now need a longer timing chain/belt which will have more stretch/variation. This will stretch more than the timing chain needed for an internal cam push rod engine.
Not to mention Timing both cams in to by in synch with each other. They had some problems with the 3.5 dual overhead cam engine for getting both bank cams in phase.
Dual overhead cams is not the end all and cure all for valve train, like the propaganda has tried to influence you into thinking.
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The 2.0 L had a dual overhead cam and single overhead cam version. The single overhead cam engine was made in Trenton, MI, and the dual overhead cam engine was made in Mexico. Both engines had 4 valves per cylinder. The single overhead cam engine used a "forked"/split rocker arm that had one input for the exhaust cam lobe, then two outputs for each valve. That forked rocker arm was very expensive to manufacture, and making a dual overhead cam to eliminate the forked rocker arm was cheaper because two single exhaust rockers were cheaper than the one 'double' rocker arm in the single overhead cam.
