A push rod engine has the camshaft in basically the centre of the engine. As it turns it pushes lifters and pushrods up and down. The pushrod pushes the roller rocker up, which causes the roller rocker to push down on the valves (and open them). The Roller rockers are just that, rockers, "hinged" in the middle.
As you can imagine all these parts moving creates a little more friction (HP loss) and takes a little more time to open and close the valves (I'm talking factions of a second).
A SOHC or DOHC motor has the cam shaft in the head. As the cam shaft turns it pushes more directly on the valves. It is more efficient method of opening and closing the valves.
Most (I think all) import motors or SOHC or DOHC (single over head cam or dual over head cam ) engines.
Most ignorant ricers (and even ricer Magazines!) think that just because a mustang has a V8 that it is "old" technology. What they fail to realize is that the V8's have close to the same technology, we just have larger displacements.
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