Modular vs. Pushrod engines

I've read a little bit on modular engines. But I still do not understand why or how they can only have 4 or 2 valves. How do they work? What is different about a modular engine? Are they all overhead cams like imports? My brother has a 4.6 Mustang GT with such and engine. When we work on it is there anything special that needs to be done?? (my engine knowledge is based off of traditional 90degree small block chevys)

They don't have only 2 or 4 valves... total. It is 2 or 4 valves per cylinder, and now even three.

They "work" by actuating the valves from one or two overhead cams per head. 2&3 valve/cyl engines use a single cam per head, while the 4V/cyl engines use two cams per head. The valves are actuated by roller followers that rest on the valve stem on one end, and a "lash adjuster" (spring loaded lifter) on the other end as a pivit point. The cam is basically centered over the middle of the follower where the roller is.

So the only thing that significantly differentiates a modular engine from a typical 4 banger import is in how the cam is manipulated, chain vs. lifter? (other than the obvious # of cylinders, and rev range)
3 valves is unsual. 2 for intake 1 for exhaust?

www.howstuffworks.com (http://www.howstuffworks.com)

Check it out. pretty cool.