8) most dual valve springs are misnamed. they usually have a dampner spring to reduce harmonics, and is usually the way to go if you have the choice. as for what lobe center to use, first decide what rpm range the engine will spend about 85% of its time in, the select a cam that works in that rpm range. for instance if the engine is going to see street use primarily then select a cam that works is the 1000-5000 rpm range. oyu can fudge that up or down a few hundred rpm if you want a bit more or a bit less cam.