Dart,
You do NOT want zero hot lash, 2nd time now. For a number of reasons. Sol lfters have no give. Hyd lifters do. If you set sol lifters to zero, that is what you get. The point on the Base Circle where you set the lash might be a low point. [ Cams, like everything man made has tolerances ]. This is called BC run out. If the spot where you set the lash is the low point, then the the valve is held off the seat for the remainder of the BC. Another MOST important function about lash adjustment, not mentioned, is this: the heads of the valves [ particularly the exh ] get very hot while the valves are open because they are exposed to the combustion chamber heat. They dissipate this heat through contact with the seats in the head. Less time in contact, more chance of burning valves.
Setting lash at zero when 'hot' does not mean it stays at zero all the time. A few high rpm runs might get the exh valve hotter than when you bench set the lash at zero. The exh valves now expands more & holds the valve off it's seat. Lost power & possible damage. This is why there needs to be some lash to allow for these variations. Zero lash will also have a veeeeeery rough idle, may not idle at all because you have massively increased the seat timing & have little or no idle vacuum. Hyd cams have short clearance ramps because the hyd lifter provides a cushion. Because of the short ramp, having the lash too high risks getting onto the flank of the lobe where the acceleration rate is much higher. This is why 0.006-8" is a safe number & covers all eventualities.
