[Greg Reimer 7376]

Some variables exist between motors,even of the same brand and even configuration. Valve lash can be affected by numerous things. Probably the best way to weed out some variables would be to carefully set valve lash cold,knowing exactly where you set it, running the engine to operating temp, then checking it hot. Now, operating temp at the end of a hard pass would be hotter than a 10 minute warm up.That would affect exhaust valve lash more than intake because of the greater heat of the exhaust gas passing the valve.The important thing is to know exactly how much the lash tightens up between temperature extremes. The main thing is to still have .002-.003"lash at the heat extreme.
You definitely need to find the fine line between loose valves and lost lift,and tight valves, lost power and compression loss due to valves not seating at the finish line. If adding that much lash caused that much loss of lift, maybe you should try a set of pushrods that are .030"-.050" longer. That would work with the engine's valve train geometry to bring the lift into an optimal setting. Also, too much lash with Schubeck lifters kind of scares me with some of the stories about the ceramic base of the lifters failing. You need to compare cold lash with hot lash on that particular engine you're racing and working on in order to determine exactly what works. A good motor is like a good woman. It will talk to you and you can figure out exactly what it wants. They can both get quite loud at times,however.