[Jeff Alton]

Great questions!

I am not sure what testing goes into making the recommendations. When one says 1.25 is suggested did they test 1.0 and have an issue? What was the safety margin, or do they just know that no one has had and issue with 1.25?

I am pretty sure it comes down to data points. As in known cases where X clearance worked or did not work at certain RPM (based on specific cam and spring data). Measuring the flex and stretch in the crank, bearings, rod, pin, piston, valve and spring, heat expansion etc would make empirical guessing difficult.

Should make a good discussion, especially if we can get it backed up with true empirical data!