the reason I was given for not using synthetic for break-in was it didn't provide enough "traction" to spin the lifters properly for break-in. This was from crane cams technical support. They recommended using mineral oil for the first 20,000 miles. An inverted bucket lifter is indeed similar in some respects to these type lifters. However it is a 1-1 ratio, which reduces the loading on the cam, a 1.7-1 ratio would make a 100 pound spring produce 170 pounds at the cam, there is no pushrods or rocker arms to present a substantial amount of inertia to overcome, requiring heavier springs to get the same results, reducing the load on the cam even more. Most of these designs are 4 valve heads, requiring valves about half the weight allowing an even lighter spring, and the tops of the buckets are quite a lot larger in diameter than most of the lifters we are used to, allowing a larger base circle. So basically they aren't really comparable at all.
