Originally Posted by Jonny5

You need to figure the area of the hole for an accurate measurement, not as simple as just adding the sizes together. For example:

2 hole 1.6 = 4.019mm˛
3 hole 1.3 = 3.979mm˛

Between these two, the same static (bench) damping is easily achieved, most likely with the same oils as the difference between them is negligible at best. But the 3 hole pistons will have more pack in an equal comparison compared to the 2 hole pistons. This is because there is an additional hole with additional edges to shear against the oil as it passes through.

The machined 4 hole AE pistons have a tighter tolerance, leading to less oil "blowing by" the sides of the pistons, hence more holes AND larger holes.