I`m not sure what manufacture of lifters those are, but if they are Hylift Johnson, this is from their catalog about the "R" suffix.
“R” or Race Design: These parts have an “R” designation after their part number. So a Race
Design part number will look like A-0817R. These Lifters have a Leak Down on the lower end
of the scale from 8 to 20 seconds. In the performance application these lifter will actually
“Bleed” down and result in an effective loss of valve lift and duration at lower RPMs. These
are also referred to as “Variable Duration” Lifters and will supply a better idle quality when
using a performance cam while still getting the benefit of the upper end power over a stock
cam. As the engine increases in RPM the Bleed down effect is reduced resulting in more duration
and valve lift. Having lifters with a much smaller Leak Down range will also balance all
of the cylinders to each other. Having one cylinder with lifters having a Leak Down of 80
seconds will react and produce a different power curve than the same cylinder with a 10
second Lifter..
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