Variable hydraulic lifters for 440 engine

I guess I was being too subtle... obviously it's a bleed-down orifice. :rolleyes:
Thicker oil doesn't bleed down the lifter as fast. Thicker oil also causes higher oil pressure.
No, oil pressure does not directly cause a change to the bleed-down rate.

Anyway, a few people seem to like them and can live with the tapping at idle.