[JLMounce]

Think of bleed down lifters as a precursor to variable cam timing. They effectively make the cam smaller at idle by bleeding off oil from within the hydraulic mechanism which allows the lifter to soak up some of the lift and duration.

The net effect is that you gain some torque and idle quality at idle and low revs, until oil pressure in the system and the speed of timing events increase to a point that overcomes the bleed of the lifters. At this point they are acting more like a regular hydraulic lifter and your cam effectively gets larger.

They are typically used on the RAIV cams in the community to get the performance of that large cam with a bit better street manners.

There's no real way to tell if those lifters are in your engine without pulling it apart. However, many people claim there is an audible clicking sound that they make.