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What they do ....
When you shut off the engine there is typically at least one valve that is hung open. When the valve is open the spring keeps pressure on the valve train. This pressure causes the lifter for that valve to bleed down, just like when adjusting pushrods. This changes the timing for that particular valve when the engine is first started, until the lifter pumps up. Depending on the build specifics, like compression, cam timing etc. this can effect starting and other things. The more the lifter is allowed to bleed down, the more it effects the timing of the valve. In more aggressive builds with more aggressive cams and compression, limiters can be installed in the lifter to limit the amount of bleed down to prevent this from happening. With a standard .100" adjustment, the lifter can bleed down .100" before bottoming out. That means higher cylinder pressures when starting before the lifter pumps up.
The theory behind the limiters...
Adjust the pushrods until they bottom out (with limiters installed). Then back off a couple wrench flats. This only allows the lifter to bleed down a few thousandths when not running. When the engine is running the lifter still acts like a hydraulic and as the engine expands, it compensates with the cushion of oil. Another thing the limiter does is to stop the lifter from collapsing at higher RPM's. It acts like a solid lifter. This becomes more evident when using heavier valve springs for higher RPM's.
Are they louder....
I have never run them myself so I can't tell you from experience. But in theory they should be louder whenever the lifter plunger is on the limiter. At higher RPM they should be louder as well since it would stand to reason the plunger would hit the limiter on every valve open event and lift off it during the close.
IMO, there would be no reason to run them in a mild street build.
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What do I know, I ride a Shovel
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