8) i think you are confusing a throttle stop with a rev limiter.
a rev limiter limits engine rpm to a set maximum. you can get them in single or multiple stages for various settups. a single stage limiter will allow the enginet o rev to, say, 6000 rpm +/- 100 rpm. that way you can keep you foot on the floor through a run and never over rev the engine when you speed shift, using the clutch and snapping off a shift as fast as possoble. if you a dual stage rev limiter, you can set one limt, say 5000 rpm for staging a turbo motor to build maximum boost, then when the clutch is released the second stage kicks in and allows say 6500 rpm. you can also set the rpm in which nitrous oxide kicks in. single stage rev limiters are usually legal in bracket racing, however some tracks dont allow dual stage limiters.
a throttle stop, usually illegal in most bracket classes, limits the amout of power an engine will make by closing a second set of throttle plates to choke the engine off above a certain rpm to prevent breaking out on a run. throttle stops are adjustable, sometimes even by the driver during a run, so you can take advantage of track conditions.