there is an engine rpm limiter to prevent over-revving on acceleration, every engine has one these days.
They will limit revs when you are neutral to about 4000 rpms, and won't let you rev higher than that when you are in PARK OR NEUTRAL. When you are in drive you should be able to rev right up to the limiter, which is somewhere around 6500 rpms or so, can't remember the exact number, but it is much higher than 4k. | 
