Not many competition .21 off road engines produce that kind of power, more like 2.5hp @ 30,000 + rpms. Circuit engines are another kettle of fish. 2.9hp @ 28000 seems pretty decent for a MT engine. That said, there quite a few MT engines reputed to put out well over 3.0hp according to the manufacturers claims. Most times though these figures are quoted at RPMs that simply aren't realistic for real world conditions.

Competition .21 engines are much more expensive than .28 - .30 size MT engines and have power/torque curves that suit lighter machines.

There aint no replacement for displacement!