My .28 claimed 2.8bhp. It was kinda frighteningly quick, especially the mid range acceleration. Very seldom got it up to full flat out speed and only then in longish grass.
My Picco .21 claims 2.1bhp, but it's far more immediate to respond so sharper at low speed. Still haven't tuned it yet to find out what it's top end is like.
Generally the only reason these tiny engines produce the same kind of horse power as a 50cc motorbike/scooter is the insane RPM they produce (and of course nitro is much more bang per cc)
Power = Torque * RPM * FACTOR <- the factor depends on what units you use.
The more displacement you have, generally, the higher the torque, but at a cost of some RPM.
With a fairly average .21 able to light up the wheels from stand still of a buggy on dry tarmac more torque would be more or less a waste.
.46 is going to weight quite a bit and if the engine is not mounted far enough forward could make it wild tail happy and hard to balance in jumps.