That quietness is deceptive because the SXV 450 is surprisingly powerful. Aprilia claims 60 bhp (70 for the 550), which is 10 or so more than a comparably sized single. The thing is, it doesn't feel that strong. Roll on the throttle at a corner exit and the power comes in small traction-producing pulses, as opposed to the big traction-disrupting bangs of a single. It doesn't tend to wheelie like a single, either, it just drives, drives, drives. Hold the throttle to the stop, let the revs rise to the 13,000-rpm redline (titanium valves, dontcha know) and there's very little vibration despite the lack of a counterbalancer. Statements about speed are largely irrelevant at a go-kart track, but the SXV was able to reel in all but the fastest 450s and 525s on the straights.