I'm looking at an add for it right now in Radio Control Car Action magazine. If the specs in the ad aren't an exageration and a race tuned engine will survive 7.5 gals then it sounds like an engine worth looking in to. These are the specs from the ad:

O.S. .21 VZ-B V-Spec-T (P)

Displacement: .21 cu in (3.5cc)
Bore: 0.653 in
Stroke: 0.630 in
Practical RPM: 3000-40,000
Output: 2.5 bhp @ 33,000 rpm
Weight (W/O muffler): 12.7 oz (360g)