Perhaps, a new engine is required for our needs. New engine designed specifically...

[djmsgstride]

If some tool and die firm connected with a foundery in the USA could make an aluminum/magnesium alloy engine casing designed to house a crank (E4340 forged steel of course) with a 4.00 inch stroke, having 1 inch wide bearings, a mechanical oil pump, a high lift/long duration cam with pressed timing gear, and using a magneto ignition (EI and EFI optional), we would have the beginnings of the type of engine the LSA/air boat folks need, and a new, completely different power plant designed to support this sport industry, made in America. I think a two cylinder air cooled version could meet the 100 lbs requirement; a four cylinder version could range between a 140 lbs. to 160 lbs. weight requirment. Both would have 4.00 inch cylinders, for a rating of 55 h.p. (3 gph) and 110 h.p. (6 gph) @ 3200 rpm power output respectively. No reduction drives required.