George.... the O-340 has less displacement than the O-360, but the same bore.
It has a stroke in-between the O-320 and O-360 of 4.125 (O-320=3.875, O-360=4.375)
The weight appears to be much nearer the O-320 than the O-360 at 250 pounds, and, I'm guessing, given the weight, not quite as wide as the O-360.
More info is here... lots of engine info... gil in Tucson
http://home.adelphia.net/~aeroengine/Lycoming.html
------------------- from the web site ----------
O-340 -- {5.125 / 4.125 / 340.4} / {130.2 / 104.8 / 5578}
Same bore as O-160, O-320, O-360, O-480, O-540, O-541, O-720.
4cyl; O-340; 160-170hp@2700rpm; 1954-1977; Wt = 247-250#; TC = 277 on 7/20/54.
AY60; J56-57toJ76-77; S; W56toW62-63.
Applications: (US) Peterson Super V (Beech 35 Conversion to twin); Riley Twin-Navion; Thalman T-4.
4cyl; VO-340; 162hp@N/Arpm; 1954-1965; Wt = N/A; TC = none.
J57-58; S.
Applications: (US) Brantly B-2 (second prototype).
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