Torque is a better indicator for engine selection versus displacement only if the curve itself is published (this is not very practical marketing-wise). The quality of the curve is what is most important (not peak torque). For example, an engine with a peak torque too close to the operating RPM can have problems snubbing out when it is overexerted. Or if an engine has a very peaky torque curve it will not hold the line well. The Tecumseh L-heads (318cc and 358cc) have a very flat curve that peaks down around 2500 RPM which is beneficial. The Briggs model 15 (249cc), which is market-wise comparable to the 318cc Tecumseh L-head, has near comparable peak torque but nowhere near the quality of the torque curve. The higher average torque across the RPM range of the Tecumseh is (in this case) mostly a result of a 28% displacement advantage.
As an engineer I know a little about torque curves.
Measuring an engines performance based on displacement is analogous to doing the same based on it's color, or it's dB rating.
For all engines or class of engines produced a corresponding performance curve is also produced, you know. . . that physics thing again.
And on performance curve there is and will always be torque = force at a specific rpm and work in a unit of time which is hp. I do not think this is likely to change.
Sales, Marketingand OEMs may chose to intrepret these performance curves disigenuously but to me "when in doubt, look at the curve"
