We've discussed it before at length - The traditional aircraft engines rule the roost in the 150-200 HP class.
We have, and you're right - in principle.
It makes no sense to take a fairly heavy configuration (V-8) and try compete at that power level. The only place where a V-8 starts to make sense is 300HP or more. Of course the V-8 can be made to run at 180 HP, but at that point its just a science project, not a valid powerplant choice from a requirements standpoint. Such an engine would have about as much practicality today as an OX-5.
But I have to disagree a little. :nervous: All that you've said is true for airframes that were designed for Ly/Con engines, but it isn't so true for airframes designed for a heavier engine. Take the Percival Vega Gull:
Percival Vega Gull
(Gipsy Six power) 1510lb useful load, 1020fpm, 660mi range
its engine had a 2.34 lb/hp ratio versus the o360's 1.43 lb/hp ratio, and yet it was and is still a good performer.
The Model A powered Piet isn't nearly as practical, but it does fly, and its engine only has a 5 lb/hp ratio. I think that any engine with a weight/power fraction below 3 lb/hp can be a useful powerplant in an airframe designed for it. Take the Vdub conversion, a 50 hp VW in a Teenie Two will have 2.9 lb/hp and works well because it was designed for it; the Tipsy Nipper is the same, as is the Jodel D.9 Bebe, and the Druine Turbulent.
Some examples,
Lycoming 0360: 1.43 lb/hp
gipsy six: 2.34 lb/hp
Wright J-5: 2.36 lb/hp
All alloy modular v8: 2.50 lb/hp
Iron SBF 5.0L: 2.92 lb/hp
Pietenpol model A: 5.00 lb/hp
Caveat: Of course, if you take a Vega Gull and put in an engine with a 1.43 lb/hp ratio, you still win. All I'm saying is that an auto conversion can be useful and economical if done right...
P.S., one bright spot with these modern auto engines is the ignition system, they are very reliable.