Jabawocky
This is probably a more appropriate thread to discuss the rotax.
Rotax figures for the 912iS as per
http://fahrzeugtechnik.fh-joanneum.a...otax-912iS.pdf
show the figures of between .41 and .42 in cruise and .477 at full power
Performance
Maximum Power*
(5 minutes) 100HP / 73.5KW @ 5800 RPM
Maximum Power (sustained) 95HP / 69.0KW @ 5500 RPM
Maximum Torque 94ft-lb / 128NM @ 5100 RPM
If your Lycoming is returning .4 as you claim which I assume is LOP then the figures are almost identical given similar fuel management regime,
The operator manual for a 300 HP Lycoming IO-540-K, L, or M series engine shows a full power fuel flow of 24 GPH which is a BSFC of 0.474 ...
I repeat there is no such thing as a free lunch, the figures are almost identical. Considering you enjoy the advantages of scale and no gearbox losses it is a remarkable achievement for a little engine.
As for dollars per horsepower I agree the Rotax is more expensive and Rotax has become greedy but to be fair we are paying in euro exchange rates.
Aussie Bob
your argument re head temperatures is immediately proven wrong when you consider that a Rotax head operates at 85 to 95 c as opposed to 162 c for your heads. Add in thermal momentum for the liquid cooling = a more stable valve train. You might have got somewhere with arguments such as more cooling drag, increased complexity and weight but it is proven fact that liquid cooled engines enjoy more stable operating temperatures