The Murphy Builders Site

Hi Paul

This stuff gets interesting. The 4 valve soob can get almost 110%
volumetric efficiency at 4400 rpm as well. That compares to around 75%
for a stock Lycoming. So that also magnifies the higher compression
efficiency. At 21"MAP I'm not really taking much advantage of that in
cruise but I'd guess my SFC at full power is dramatically lower than the
Lyc at full power and full rich. And of course with liquid cooling, the
soob (and maybe the rotax?) enriches very little at full power compared
to a Lyc.
Ken

C&P Kucera wrote:

I agree, fuel injection helps spread the fuel around so that it burns more
efficiently.
One other thing is having higher compression ratio, this has a big effect on
increasing piston engine efficiency, auto engines, Rotax, diesels are
designed to handle higher cr, Lyco,Conti, etc are not designed for it,
pressures and temperatures climb with higher cr, more energy is extracted
from same amount of fuel as the cr goes up.

Paul

453R

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