looking at the 360`s operators manual i have an hard time to understand pages 3-18 and 3-19.
so far my understanding was that specific fuel consumption (pounds per horsepower for one hour) decreases when you lower the RPM. lower RPM's result in less internal engine friction and less volume of air has to be pumped through the system.
but the manual shows clearly that the curves for the different RPM's have a wavy shape and come closer together when power output gets lower. at 40/45% power or so the lines even meet. if we just follow the curve for 2400 RPM the difference is very significant (0,43 for 75% and 0,58 for around 40%).
why do the lines meet at low power? is that caused by part throttle pumping losses at lower manifold pressure?
the graphs show that for full rich and fixed timing. would leaning and electronic ignition change the behaviour in general?
edit: i just discovered that my heading is misleading. it should read: "why is specific fuel consumption at different RPM's equal at low power settings?"