Re: O/b vs I/b all things equal
...Theoretically a 2-stroke should burn twice as much fuel as a 4-stroke since a 2-stroke sucks and burns fuel every time the piston hits TDC, But they don't use as much fuel per burn so that offsets it a bit. I believe that a 150hp 2-stroke will always use more fuel making that hp than a 4-stroke will, but the weight savings of a 2-stroke again offsets it...
A 2 stroke
WILL theoretically burn twice as much fuel at the same RPM if the engines are the same
Displacement.
If they are the same
Horsepower, they will "Theoretically" burn the SAME amount of fuel.
A 200hp 4 stroke will be in the neighborhood of 4 liters of displacement.
A 200hp 2 stroke will be closer to 2 liters.
The two stroke will give you the same horsepower in a smaller, lighter, simpler, engine.
Its downside is that it does not operate with cam controlled valves like the 4 stroke.
With a 2 stroke the intake port and the exhaust ports are both open simultaneously during a portion of the cycle.
Intake and exhaust takes place at the same time, and a small portion of the intake Fuel/Air mix can pass straight out the exhaust port and burn in the tail pipe.
Some fuel is wasted in exchange for simplicity, size and weight.
If high power and fuel efficiency is the overriding factor, think diesel.
If operating cost and fuel efficiency is the goal, the 4 stroke is preferred.
If simplicity, size and weight are the big concern. The 2 stroke is indicated.
If fuel efficiency is of No Concern but small size and light weight are required. The gas turbine wins!
That is why you will only see Turbines in unlimited racing boats where operating cost are not a consideration.
Don't expect to see a Turbine in pleasure boat or a private vehicle unless the cost of fuel approaches Free!
The Government/Military loves Turbines, but they don't pay for the gas!