The most efficient to date is a 2-stroke design. it is a turbo desiel 2-stroke.
but normally a 4-stroke is usually the more efficient of the two engine types.
Valves
A four-stroke engine runs cooler than a two-stroke engine primarily because it has a more efficient cooling system due to its longer cycle, which allows for more complete combustion and better heat dissipation. In a four-stroke engine, the intake, compression, power, and exhaust strokes are separated, giving more time for heat to escape during the exhaust stroke. In contrast, a two-stroke engine fires once every revolution, leading to less time for heat to dissipate and often resulting in higher operating temperatures. Additionally, two-stroke engines typically mix oil with fuel for lubrication, which can also contribute to increased heat generation.
A two-stroke engine pollutes the air more than a four-stroke engine primarily because it completes a power cycle in just two strokes of the piston, allowing for less efficient combustion. This design often results in unburned fuel being expelled with the exhaust, leading to higher emissions of hydrocarbons and other pollutants. Additionally, two-stroke engines typically lack sophisticated emissions control technologies, further exacerbating their environmental impact. In contrast, four-stroke engines have a more complete combustion process and usually incorporate systems to reduce emissions.
Two-stroke engines generally pollute the air more than four-stroke engines due to their design and operation. In a two-stroke engine, the combustion cycle is completed in just two strokes of the piston, which often leads to incomplete combustion and unburned fuel escaping during the exhaust phase. Additionally, two-stroke engines typically mix oil with fuel for lubrication, resulting in higher emissions of hydrocarbons and particulate matter. In contrast, four-stroke engines have a more efficient combustion process and separate lubrication systems, leading to lower emissions.
A 2-stroke engine makes power every2 cycles were a 4-stroke makes power every 4.Hence 2x power. This is absolutely INCORRECT! A two stroke engine develops it's PEAK horse power twice as fast as a four stroke for the reason given but that is it. For a given displacement a four stroke engine will ALWAYS make more torque and horsepower than a two stroke engine of equal displacement. This is due to the fact that a four stroke engine cleans the cylinder of contaminated (exhaust) air, compresses the air/fuel to a more efficient level, and draws a cleaner air/fuel mixture into the cylinder as there is no slow burning, air/fuel mixture contaminating oil mixed in the combustion charge. I have over forty years experience working on engines, and can tell you, the ONLY reason two stroke engines have lasted this long, is due to the fact that they weigh less than an equivalent horsepower four stroke engine. If they DID develop more horsepower, the four stroke would not have become the standard internal combustion engine used in transportation, generators, air compressors and the like.
Unless we are talking about big diesels - Yes.
Yes, "four cycle" and "four stroke" are the same. The two terms may be used to describe an engine. As a rule, the term "four stroke" is more commonly used.
Four stroke engines must have at least 2 valves: one exhaust and one intake. Most modern engines are going to 4 valves per cylinder to allow the intake and exhaust strokes to be more efficient.
Most small engines are two stroke because you can get more power from a smaller engine with two stroke rather than a four stroke engine. It takes less to cool and to operate the engine.
2 stroke means it takes two strokes for a power stroke and 4 sroke takes four strokes for power stroke so in otherwise 2 strokes are way faster and more torqey
A four stroke engine contains a lot more rotating parts. Four strokes contain one or more camshafts, cam gears, and a timing chain. All of which cause more rotating resistance (mass) than a two stroke has. A two stroke has none of these rotating parts, therefore, it rotates more easily when kick starting. Also the two stroke fires (sparks) twice as often (per revolution), than a four stroke, doubling your chances of getting spark (ignition) during the kick starting process.
They are - most inboard engines are 4-stroke. But as with land vehicles, you can get a smaller engine with 2-stroke (or more horsepower with a smaller engine) so the small engines like some outboards tend to be 2-stroke.