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2- vs 4-cycle motors
Those 2-cycle engines on trimmers and chainsaws are giving way to 4-cycle ones. Given the same displacement, do they have the same power?
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| | re: 2- vs 4-cycle motors
My buddy has a 4-cyl homeowner trimmer and it's a beast--stops at nothing.
By power I think we'd need to distinguish between torque and HP. I have to think the 4-cyl has more torque. And I be curious about usable RPM--trimmers and chainsaws seemingly would benefit from a 2-cyl.
But considering technology advancements that diesels have seen in recent years, diesels are on-par RPM wise with gas engines, so, conceivably, 4-strokes may someday seethe same lower RPM that 2-strokes do. Just my opinion.
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Light duty 2-strokes are simply not as efficient as 4-strokes, which pretty much levels the playing field from a power perspective. But I haven't seen a carbureted 4-stroke yet that will run upside down.
Unfortunately, I think it's the EPA that is forcing the shift away from 2-stroke applications. They think the silly "tamper-proof" carbs on these new fixed-rpm 4-strokes stop tinkering owners from increasing pollution levels. In my estimation, the power just isn't there anymore (compared to previous carb/throttle configurations). But back to oil burners. On heavier duty 2-strokes, the EPA's already mandated oil injection. That takes improper oil/gas ratios out of the equation. But owners that can still blend their own oil/gas mixture for lighter duty engines - remain beyond their control. EPA solution? Get rid of light duty 2-strokes.
//greg//
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Stihl makes a 4-stroke, called the 4-mix, that runs on 2-cycle mix for lubrication. Those run upside down and the dealer told me they had excellent power and meet EPA regs.
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Saw a show on Discovery or History about railroad locomotives. Some of them are two cycle diesel, don't remember why now if it was more power from the same displacement or more efrfecient fuel use.
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But I haven't seen a 4-stroke yet that will run upside down.
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I fly a plane with a 4 stroke engine certified for inverted flight, and I roll it over on a regular basis too! 
I agree though, the new small 4 strokes are very good, and only getting better.
Best of luck.
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yeah, but we're talking earth-bound carbureted engines Murf. Not fuel injected airbornes.
//greg//
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If I may re-word the question, it's time to replace my 31-cc brush-bladed rotary trimmer, and I need to know this: In a 4-stroke, would the same cutting ability go with a smaller, the same, or a bigger displacement? The answer from dealers depends on what they're selling.
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Auer;
Rather than me giving a shot in the dark answer about like dispacement engines being capable of like output being 2 or 4 stroke, somewhere some must have a rule of thumb chart about that.
My GUESS is that a four would be roughly half as capable, but not sure.
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| re: 2- vs 4-cycle motors
That's an interesting question and I have no idea what the rule of thumb might be. Two cycles don't extract as much power per power stroke due to more valve overlap but they have twice as many power strokes. Maybe the only real world specs that matter for hand held equipment would be power, weight and fuel consumption so displacement may be rather unimportant but I'd be curious to know the answer as well.
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