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9/22/2017 12:11:25 AM
Posted: 8/8/2005 10:30:00 PM EDT
Whats the difference? Thanks
Link Posted: 8/8/2005 10:32:42 PM EDT
[Last Edit: 8/8/2005 10:34:49 PM EDT by FredM]
One fires everytime the piston goes to TDC. One does it everyother time.


ETA:

TDC = Top Dead Center.

Plus there are numerous differences in fuel and air delivery systems.

As well as 2-stroke gets oil from fuel and not from a seperate system.
Link Posted: 8/8/2005 10:45:41 PM EDT
Link Posted: 8/8/2005 10:48:11 PM EDT

Originally Posted By Sylvan:
ultimately, a 2 stroke is twice as powerful as a 4 stroke of the same size.
When someone invents a 2 stroke without burning oil as part of the deal, they will be one rich mofo.
Anybody smart explain to me why this can't be done?




There are enviro friendly 2-strokes out there.
Link Posted: 8/8/2005 10:48:28 PM EDT
too much heat, you'd cook the valves, rings, and score the cylinder walls.
Link Posted: 8/8/2005 10:51:06 PM EDT
Link Posted: 8/8/2005 10:51:46 PM EDT

Originally Posted By Sylvan:
When someone invents a 2 stroke without burning oil as part of the deal, they will be one rich mofo.
Anybody smart explain to me why this can't be done?



two stroke diesel engines do not use an oil mixture in the fuel. But they do require a super or a turbo.
Link Posted: 8/8/2005 11:17:28 PM EDT
Theoretically, twice the power could be generated. But in reality, the breathing problems of most two strokes limits the output.

Now on the recent designs...one uses direct fuel injection which COULD theoretically be done oil-free. All two-strokes need some form of forced intake. Most gasoline engines use crankcase forced induction and this is where the oil comes into play. Forget what is commonly believed, that the oil in the gasoline makes the gasoline into a lubricant. It doesn't. What the oil does is what happens when it hits the normally war engine crankcase. The gasoline evaporates, leaving behind a thin film of oil, usually plenty for anti-friction bearings like ball, roller and needle bearings. It also is plenty for the piston ring lubrication without the need for oil control rings.

In regular two stroke engines, a small portion of the air-fuel mixture leaves the engine unburnt in the process known as scavenging. This happens when both intake and exhaust ports are open at near bottom dead center. Here, the crankcase is at highest pressure from the downward movement of the piston and closed reed valve. The exhaust port has just opened, dumping the still high pressure gases of combustion when the intake port opens. Fresh charge swirls around the combustion chamber, scouring the contents of burned gases and replacing it with fresh but in the process, some unburnt gas escapes.

Back to the latest two-stoke design. Direct fuel injection is the answer to most HC emissions. By injecting the fuel AFTER the intake port closes and scavanging with air only, the little oil mist from the crankcase is all that contributes to the HC emissions. Oil is still injected into the intake to lubricate the crankcase. This requires high pressure, DURABLE injectors and very precise computer controls. Just a step less than a diesel injection system but it still needs a spark.

How to make it better? Well, a supercharger could be used to isolate the crankcase from the intake but this isn't really needed. Closed lubrication system could be used, enabling a truely dry crankcase. Either way, replacing the anti-friction bearings with a full pressure lubrication system would make for a gain in durability. A supercharger would make the most sense...and the most power.
Link Posted: 8/8/2005 11:31:08 PM EDT
A 2 stroke can rev out much much higher than a 4 stroke. That's why you see them on chainsaws and such. They are also lightweight because of less parts. 2 strokes dont have any torque so they just die when at lower rpm range.
Link Posted: 8/8/2005 11:58:47 PM EDT
two stroke engines and 4 stroke engines are very diffrent but each has their own advantage.

A 2 stroke has very few moving parts, some 2 stroke engines only have about 5 moving parts. So you know 2 stroke engines have very high revolution potental, I know where to get a 2 stroke engine that revs upto 40,000 RPM, I have that engine, I also have an engine that was tested at reaching 38,000 RPM.

The highest Reving 4 stroke I've seen comes in about 15,000 RPM

also with a 2 stroke engine (older models) requires what's known as a tuned exhaust system (tuned pipe). The pipe adjust how the scavageing is done, at lower, mid or high RPM. Unfortunately the older model 2 stroke engines do have some serous design flaws.

In a perfect world 2 stroke engines would have the potental to generate 2x the power of a 4 stroke.

To my knowledge the 2 stroke was the first internal combustion engine.


4 Stroke engines are commonly more fuel efficent. Currently they have numerous moving parts that control when the valves are opened, closed, etc. 4 strokes are more difficult to opperate over 2 stroke.

With last years technology the 4 stroke engine generated more low end power.
A 2 stroke generated it's best power in low-mid on up RPM.



For vehicles like automobiles (lage engines) a 4 stroke is probably the best because of fuel efficency and low end power.

Yet for light vehicles/equipment that require light engines with high Revolutions per minute a 2 stroke is a good choice.
Link Posted: 8/9/2005 3:35:51 AM EDT
[Last Edit: 8/9/2005 3:37:52 AM EDT by TheOtherDave]

Originally Posted By madmann135:
two stroke engines and 4 stroke engines are very diffrent but each has their own advantage.



Yep.


A 2 stroke has very few moving parts, some 2 stroke engines only have about 5 moving parts. So you know 2 stroke engines have very high revolution potental, I know where to get a 2 stroke engine that revs upto 40,000 RPM, I have that engine, I also have an engine that was tested at reaching 38,000 RPM.


It's obvious that you are talking about model airplane engines here. You can't compare a gasoline powered enigine to one that runs on Alcohol, Nitromethane (lots of it in a 40krpm model motor), and about 20% oil content by volume in the fuel. You are comparing apples and pomegranates.


The highest Reving 4 stroke I've seen comes in about 15,000 RPM


In racing applications (at the 500cc World championship GP motorcycle races which were the last gasp for exotic 2 stokes) 2 stokes rev to only about 13-14,000rpm. They sound faster than that due to their exhaust note, but exhaust expansion velocity dictates the rev range. Since the pipe timing is partially responsible for the intake timing it doesn't make sense to run the enging faster than the fuel will explode in the exhaust..

As for 4 strokes, even garden variety 600cc sportbikes rev to 15,500 these days. The Japanese and European markets got 19,000rpm 250cc 4 cylinder bikes back in the early 90's. And Fomula 1 cars go higher than that.


also with a 2 stroke engine (older models) requires what's known as a tuned exhaust system (tuned pipe). The pipe adjust how the scavageing is done, at lower, mid or high RPM. Unfortunately the older model 2 stroke engines do have some serous design flaws.


The length of the pipe dicatates the RPM range it will produce power at. The volume and port timing are set to set to help that resonation (i.e. coming on the pipe).


In a perfect world 2 stroke engines would have the potental to generate 2x the power of a 4 stroke.


Close but not quite-you have seen power outputs for 4 cycle motors double reliebly in the last decade. 2 strokes have not managed the same growth. One reason for this is that 2 strokes are very difficult to use fuel injection, and a lot more finicky when playing with ignition timing. Both of those have been critical to the improvements 4 stroke power output.

For example, 20 years ago a healthy RG500 Gamma (4 cylinder 2 stroke streetbike that never came to the US legally) made about 80hp. They were fragile and unreliable, especially when modified. This gives them 160hp per liter which is great, but they had shitty gas mileage, poor driveabililty, and they burned every drop of oil you put in them. My 2005cc GSXR1000 makes 162hp, giving a similar power per liter, but it has midrange, emmisions controls, and it's as reliable as a stone hammer.

When you put the motors next to each other and see that the 2 stroke inhales every stroke, it is actually burning exactly the same volume of air/fuel as a 1000cc 4 stroke to produce the same power per liter, but is only able to match power at peak. As a 2 stroke lover it's hard for me to admit it, but mechanically opening and closing valves is the way to go.


To my knowledge the 2 stroke was the first internal combustion engine.


Nope, Mechanical valve actuation was first.

4 Stroke engines are commonly more fuel efficent. Currently they have numerous moving parts that control when the valves are opened, closed, etc. 4 strokes are more difficult to opperate over 2 stroke.

I guess it's debateable as to what's "more difficult" about operating a 2 stroke vs. 4 stroke engine, but with a 4 stroke you just put gas in it and go. On a two stroke you are adding or mixing gas, replacing rings, and fouling spark plugs on a regular basis.

There's more to the reason that 2 strokes aren't prevalent these days than just the EPA...

Dave
Link Posted: 8/9/2005 5:18:40 AM EDT

Originally Posted By VTwin60:
too much heat, you'd cook the valves, rings, and score the cylinder walls.



Think ceramics!!!!

Link Posted: 8/9/2005 5:30:48 AM EDT

Originally Posted By Loosin_It:
Whats the difference? Thanks



Here's something tarhead would say:

One lasts twice as long as the other
Link Posted: 8/9/2005 5:37:43 AM EDT
BOTH SHOULD BE BANNED!
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