Are 4 strokes as tough as 2 strokes?

[Forktail]

Re: Are 4 strokes as tough as 2 strokes?

No problem Franki. But if someone here cries "misinformation" they better have something to back it up with. <br /><br />I think you got off on a tangent with the AETC, motor-X, single cylinders, holden V-8's, and automotive comparisons to justify your argument.<br /><br />"they didn't settle on those capacities to beat the 4 strokes.. they did it because a 2 stoke loses less power then a four stroke (every stoke is a power stoke and no cam/valves to move around at high speed.)and that they don't need to be any bigger.. you make it sound like they are designed to rev their rings out all the time to do anything useful.. we know thats not true.... also, last time I checked, the WOT on the four strokes seems to be higher then the two's...."<br /><br />A 2-stroke does not lose less power than a 4-stroke because it fires every stroke. Stroke for stroke, a 4-stroke will produce more power. The 2-stroke is less efficient. As I've said before, firing every stroke actually causes the engine to create and lose more heat. It limits compression and lean fuel/air mixtures because of the cylinder heat. And this reduces the 2-stroke's efficiency. 2-strokes fire twice as often, but are nowhere's near twice as powerful as a similar displacement 4-stroke. Efficiency.<br /><br />Yes, WOT rpm is generally higer with 4-stroke outboards. I've said this before. Ask yourself what limits rpm in a 2-stroke outboard? Scavaging? Heat? Of course.

 

[Franki]

Re: Are 4 strokes as tough as 2 strokes?

Yep, I go off on tangents,, its a problem of mine.. I am seeing someone about it... <br /><br />Ok, assuming I go along with all of that.. and we assume that a four stroke has much more efficiency then a two stroke.. <br /><br />Why are two strokes without an optimum expansion chamber (whats in the leg can hardly be called optimum.) somehow keeping up with the four strokes at all cc for cc...<br /><br />by your analogy, the four stroke should be miles ahead at the same capacity.. because of lower compression, more wasted energy etc etc...<br /><br />There should be no comparision at all, and yet there is..<br /><br />1. Even people tha don't work for big B will tell you there is not alot in the fuel usage between ficht/Optimax and 4stroke... <br />2. Two strokes are consistantly smaller cc for the same power. (albiet not by much in outboards.)<br />3. There are very aggresively tuned production 2 strokes that can rev up to around 11000 rpm and produce most of their power up there..without frying.. (Theres that motox thing again,, sorry.) so why haven't they self destructed if heat is the reason they can't rev out..?<br />4. Firing Stroke for firing stroke, a four stroke definately gets more bang for its buck.. but there are half as many.. otherwise the 4 stroke would totally obliterate the 2's,,, <br /><br />Anyway.. lets shake hands and call an end to this.. I conceed some of your points.. and thats enough..<br /><br />Lets have half this conversation again in 2 years.. see what these E-tec things add to the equation.. <br /><br />rgds<br /><br />Franki

 

[JS2]

Re: Are 4 strokes as tough as 2 strokes?

An oil injection system in a 2 stroke can't fail when you don't have one - that's why I stick with premix. The 1969 Suzuki T250 motorcycle in my garage has a 2 stroke engine that still runs good. So much for needing a pressurized lubrication system for longevity.

 

[Forktail]

Re: Are 4 strokes as tough as 2 strokes?

"An oil injection system in a 2 stroke can't fail when you don't have one"<br /><br />In case you haven't noticed, most 2-stroke outboards do have an oil injection system. And disabling the oil injection system on some of these outboards can seize the oil pump due to lack of lubrication. This can ruin the entire outboard, pre-mix or not.<br /><br />"that's why I stick with premix."<br /><br />Yep. Nothings more fun at the fueling dock than measuring oil, counting the ounces and partial gallons. Lets see, do I put the oil in first and guess at how much fuel I will need to add so it gets all mixed up? Or do I add the oil last based on how much fuel I put in, hoping it mixes itself later. And didn't I add a little extra oil last time...or was that two trips ago? <br /><br />"So much for needing a pressurized lubrication system for longevity."<br /><br />Yea, really. I see no advantage to a pressurized lube system. Especially with that filter and all. Why don't 4-strokes just use pre-mix too? .<br /><br />To even hint that a pre-mix lube, which is washed down with gasoline and randomly distributed to the engine, is better than a pressurized oil system is laughable.

 

[jsimpson]

Re: Are 4 strokes as tough as 2 strokes?

Melloyello, I'll answer your question about two-stroke advantage in motocross. Four strokes are vastly superior to two strokes in every respect except power to weight ratio. In motocross, nothing is more important than power to weight ratio, so all else can be sacrificed for it. A better example would be an airplane engine (all of which are four-stroke). While power to weight ratio is certainly important, reliability, longevity, durabilty and fuel economy are more important, so four strokes are nearly universally employed. In boating, reliability, longevity, durability and fuel economy are more important to me, hence my choice is four stroke for offshore or for Everglades.

 

[Simoniz]

Re: Are 4 strokes as tough as 2 strokes?

Forktail and Franki, Have you ever thought of putting in a paragraph break in your posts? It makes them so much easier to read.

A marine engine always works much harder than an engine in an automotive application. The reason is that the car engine has a direct mechanical conection to the road. A marine engine has no direct connection to the water, ie the propellor will always turn at the optimum speed for the power supplied.

To understand this, imagine a car being driven at 70mph on a flat road with the engine turning at 3000 rpm. The throttle position required to achieve this is probably not very far open as, once the car is moving, the rolling resistance is quite small. If the road begins to slope downhill, the same speed is maintained with less and less throttle until the engine is operating under zero load conditions. The boat engine however is working at its maximum capacity for that throttle opening - it has to be. If there were any spare it would rev higher and the boat would go faster. The analagy that the boat can go downhill and the engine run at idle or under a light load condition does not exist. For the car engine to work as hard it would have to be driven up an endless steep hill with at least 1/2 or 2/3 wide open throttle.

Its the same with an aero engine (with a propellor) the air / water absorbs all the power that the engine produces.