Re: Buy outboard before 2006 requirements?
miloman, did you help Evinrude do the comparison testing? Cool!<br /><br />You commented that a
"2 stroke is equally as efficient as a 4 stroke." I assume you mean just the outboard industry? It seems like the outboard industry is doing everything possible, and trying in every way, to make the 2-strokes more efficient. And doing a good job too! But all the time the 4-strokes seem to just plug along without efficiency concerns. My point is that the 4-strokes seem to have a lot more room for improvement with many untouched areas of ways to make those improvements. Whereas the 2-strokes seem to be pushing the limit. 2-strokes are incorporating cutting edge technology (while it's being developed) to make such claims as keeping up with the 4-stroke, while the 4-stroke outboard industry has yet to explore many other technologies. 4-stroke outboards really haven't changed since the 70's. For example, 4-stroke
cam-less engines are successfully being developed in the auto industry. 4-stroke high pressure split-shot fuel injection systems have been produced in autos for a long time. Lightweight sump-less 4-strokes are showing up in snowmobile technology. Emissions in 4-stroke automobiles is practically zero. Outboards haven't needed to go there yet.<br /><br />What will come of the 2-stroke after 2006 when things get even more strict? And after that?<br /><br />IMO, there are inherent flaws and limitations with a 2-stroke that will eventually cause it to lose out to the 4-stroke. This is very sad. I love 2-strokes. <br /><br />One of those flaws is the fact that the 2-stroke fires every revolution of the crankshaft whereas the 4-stroke fires ever other. Good news for the 2-stroke is that this produces more power per cubic inch of displacement. Bad news is that, although the 2-stroke is firing twice as often, it does not produce twice as much power. You'd think it should, but it doesn't This is because of another flaw of 2-strokes, excessive fuel scavaging, that results in inefficient fuel/air charging into the cylinder (raw fuel sucked through the intake port gets pushed out the exhaust port before it can be ignited). A conventional 2-stroke puts out about 20 - 60% more power than an equivalent sized 4-stroke. About 30% of the fuel/oil mixture enters the exhaust before it is burned. Additionally a portion of the burned exhaust gas remains in the combustion chamber during the next cycle, taking up room for the next fresh charge. Efficiency is lower than expected, at least compared to a 4-stroke.<br /><br />Now the direct injection and Ficht 2-strokes help solve fuel scavaging by directing high pressure fuel directly into the cylinder after the exhaust cycle, which helps a lot. But it does not make them "efficient" per say. Direct injection or not, 2-strokes have a higher frequency of combustion (firing every revolution). This creates higher average heat transfer rates from the cylinder...another flaw. Higher heat transfer means less efficient, and wasted energy.<br /><br />The higher combustion frequency of 2-strokes also creates higher temperatures and thermal stresses in the cylinder compared to 4-strokes, especially in the head and piston crown area. This is why you will find many powerhead failures in 2-strokes due to siezed or "blown" pistons and leaking head gaskets. Not so common with the 4's. Direct injection 2-strokes run even hotter in the combustion chamber, and typically need more lubrication (oil). Ironically, most direct injected 2-strokes inject oil directly into the crankcase, not the cylinder.<br /><br />Another flaw with the 2-stroke is it's inability to control exhaust timing. Much of the intake and exhaust cycle in a 2-stroke is dependent upon exhaust resonance (back pressure) to obtain the next fuel/air charge. Without some way to regulate the size of the exhaust port a 2-stroke can only maximize efficiency at one particular rpm. It is a sacrifice throughout the rest of the powerband. Less efficient.<br /><br />In my opinion, the real advantage to 2-strokes over 4-strokes is not efficiency, durability, or servicability. It is strictly power to weight. Weight. And the 4-stroke market is closing that gap quickly.<br /><br />As for where does the oil from a 4-stroke go? Mine gets recycled at the landfill's oil recycle station...for free. Same as everyone's auto. A better question is, "how does that 2-stroke oil disappear like that....is it magic? Hey, what's that smell?"<br /><br />Much credit is due to the direct injected 2-strokes. But in giving that credit, many people misunderstand or ignore how fabulous the 4-strokes are in design, and where technology will lead them as well.<br /><br />
