<br /><br />regards<br /><br />Franki
<br /><br />Pressurized oil lubrication system. All bearings, valve train, piston parts, etc are continuously bathed and cooled by the oil, even at slow idle speeds. 2-strokes are lubricated by carrying the oil/fuel mixture by means of the crankcase pressure/ventilation circulation. This can be random with the fuel continuously washing the lubrication away. Less oil is supplied at lower idle speeds.<br /><br />No chance of oil injection system failure.<br /><br />Oil filtration system. Contaminates, wear particles, and dirt from air and fuel are filtered out. A 2-stroke has no way of filtering contaminates other than crankcase ventilation.<br /><br />Lower cylinder temperatures. Not only does a 4-stroke fire every 2 revolutions of the crankshaft rather than 1 of the 2-stroke, but fuel scavaging is minimized because of the valve system and valve timing. 2-stroke fuel scavaging (inherent to all 2-strokes) does not allow all the hot gasses (and unburned fuel) to escape the combustion chamber. Therefore, cylinder temperatures can't drop as quickly between strokes.<br /><br />And this leads to better efficiency from the 4-stroke. Not only because there is less wasted heat (energy) due to firing half as often and less scavaging, but because a 4-stroke usually allows higher compression ratios and leaner fuel/air ratios because the cylinder temps are lower. Inherently, 4-strokes will always be more efficient than 2-strokes. There is a correlation between efficiency and engine life. An engine that works less to provide the same efficiency will generally not wear out as soon.<br /><br />Fuel injection. As we know, directly injecting fuel into a 2-stroke is challenging. Again, mainly due to the cylinder temps, scavaging, and transfer porting. Electronics have helped this come a long way. 4-strokes have been proven as fuel injected since about the 1950's.<br /><br />Then we have exhaust. A 2-stroke requires a "tuned" exhaust system since exhaust pressure or resonance helps it make power. This is a major factor in performance. Unfortunately most 2-strokes don't have a variable exhaust pipe. They are generally tuned for only one operating rpm range. Tuned exhaust is not a concern on a 4-stroke because it has it's own valve timing absent of transfer ports. Efficiency and power can be maximized throughout the entire powerband.<br /><br />The only real disadvantage at this point to a 4-stroke is a little additional weight and a slightly higher initial price. The higher maintenance more moving parts won't last as long doesn't have as much power theory doesn't seem to be holding true.<br /><br />They're both good and both have their purpose. I've got both....but all my new one's are 4's. <br /><br />Point of the matter is.. you wanted to know if your four stroke would last.. Forktail has given you many reasons why it will.. (if it doesn't, he is the man to blame. <br /><br />As for the efficiency of 2 vrs 4 stroke.. I will make only one point.. <br /><br />(I get tired of arguing about this with mr Forktail quickly nowdays, he is the four stroke evangalist... and I can't stand up against that... <br /><br />If 4 strokes are so much more efficient then 2 strokes, why is it in motorcross engines, a 4 stroke must be almost twice the capacity of a 2 stroke to even be competitive???<br /><br />I agree with what he has stated about lubrication but the point of the matter is that there are many many non presurised lubrication <br />2 strokes with many many hours on them still working just fine. for that matter, a few thousand motherbikes as well.<br />So the arguement is really sorta moot.<br /><br />As I said, look after it, It'll be fine, go enjoy it.<br /><br />rgds<br /><br />Frank and last time I checked, those things have alot more then one gear to lessen the load..<br /><br />Also, they are not ALWAYS going up steep hills, and they don't often cruise at 5100rpm for long distances...<br /><br />Marine applications are VERY hard on engines.. 2 or 4 stroke.. so much so that sticking a standard Auto V8 into a speedboat with no internal changes, usually results in a quickly distroyed V8 in need of a rebuild... (seen that many times)<br /><br />So any car comparisions are invalid.. (I have heard all the experts on this very list give that very observation many a time.)<br /><br />The closest arguement to a land vehicle would pobably be motoX bikes (much higher rpms for sustained periods) or snowmobiles.. (can't comment on the later as it doesn't snow here much (at all)) but the load of pushing though snow would be pretty consistant I imagine...<br /><br />Anyway, I love both.. if I was boat racing, I'd have a 2 stroke, if I was having a lazy stroll to a fishing hole, I'd take a 4 stroke.. (thats my current opinion based on current models, it may change after new models come out.)<br /><br />rgds<br /><br />Frank<br /><br />PS, please don't ask that question anymore, I always feel the need to stick up for the underdog... 
You know I love 2-strokes. Is there supposed to be just one side (your side) to these discussions? Your perception of me is inaccurate....maybe it's you who is the 2-stroke evangalist?<br /><br />"If 4 strokes are so much more efficient then 2 strokes, why is it in motorcross engines, a 4 stroke must be almost twice the capacity of a 2 stroke to even be competitive???"<br /><br />Franki, to make these comments first you have to understand engine efficiency. It doesn't have much to do with displacement.<br /><br />Engine efficiency can be broken into two parts.....mechanical efficiency and thermal efficiency. Thermal efficiency is basically how much energy (from the fuel put into the engine) is converted into useful horsepower. Mechanical efficiency is based on the relationship of power developed within the engine, and actual power delivered at the crankshaft.<br /><br />Even volumetric efficiency isn't necessarily displacement based. It's based on the engines ability to intake the fuel/air mixture, not how much room (displacement) it has.<br /><br />Practically speaking with outboards, efficiency can be understood by how much hp is produced by the outboard per some amount of fuel.<br /><br />There is no doubt that a 2-stroke produces consistantly higher cylinder temperatures. Again this is because it fires every revolution. And there is no doubt that fuel scavaging will take place due to the cylinder porting, causing some of the unburned fresh intake fuel charge to be forced out the exhaust. These are just some examples of why the 2-stroke is knowingly less efficient.<br /><br />So ask yourself why Yamaha's 2-stroke 115 hp is 1730 cc's and their 4-stroke F115 is 1741 cc's? Or why the 2-stroke 200 hp EFI is at 3130 cc's and the 4-stroke 200 EFI is at 3352 cc's? The agrument of twice the displacement doesn't seem to hold true. <br /><br />"I think longevity is a useless arguement with regards to outboards..."<br /><br />Huh? I've used outboards to make a living commercial fishing, chartering, and for personal fun. Last I counted I own about 14. Who knows how many my business has replaced. The hours on my engines can add up quick. I've replaced many 2-strokes with over 2000 hours and some with near 3000. This is awesome. But I've consistantly run the 4-strokes longer and with less maintenance than my 2-strokes. Resale is better. Overall expenses are less. Overall confidence and enjoyment are a 10. I've got some 4-stroke 50's and 9.9's with over 4500 hours. My fuel injected F115's and 225's seem even better and I plan on keeping them past 5000 hours. Longevity important? You bet! My experience with both is proof enough for me.<br /><br />"No matter what Forktail tells us about how trucks with 30 wheels pull big loads up steep hills, the simple fact is that its not a valid comparison..."<br /><br />This comparison was only in response to another member's comment that 2-stroke outboards are under so much more stress than 4-stroke engines. I try not to initiate automotive comparisons or motorcycle comparisons or racing comments. But I will state the facts and at least the other side of the story. <br /><br />Relax Franki...this is not an argument, it's a exchange of information. I don't really care what other people run on their boat. And any experience I have to offer can be taken with a grain of salt if you wish. <br />an different load entirely to a boat.. but an extremely high one nevertheless..<br /><br />Nearly everything that has made a 4 stoke efficient can be added to a two stroke, and no doubt will be one day.. (I think thats Bombardier's plan..) positive lube, intake valve (with precompressor to replace crankcase compression). everything can be added bar the extra stroke... There are already variable exhaust ports on 2 stokes to increase efficiencey, how long before variable expansion chamber exhaust???<br /><br />My point is.. its modern technology that is making 4 strokes competitive weight for HP. As jimd said.. VTEC, DOHC etc... <br /><br />Apart from DFI... that kind of technology has not been added to the marine 2 strokes yet.. they are still much the same looper design as the 80's models.. <br /><br />Give it time.. it will happen.. in the mean time, if you have a boat capable of handling the weight difference, and holeshot and top end is not your ownly reason for having a big OB, then get a 4 stroke....<br /><br />Jimd, good point about tuned extractors on 4 strokes.. I had forgotten about that...<br /><br />Sorry for cluttering up someone elses post with an Off Topic discussion...<br /><br />rgds<br /><br />Frank
