Two Stroke vs Four Stroke?

[kd6nem]

Re: Two Stroke vs Four Stroke?

If the oil doesn't get to the water in a DFI two stroke WHERE DOES IT GO? Yo DO have to keep oil in the oil reservoir, since it does keep pumping it into the motor, right? I thought a main advantage was that it was efficiently applied and did not require as much oil, not that it didn't release any at all.<br /><br />Honestly, I'm not all together up to speed on DFI. Doesn't the air still go through the oil misted crankcase before if moves through the intake port, or is there a newer & better way to move the air into the combustion chamber during the intake cycle? Only other way I can imagine would be use of a blower, unless using four stroke technology. But as I said I haven't studied these new two strokes in any detail and haven't yet stumbled across any good explanation of their theory of operation. I'll be happy to be enlightened here.<br /><br />I agree that adding a catalytic converter would be a total nightmare. But I still don't see why all EFI four strokes can't at least equal an E-TEC for emissions with just a little factory tuning. Four strokes have been run clean for many years now- that part is not new technology, although the levels acheived y the E-TEC are most impressive. I still wonder what total cost of operation will be five years from now on these. Time will tell. I hope they prove to be all that is claimed. It sure does look like a very nice although rather expensive package.

 

[TOHATSU GURU]

Re: Two Stroke vs Four Stroke?

Many four-strokes are "Three Star" rated for emissons such as the E-tec's are. As more mandated requirements go into effect the emissions levels will drop on new product.Your all talking about meaningless differences in micro measurements...except that 4-strokes produce huge amounts of CO2(that's why the EPA and CARB are pointing at them now) and the only way to get rid of that is with catalytic converters( today's technology for CO2)

 

[Bwalker]

Re: Two Stroke vs Four Stroke?

"If the oil doesn't get to the water in a DFI two stroke WHERE DOES IT GO"<br />It is combusted.<br />The as of now not even efi fourstrokes can match the emmissions levels of a E-tech. Two strokes have some advantages when it comes to CO and NOX emmissions based on their design. I might also point out that not only is the E-Tech Direct injected, it also has stratified combustion which is just as important from a emmisions standpoint.

 

[kd6nem]

Re: Two Stroke vs Four Stroke?

Elvin,<br />I believe you must be referring to CO not CO2. If it burns with air then it makes co2, regardless of two stroke or four. Cat won't fix that. In fact a cat tries to make co into co2. If the EPA wants to outlaw CO2 then we should outlaw politicians- they gas out with more CO2 than anything else! And I agree that most of the differences in levels are pretty meaningless.<br /><br />Ben,<br />OK, I'll buy that the oil is cleanly combusted.<br />I am impressed with the E-Tec, don't get me wrong. It is a true engineering marvel- a real breakthrough in that it is the first to bring its technologies together so successfully. But how is it that the E-Tec is so vastly cleaner than anything else? Is it really? The NOx advantage from two strokes must be a result of lower compression ratio or retarded timing, more the former than the latter I suspect. Anyone have any specs for comparison? Normally this would mean less fuel efficiency, although this seems to have been worked around a la Honda's old CVCC stratified charge (well, not exactly Honda's method in this case, but Honda was among the first to make the idea commercially viable) and very efficient injection/combustion management. I understand the ultra clean two strokes live their entire life a hair's breadth away from total meltdown to accomplish this so I still wonder about longevity. (run very lean while still with as advanced spark timing as they can possibly get away with, yet no cooling oil sloshing under the piston, only the intake stream. Requires a special eutectic alloy for the pistons) I do not know about the CO difference, although modern four stroke technology remains remarkably clean in this regard. As I stated before, it would only take some minor tweaking for factory engineers to raise the bar once again with the four stroke, hopefully even without adding a cat. And even if they do? Might be a little added expense and an ugly wart hanging out the back of the motor. Bottom line is the same can be accomplished with a four stroke with fewer gymnastics than a two stroke. Just because it hasn't been fully done in outboards doesn't mean it can't be or won't be. It HAS been done for automotive engines which still have superior emissions compared to E-Tec. But aside from the sleight of hand tuning techniques on E-Tech (which are valid & DO make a difference), combustion of hydrocarbons under pressure still boils down to combustion of hydrocarbons under pressure. I still do not believe that the two stroke has any inherent magic which will make for a cleaner engine. It is just that Evinrude has poured a LOT of attention and resources into it and has done an excellent job with it. And they too will eventually be looking at catalytic converters also as standards keep getting arbitrarily raised! But given the added complexity of these new motors, the benefits of owning a two stroke compared to an equally refined four stroke are growing smaller as compared to years past (IMO only Verado is "equally refined" albeit with a different emphasis, although I'm not sold on it yet either). I believe the four stroke cycle will eventually prove to be at least equally viable if not hands down superior in the future. But then I could be wrong. This part of history has not been written yet, although we do see that the two strokers have risen to the occasion most admirably! Just don't count the four strokes out yet. As with past examples of two strokes, past mediocrity in recent four strokes does not necessarily equate to a mediocre rendition in the future. They deserve a chance to be further updated & further refined just as the E-TEC has so wonderfully been. I remain unconvinced that the outboard makers put every effort they should have into their four recent strokes. Had they started where Fisher Pierce left off the level innovation would have been much greater. It took Honda another ten years to even think about equaling the Bearcat in terms of reliability and weight, and this after buying a few to study.<br /><br />By the way, is anyone "taking bets" on when Detroit will start putting E-Tec's under the hood of cars? The way some talk this must be inevitable since the four stroke is obviously doomed, the two stroke is obviously superior in every way! (sarcasm intended) Actually back in the 70's some wiseguy took I believe a big Merc powerhead and radiator in a baja racer and womped all over the air cooled VW powered ones, although using at least twice as much fuel to do so. An E-Tec might just do a nice job in that capacity, but even in light experimental aircraft where Rotax is king, the liquid cooled two strokes are losing ground to four strokes both air and liquid cooled, many of which are Rotax also. Fuel efficiency and reliability are the reasons, and here is where the weight penalty is FAR more severe than in boats.

 

[Bwalker]

Re: Two Stroke vs Four Stroke?

"But how is it that the E-Tec is so vastly cleaner than anything else? Is it really? The NOx advantage from two strokes must be a result of lower compression ratio or retarded timing, more the former than the latter I suspect"<br />Judge for yourself. http://images.wardsauto.com/files/1004/WEU-April04b.pdf#search='Bombardier%202%20stroke' <br />FWIW I think the decrease nox levels come from the lower exhaust temps of a two stroke. The leaner and hotter you make a four stroke or a diesel the more problems you have with NOX.<br />In regards to the future. It seams to me that BRP has put all their eggs in the two stroke basket. Not because it was easy to do, but because they believe its the best tech available. I admire company like this that has the balls to rise to the occassion and perfect unique technology rather than to roll over and take the easy way out. I fully believe that in the near future one technology will become dominant. If Merc had come out with the E-tec I think the writing would be on the wall since they control a huge portion of the new boat market. With Evinrude I am unsure. They have a lot of negative press to overcome that stems from OMC's bankruptcy and the shortfalls of OMC's ficht debacle. If Yamaha rises to the occasion and brings out something that is comparable(the HPDI isnt)to the E-Tec it would be very easy to see merc do likewise and the industry pendulum to swing back to the two stroke.

 

[TOHATSU GURU]

Re: Two Stroke vs Four Stroke?

Bearcat,<br /><br />I did mean CO. Carbon Monoxide is the baddie, not Carbon Dioxide as I indicated. It has been a long week.

 

[Mike Johnson]

Re: Two Stroke vs Four Stroke?

Ben, You are on the right track, but just a bit off base: The NOx advantage is not due to "lower exhaust temperatures" per sey, but to lower peak combustion temps. It is at high PCT that NOx are formed. Of course, higher PCTs may lead to higher exhaust temps, depending also on some other variables such as volumetric efficency.

 

[Bwalker]

Re: Two Stroke vs Four Stroke?

Your 100%correct UPtraveler.<br />Two cycles have a natural EGR of sorts because it's very rare for them to have a combustion chamber with out some residual exhaust in it.

 

[Mercathode]

Re: Two Stroke vs Four Stroke?

4-strokes seem to be the future of outboards (Merc just spent a 100 mill on their new ones) I prefer the 2-stroke because of lighter weight and the ability to make some serious power. If one goes with the 4-stroke, watch the dealer. Many dealers are selling customers on high dollar services every so many hours (big buck oil changes and the sort).

 

[jurgenscraft]

Re: Two Stroke vs Four Stroke?

This is one of the most interesting threads that I have ever read on this forum and I would personally like to thank all contributors to this particular thread, all I can add is, in my particular case the reason I run a two stroke instead is as follows : Yamaha FT60BET 4 STROKE MOTOR WEIGHS 120 KG (264 lbs.) compared with Yamaha E55CMH 90 KG. (198 lbs.) a difference of 66 lbs pay load on the boat,if you are fishing commercially for a living , a 30 kg (66lb)@ 5 dollars a Kg, difference in catch pays for the fuel for that particular trip,Kind Regards William Wright.

 

[jurgenscraft]

Re: Two Stroke vs Four Stroke?

I wonder if motul oil is available in the USA.? I am sure it is? this is a 100% synthetic two stroke oil and is 85% biodegradable this is a step in the right direction in the battle against water pollution, Kind Regard William Wright

 

[Bwalker]

Re: Two Stroke vs Four Stroke?

"accomplished with a four stroke with fewer gymnastics than a two stroke. "<br />I dont think this is the case at all. Simple carb inducted four strokes will not pass future emmissions regs.In some cases a carb equiped four cycles emmisions is barley better than a twp stroke. <br />Things like fuel injection, no valve over lap(need to increase CC to make same power as a result), catalytic converters, etc. As it is now compare the latest designed four stroke(merc verado) to the latest two stroke(etec) and its plain to see what design is better. Also keep in mind the DI two cycle technology is in its infant stages. It will only get better.

 

[jurgenscraft]

Re: Two Stroke vs Four Stroke?

I would like to quote parts of advert in one of our local fishing magazines called "SKI BOAT"-<br />EVENRUDE E-TEC V6 - 200 225 AND 250 HP.in this advert I read the following E TECH are as fuel efficient as 4 strokes (E- TECH 250 HP 36% more fuel effecient than competitor 4 strokes.<br />E-TECHS are cleaner than the cleanest four strokes, E TECHS are just as quiet as 4 strokes , E TECHS are easier to own and operate (less servicing etc)E-TECHS ARE LIGHTER THAN COMPARABLE 4 STROKES,very important in my case

 

[Bwalker]

Re: Two Stroke vs Four Stroke?

Jurgens, Where in SA are you? I lived in Durban for a month after high school. Loved that town.<br />And yes the new Etecs, are cleaner, more fuel efficant and lighter than the new four strokes.<br />BTW Motul oil is available in the US, but its not very popular. the real problem with two cycles has nothing to do with the oil, bu the fundamental deisgn of the engine that allows a large percentage of the fuel consumed to escape the exhaust port unburnt.

 

[jurgenscraft]

Re: Two Stroke vs Four Stroke?

Hello Ben At the moment I a stationed in Johannesburg ,Gauteng, but I will be moving back down to the big pond,the cape waters are where will I will be fishing for a living again.completing a contract in Jet park Boksburg.<br />Regards William Wright,

 

[kd6nem]

Re: Two Stroke vs Four Stroke?

Ben, <br />The gymnastics I refer to are obvious when raw, primitive two strokes are compared to raw primitive four strokes (carburetors, simple ignition system) as a baseline. The four strokes are cleaner and more fuel efficient to begin with and with each equivalent level of enhancement to each remain that way. The fours are simply not quite as refined yet as the remarkable E-TEC, for some strange reason. (Cars burn pretty darn clean, right?) We know that better has been accomplished in four strokes. The jury remains out as to how much further improvement may or may not be squeezed out of HPDI two strokes. One might be temped to say that E-TEC is a whole new paradigm. I'm still thinking on that; this could be somewhat true although all the pieces brought together were not necessarily original in and of themselves. Maybe E-TEC is almost worthy of a distinction of being something beyond just the next generation of two stroke. Whatever, it is an amazing design. It is a gamble that might just pay off big for OMC.<br /><br />Yes the gymnastics happened for both sides, but the infernal Calif Air Resources Board has set the standard that new two strokes MUST be HPDI where fours may be just fuel injected, based upon their emissions testing. I consider this is a full mile further down the road of emissions gymnastics, personally. As to what the recent comparisons say, this is a matter of the level of attention given each technology by the manufacturers, not anything necessarily inherent in the two stroke vs. four stroke debate. I must give Evinrude a lot of credit here for what they've accomplished.<br /><br />I still maintain that four stroke technology is not fully mature either, ESPECIALLY in outboards. How much further improvement in the E-TEC remains to be seen. If the E-TEC remains as reasonable to operate & maintain as is promised then by all means it will be proven a most excellent motor. Time will tell whether it will remain at the top of the heap or not. That said, we are nearing the limits of efficiency for gasoline power. The next jump in efficieny may be toward diesel (or hopefully biodiesel), given how an open intake causes less drag than a closed or partially closed throttle plate (unless at full open throttle) and how the higher compression and greater BTU availability allow for greater fuel economy. NOx might still be an issue there, however, as might weight.<br /><br />Well, this horse has surely been beat to death, hasn't it? It has been fun & educational, but I don't think I'll have anything further to add until a few years down the road when you guys can tell me "I told you so" or vice versa.

 

[orca]

Re: Two Stroke vs Four Stroke?

Bearcat. Diesel may be the way to go, but not necessarily the traditional diesel as we know it, I believe that Mercury are looking at fueling their Optimax range with diesel. They have released some Optimax motors runnung on JP5 for use by the armad forces. surely biodiesel would be possible, it would be good for the farmers in my area.

 

[tommays]

Re: Two Stroke vs Four Stroke?

well 4 stroke cars still cant cut it with out a CAT !!<br /><br />which is why at some point in the future they will be on sterndrive boats because it is the only way a 4 stroke has been able to meet the requirments on pump gas<br /><br /><br />tommays

 

[Bwalker]

Re: Two Stroke vs Four Stroke?

The etec will run on kerosene/jp-5 also FWIW.<br /> Bearcat, I tend to agree with your train of thought. Except one point and that is the comparative advancment of both types of motors. I think it would be pretty easy to make the argument that the Verado is at least as advanced from a engineering standpoint as the E-tec and maybe more so.<br />Myself, I think BRP has the potential to lead the market with the current e tec design. It would be a slam dunk IMO if it where not for Mercury and to a lesser extent Yamaha controlling many boat builders.

 

[kd6nem]

Re: Two Stroke vs Four Stroke?

Ben,<br />I don't disagree with you regarding the Verado really, just that the E-TEC has made an apparent quantum leap where Verado has a lot of four stroke racing technology more or less behind it; vastly more r&d dollars have gone into four stroke technology by far globally. From my limited perspective Evinrude really pulled off a coup here, apparently with little help from the rest of the world. You are right the Verado is an extremely sophisticated engine, although its performance does not surprise me the way E-TEC does. I expected as much from the four stroke world. Motorcycle racing does this all the time. And you are most probably right as well with the slam dunk statement, assuming (as it sure looks like) that E-TEC is not ultimately plagued by problems as the ill fated FICHT was. Another year or two all speculation will be finished and the history written. <br /><br />Regarding burning diesel in the E-TEC and Optimax- I'd love to see more on this. I'm curious about ultimate efficiency since spark ignited engines and diesel generally do not get along very well. Diesel has more heat for the amount of fuel, and even given the direct injection (a necessity!), computer control of spark & mixture and robust design of the pistons, etc. I still wonder how those motors would hold up. I wonder how much they'd have to be de-tuned to handle it thereby killing some fuel and emissions efficiency? This I must assume is still conventional petro-diesel - biodiesel has an even higher cetane number and isn't likely to ignite well under the wimpy compression of a gasoline designed motor. Plus the biodiesel fuel is more viscous and could be harder for the fuel system to handle without radically increased fuel system pressures- and ultimately wear. Yet biodiesel IMO remains the alternative with the smallest environmental footprint overall and most easy & inexpensive to produce, should we ever decide to become less dependant on foreign entities for our well being.<br /><br />Now the few existing diesel outboards do have a small niche, but are still lead pigs in terms of weight. This could still be improved on a lot, although a true diesel outboard will never equal an E-TEC in the weight department, so far as I can ever see. But they could actually give significantly better fuel economy, despite the excellent performance already being given by the E-TEC magical two stroke. Given enough weight savings in fuel required a diesel outboard might even eventually be the better performer, ultimately. But then we have quite a ways to go before we get there, and a relatively apathetic marketplace which is doing little to encourage such development, unfortunately. At least this is how I see it right now.