Yamaha 9.9 2 or 4 Stroke

Fire99 said:
Just bear in mind that yes you are burning 1:50 - 1:100 amounts of 2-stroke but each year you aren't draining a sump of oil and dumping it along with an oil filter that has to be disposed of.
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Good point......did'nt consider buying a new oil filter & that routine maintenance but I expect you could stretch it out for more than a season depending on usage.......still think the efficiency of not blowing additional oil out the exhaust & the benefits to the environment are attractive.It's a neater engineering solution:cool:
 
Dockhead said:
Not a fair comparison at all. Dirt bike two-stroke engines are tuned to get maximum power at screeching revs, and have expansion pipes and so forth. They are like F1 engines which put out huge power in a narrow rev range, and nothing above or below that. So of course your mildly tuned Tiger Cub putt-putt bike would outpull them lugging up a slope. That has nothing to do with whether it was a four-stroke. It has everything to do with the difference in the way they were tuned.

I can give you a counterexample which is closer to the marine situation -- snowmobiles. My two-cylinder Rotax 600cc two-stroke snowmobile engine produces 115 horsepower at 8,000 RPM and weighs only 28 kilos (!) (without exhaust and fuel systems, but still).

To get a similar amount of horsepower out of a four-stroke, Yamaha require three cylinders and 973cc, running at almost 9,000 RPM, and weighing more than double. The smaller Rotax two-stroke has a broader power band, and about 20% more torque than the Yamaha despite smaller capacity..

I wasn't able to find torque specs for those two outboards, but two-stroke engines have more torque than similary tuned four-strokes. That is because you get double the number of power strokes out of a two-stroke.
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Why are the majority of yacht auxiliaries diesel then?
I can't see that you can compare competition two strokes & snow mobiles with little loading & light weight against the sort of power needed to drive a quite heavy displacement yacht through the waves.
A good plodder with a fair amount of power is more what you want it seems to me......economy & efficiency.
 
kristifercolumnbus said:
Good point......did'nt consider buying a new oil filter & that routine maintenance but I expect you could stretch it out for more than a season depending on usage.......still think the efficiency of not blowing additional oil out the exhaust & the benefits to the environment are attractive.It's a neater engineering solution:cool:
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Fair comment but purely personally, 4-Strokes have so many more parts that all have to be manufacturered and steel that has to be 'extracted' and processed. It's all part of the equation.

Also the 2-strokes that you speak of (the nice slightly smelly ones) were designed for purpose. Cheap and simple build with very good power output and light weight too. All factors which are great for the marine market.
They were never designed to be the last word in CO2 efficiency.

Now look at modern direct injection 2-strokes like the Evinrude E-TEC. No smells, no fumes and super efficient. Too efficient in my book with having to be more complex to keep the EU emmissions folk happy but, personally speaking, it's a shame more people don't go down this route so the technology could become cheaper and a sub-25hp version could exist.

I still don't buy the 'dirty' 2-stroke thing. IMO pollution etc needs to be looked at as a whole, (We all live on one earth) without the political and commmercial spin put on it. In the big picture of things, banning new small 2-strokes from the EU has no real environmental benefit and just makes more expense and hassle for boat owners.
 
Dockhead said:
I have a bit of a sentimental attachment to two-strokes, I will admit. I've been a motorhead almost from birth, and I love all kinds of internal combustion engines. I bought my first Porsche in 1982 -- a 2.2 liter 911S, which had one of the all time great motors I've ever owned. I've had various Porsches and BMW's since then; most recently I've had the 4.4 liter BMW V8 engine in my last couple of vehicles, a truly great power plant. I've had motorbikes of various kinds (no two-strokes, to my regret), including a four-cylinder Honda 750 which was a great motor in its time. I love diesel engines; I love the way they sound and the way they work. I even love lawnmower engines. I love the three-cylinder Yanmar diesel in my Kohler generator. I have loved all of the two-stroke outboards I've owned over the years. And I love the Mercury 40 horsepower four-stroke outboard on our lake boat.

But I have an entirely special love for the 600cc two-stroke engine in my snowmobile. This is a vehicle which weighs about 400 pounds but is moved by 115 horsepower. It is the closest thing to flying you can do without wings. It can ascend an almost vertical slope (one which you couldn't ski down) on a virtually ballistic trajectory using not traction, but the thrust produced by the jet of snow propelled behind the track. The Rotax motor is amazing. It is like the pure idea of power directly translated, somehow, into reality. The response to throttle is so intense, that the response time is undetectable. It seems not even like a response to moving your thumb, but just thinking about moving your thumb creates an explosion of power and you are already in motion, without noticing that you have even accelerated. It is the most amazing thing; and this kind of responsiveness is unique to two-strokes. If you have room to let the sled run, five or six seconds of full throttle feels like, not like the way a motor vehicle runs, but like the first-stage burn of a rocket motor. And yet the thing will potter around happily all day long at 5 mph picking your way through rough terrain, it starts in half a revolution with just a little flick of the starting cord, and has never given the slightest trouble in six years of hard use amounting to a couple of thousand hours. I didn't even change the plugs this year; just didn't get around to it. And that's just about the only maintenance you do. This is probably my all time favorite engine ever, and it has definitely prejudiced me in favour of two-strokes.
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Yeah well I have had plenty of experience building & rebuilding old two strokes & the romance wears off when the sods are old & keep braking down just like any machine.
I still like engineering & am a perfectionist but all this stuff costs money & to me now the environment & Nature are paramount that's why I go sailing.Somehow I just cannot reconcile myself to an engine that just blows out oil as an ultimate Engineering solution.....it's against the beauty & laws of nature.
That Rotax engine sounds interesting but then so did the wankle engine,I wonder whatever happened to that?:)
 
Fire99 said:
Fair comment but purely personally, 4-Strokes have so many more parts that all have to be manufacturered and steel that has to be 'extracted' and processed. It's all part of the equation.

Also the 2-strokes that you speak of (the nice slightly smelly ones) were designed for purpose. Cheap and simple build with very good power output and light weight too. All factors which are great for the marine market.
They were never designed to be the last word in CO2 efficiency.

Now look at modern direct injection 2-strokes like the Evinrude E-TEC. No smells, no fumes and super efficient. Too efficient in my book with having to be more complex to keep the EU emmissions folk happy but, personally speaking, it's a shame more people don't go down this route so the technology could become cheaper and a sub-25hp version could exist.

I still don't buy the 'dirty' 2-stroke thing. IMO pollution etc needs to be looked at as a whole, (We all live on one earth) without the political and commmercial spin put on it. In the big picture of things, banning new small 2-strokes from the EU has no real environmental benefit and just makes more expense and hassle for boat owners.
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Maybe the answer would be to recycle or cleanse the exhaust system,anyway I love two strokes for their simplicity....but I love nature more.
 
kristifercolumnbus said:
Maybe the answer would be to recycle or cleanse the exhaust system,anyway I love two strokes for their simplicity....but I love nature more.
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I hate to bang on about it. but Evinrude E-TEC 2-Stroke. As 'green' as any..

Nature? Well sadly i'm going to disagree with you till the ends of time on this one. Based on total environmental impact from build to scrap, i'd wager the EU banning new small 2-strokes has had zero beneficial impact on the environment.

Also, if i'm gonna be picky, by your own admission of 'stretching out' the service intervals of the 4-stroke, will have no positive benefit on the clean running of the engine.

It all counts.
 
kristifercolumnbus said:
Yeah it was said to out accelerate other cars & be smoother & from what was explained to me all those years ago it looked wonderfully simple.Did'nt Honda bring out a large touring bike?
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Was that not the RX-7? The RX-8 is fairly middle of the road and even new doesn't do the best MPG and for a new car doesn't have the best oil consumption.

I can't see you driving one of those. :D
 
kristifercolumnbus said:
Yeah well I have had plenty of experience building & rebuilding old two strokes & the romance wears off when the sods are old & keep braking down just like any machine.
I still like engineering & am a perfectionist but all this stuff costs money & to me now the environment & Nature are paramount that's why I go sailing.Somehow I just cannot reconcile myself to an engine that just blows out oil as an ultimate Engineering solution.....it's against the beauty & laws of nature.
That Rotax engine sounds interesting but then so did the wankle engine,I wonder whatever happened to that?:)
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Well, sure, but that's not specific to two-strokes. Any worn-out engine becomes less romantic, until you rebuild it of course . . . .

The Rotax doesn't blow oil out; it has metred oil injection (you don't mix oil with the petrol) and semi-direct fuel injection, so it's very economical and doesn't smoke.

Of all means of propulsion, however, you are right -- sailing takes the cake, however you look at it . . . .

That's why I don't have a mobo . . .
 
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kristifercolumnbus said:
Why are the majority of yacht auxiliaries diesel then?
I can't see that you can compare competition two strokes & snow mobiles with little loading & light weight against the sort of power needed to drive a quite heavy displacement yacht through the waves.
A good plodder with a fair amount of power is more what you want it seems to me......economy & efficiency.
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Well, all large internal combustion ship engines are two strokes . . . and most railway engine diesels are two strokes.

It used to be possible to get a Detroit Diesel two-stroke yacht engine (there's even a chapter on it in the Calder book). I wish they made a modern version of it; I'd love to have one in my boat.

Two strokes make very good "plodders" if they're tuned for it, for the simple reason that you have more power strokes.
 
davidej said:
How come you can get a new 2s in Lisbon when we are denied them?

I thought the banning of the sale of 2Ss was europe wide.

It this another example of the british enforceing regulations which the rest of europe ignore?

Sorry - rant over!
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It's one left over from stock
 
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