Yamaha 9.9 2 or 4 Stroke

Thanks for that info. I am more and more for te 4-stroke

The old motor was not a high thrust but it had a mickey mouse ears high thrust prop on it.That's what I will go for now again as it was easy enough power.

I agree, normally always sails over motor whenever possible, and maybe I should have tried with my sails in Germany, but (as well as being stupid enough to leave the Harbour in the first place!) we were heeling to 30 degrees with the stack pack and mast alone, and with the motor we could sneak along in the lee of the shore avoiding the worst of the waves, then the entrance to the harbour would have been a beat through a mile long 15m wide channel with expanses of submerged sand/mud banks either side. In Oeiras there was no wind!
 
kristifercolumnbus said:
Not true.Four strokes have more low down power suitable for pushing heavy yachts.
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I should point you to the Mobo forum right now where there is a 2S vs 4S debate. Everyone seems to agree that 2S has the most torque. Evinrude even do a nice little video against a Yamaha to prove the point.

The only 4S that compare are supercharged ie. Verados.

PS. I think the point you are making is about propeller pitch more than torque
 
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rb_stretch said:
I should point you to the Mobo forum right now where there is a 2S vs 4S debate. Everyone seems to agree that 2S has the most torque. Evinrude even do a nice little video against a Yamaha to prove the point.

The only 4S that compare are supercharged ie. Verados.

PS. I think the point you are making is about propeller pitch more than torque
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Many years ago I used to be mad keel on motor bikes particularly trials bikes & I had several different makes & extensive experience doing them up.Bultaco's Ossa's Yamaha's etc you name it & then I got a Triumph Tiger cub that I did up as a trials bike.That bike used to pull my firefly dinghy up & steep slope no trouble at all practical on tick over & I am absolutely certain that none of the two strokes could have matched it unless I revved the guts out of them......absolutely no competition.
Two strokes might well have acceleration & be nippier but they certainly don't have more power.
 
Inselaffe said:
Thanks for that info. I am more and more for te 4-stroke

The old motor was not a high thrust but it had a mickey mouse ears high thrust prop on it.That's what I will go for now again as it was easy enough power.

I agree, normally always sails over motor whenever possible, and maybe I should have tried with my sails in Germany, but (as well as being stupid enough to leave the Harbour in the first place!) we were heeling to 30 degrees with the stack pack and mast alone, and with the motor we could sneak along in the lee of the shore avoiding the worst of the waves, then the entrance to the harbour would have been a beat through a mile long 15m wide channel with expanses of submerged sand/mud banks either side. In Oeiras there was no wind!
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I think your right.If I had the money I would probably buy a 8hp sail drive 4 stroke to replace my 9.9 hp Mercury.
I think the cost of all that two stroke oil would swing it & it's no way to treat the environment.
 
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kristifercolumnbus said:
I think the cost of all that two stroke oil would swing it & it's no way to treat the environment.
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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.
 
kristifercolumnbus said:
Many years ago I used to be mad keel on motor bikes particularly trials bikes & I had several different makes & extensive experience doing them up.Bultaco's Ossa's Yamaha's etc you name it & then I got a Triumph Tiger cub that I did up as a trials bike.That bike used to pull my firefly dinghy up & steep slope no trouble at all practical on tick over & I am absolutely certain that none of the two strokes could have matched it unless I revved the guts out of them......absolutely no competition.
Two strokes might well have acceleration & be nippier but they certainly don't have more power.
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Exactly, that's nobody makes a 2 stroke car...or lorry...or bus.
 
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kristifercolumnbus said:
Many years ago I used to be mad keel on motor bikes particularly trials bikes & I had several different makes & extensive experience doing them up.Bultaco's Ossa's Yamaha's etc you name it & then I got a Triumph Tiger cub that I did up as a trials bike.That bike used to pull my firefly dinghy up & steep slope no trouble at all practical on tick over & I am absolutely certain that none of the two strokes could have matched it unless I revved the guts out of them......absolutely no competition.
Two strokes might well have acceleration & be nippier but they certainly don't have more power.
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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.
 
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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Yep! :) Gotta agree.

One issue 2-strokes have never suffered from is power to weight / capacity.
 
Kochi said:
Exactly, that's nobody makes a 2 stroke car...or lorry...or bus.
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Nonsense.

A large percentage of the worlds lorries and busses, and all very large low-speed internal combustion ship engines, are two-strokes. Most railway diesel engines are two strokes. The larger the diesel engine, the more likely it is to be a two-stroke.

I guess you've never heard of the Detroit Diesel two-stroke engines, which amounted to nearly half the market for lorries and busses at one time, and are still produced. Commer also made two-strokes for lorries and busses, and the Junkers Jumo aircraft engine was a two-stroke diesel.

See:

http://www.dieselpowermag.com/news/0709dp_detroit_diesel_engine_history/index.html

http://www.marinediesels.info/Basics/the_2_stroke_engine_explanation.htm

http://www.dieselduck.ca/machine/01 prime movers/diesel_engine/diesel_engine.01.htm


Two-stroke car engines are not currently made because of fuel economy and emissions reasons, and for no other reason. Two-stroke petrol engines are inherently less fuel efficient because some fuel-air mixture is wasted out the exhaust port.

But this drawback is being corrected with direct injection. The new Evinrude direct-injected two-stroke outboards and Rotax direct-injected snowmobile engines are now about equal to good four-strokes in fuel economy and not too far off in emissions, while preserving the two-stroke advantages in power, lightness, torque, simplicity.

New two-stroke engines are being developed for cars, both diesels and spark-ignition engines. Lotus have been working hard on a flex-fuel direct-injected two-stroke engine they call Omnivore; they say it is the future of car engines.

See:

http://www.autoblog.com/2008/08/12/lotus-developing-efficient-two-stroke-omnivore-engine/

http://www.greencarcongress.com/2005/05/fev_developing_.html
 
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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Dockhead is still on the money and right.

My old boss's boat had a big ol 2-stroke Diesel Tank engine in her and believe me that is all about low-down power.

It's also worth considering that AFIK it is only the EU that has outlawed the conventional 2-stroke (Evinrude's E-Tec advanced 2-stroke lives on!) and if you look beyond politics and look at the Total environmental cost of 'old-tech' 2-strokes, including their usage, then it's just political nonsense.

For marine use, after owning a very modern 4-stroke O/B for a year, 2-stroke is still far better in my book than 4.
 
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!
 
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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What 2-stroke motor? If it's a small (sub 25hp) then i'm surprised. If it's 25hp above then Evinrude's E-TEC 2-strokes are perfectly legal in Europe.
 
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!
Click to expand...

What 2-stroke motor? If it's a small (sub 25hp) then i'm surprised. If it's 25hp above then Evinrude's E-TEC 2-strokes are perfectly legal in Europe.
 
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!
Click to expand...

What 2-stroke motor? If it's a small (sub 25hp) then i'm surprised. If it's 25hp above then Evinrude's E-TEC 2-strokes are perfectly legal in Europe.
 
davidej said:
PS

Dockhead - you must get out more. loving all these engines is really not good for you!
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LOL!

A true motor head would not have made that comment, but nevertheless you're right. Having to sit behind a desk addles the brain. Can't wait to get out on the water.
 
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I have put down a deposit on the 4 stroke F9.9F,

One other thing is that Yamaha have discontinued the 9.9 2-stroke

now to try to find the right Dual thrust prop...

Thanks for all the input
 
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