2 Stroke

[Biggles]

Can anyone tell me what is the point of a 2 stroke engine in the 21st Century.
I can see very few good points for them being continued to be made and lots of bad points. I would like to be convinced otherwise.

Bad points are:-

Relatively worse fuel consumption than 4 Stroke.

Noisy.

Smelly.

Requires expensive special oil.

Good points:-

Lighter than 4 stroke.

Cheaper than 4 stroke.

Said to be easier to repair than 4 stroke but who's going to do that on a warranty motor.

Finally:-

How come no cars have 2 strokes if they have at least a few redeeming features.

Bring it on !!!!!!

[codprawn]

Originally Posted by Biggles

Can anyone tell me what is the point of a 2 stroke engine in the 21st Century.
I can see very few good points for them being continued to be made and lots of bad points. I would like to be convinced otherwise.

Bad points are:-

Relatively worse fuel consumption than 4 Stroke.

Noisy.

Smelly.

Requires expensive special oil.

1. I have yet to be convinced.

2. Only at lower speeds

3. Not at all

4. Only if you believe you MUST use expensive oil.......

As to why they aren't used much in cars they tend to have 3 throttle positions - tickover - 1/2 and full - well mine does anyway!!!

[Stoo]

They have about 1/2 the moving parts of a 4-stroke it seems to me! (And this strikes me as a good thing...!

[chris123]

The big selling points of 2 stroke engines are power to weight ratio, throttle response and simplicity. This is why (going back a few years) a Yamaha 350cc 2 stroke bike could match a 600cc+ 4 stroke bike for performance.

As Codprawn has said, the downside is the powerband - maybe not so relevant on an outboard, but on a twisty road on a 2 stroke bike you will be rowing up and down the gearbox to keep it in the powerband where a 4 stroke can just roll on and off the throttle. Various companies have come up with ways to improve this (eg Yamaha's power valve that varies the exhaust timing) but you still end up with a very peaky motor.

This is one of the reasons why 2 stroke engines aren't used in cars (IIRC some very early / east european cars did use 2 stroke engines). The other issues are that 2 stroke engines wouldn't (AFAIK) pass modern emissions regs, and also (going from motorcycles) have a much shorter life expectancy than an equivalent power 4 stroke.

Cheers

Chris

[Roy Smith]

If there is less moving parts then why dont they last longer,
I am trying to convince myself that 2 stroke (Etec) are the way to go,
Big problem i am having is that the people who do have major issue,s
with there engines don't speak up and that is 2 stroke and 4 stroke owners.
I have said before if 2 Stroke is the way to go why have Suzuki Yamaha Honda
all invested heavily in four stroke.

[Bigmuz7]

Originally Posted by Roy Smith

I have said before if 2 Stroke is the way to go why have Suzuki Yamaha Honda
all invested heavily in four stroke.

Emissions quite simply. No one is going to be convinced about a motor throwing oil out the exhaust all the time.

I always saw Mercury Optimax technology as being a good compromise, it is still a two stroke, but it doesnt pop, fail to start hot, or die from rest when you try to pull up a skier. The fewer moving parts issue is a good point, but with fourstrokes, valve gear is so reliable that the two stroke advantage in moving parts is much less so, save for the extra weight, that this stuff adds to the engine.

One things for sure, some fours need to be engineered lighter imho

[matt h]

my 115 opti is far more economical the the same size 4 stroke, extremely happy with it, and i know as i have done the figures!!

[chris123]

Originally Posted by Roy Smith

If there is less moving parts then why dont they last longer,
I am trying to convince myself that 2 stroke (Etec) are the way to go,
Big problem i am having is that the people who do have major issue,s
with there engines don't speak up and that is 2 stroke and 4 stroke owners.
I have said before if 2 Stroke is the way to go why have Suzuki Yamaha Honda
all invested heavily in four stroke.

I would assume that one of the 2 stroke reliability issues is lubrication - with the bottom end of a traditional two stroke being lubricated by the petrol-oil mix, it is never going to be as well lubed as a 4 stroke - certainly big end / small end failure is 'relatively' common on two stroke bike engines.

Honda, Suzuki and Yamaha have always had R&D effort into both 2 stroke and 4 stroke engines, primarily through bikes but also through cars. I would suspect that their 4 stroke outboard options share a lot of commonality with their bike and car engines - for example the Honda BF90 outboard is listed as using a derivative of the Jazz car engine, so 4 stroke is probably a cheaper development option than 2 stroke. With the demise of the 2 stroke bike, the outboard market is probably too limited to be worth major R&D work.

Evinrude (AFAIK) only have 2 stroke experience, so for them improving the two stroke is presumably a cheaper option (and a better marketing strategy) than trying to develop their own 4 stroke.

Of course, all manufacturers will tell you that their chosen development route is to provide you with the best possible product, but the root cause is often cost saving and minimising time to market.

Cheers

Chris

[iainmartins]

I reckon di 2 strokes are better than most 4 strokes for a rib. My optimax gives better fuel economy than similar 4 stroke (if you dont thrash it), throttle response is quicker, torque shouldn't be an issue (envinrude e-tec claim they provide more than equivelant yam). They are slightly lighter and the performance figures that i have seen are always better. Servicing is less critical.
The only down sides are emissions, 2 stroke oil, louder (but they make a nice noise) not as good at trolling speeds (when do I ever do that!)

[BogMonster]

Originally Posted by Roy Smith

I have said before if 2 Stroke is the way to go why have Suzuki Yamaha Honda
all invested heavily in four stroke.

I read somewhere (probably RIB Intl) that it was basically down to marketing and future emissions - many people "have to have a four stroke" because they are "the thing to have" and also the designs are apparently easier to modify for expected tighter emissions regs in the future.

[codprawn]

It is a good point about development costs - the majority of 4 stroke outboards have other applications. The new yam 350 is based on a Ford V8 car engine.

As to oil going into the water a lot depends on the oil and the ratio - remember eventually a 4 stroke's oil will also end up back in the environment - especially if someone just chucks it away.

[jyasaki]

Originally Posted by codprawn

It is a good point about development costs - the majority of 4 stroke outboards have other applications. The new yam 350 is based on a Ford V8 car engine.

I think there's been a lot more research and testing on 4-strokes, due primarily to the larger market share they enjoy.

A few years back, there was some experimenting done with a 2-stroke engine that used sumped lubricating oil and ran on pure gas. Not sure why that didn't go further than it apparently did.

As to oil going into the water a lot depends on the oil and the ratio - remember eventually a 4 stroke's oil will also end up back in the environment - especially if someone just chucks it away.

That's sort of like saying that a wood bridge is a better alternative to steel because eventually someone will toss the steel on the side of the highway. If you assume the oil is going to be recycled (and ideally, many times), well, yes, it will still end up in the environment, but only after many, many cycles of uses. A 2-stroke engines oil gets into the environment after a single use.

Speaking of which, I think my oil storage bucket is full, and today would be a good day to take it to the recyclers for emptying.

jky

[codprawn]

What if it's castor oil??? Great in 2 strokes!!!

[Bulligmore]

I think the fuel consumption of new engines, 4 and 2 stroke are the same. Oil not that important as they both use it in different ways. But power to weight is important with a small RIB. If you are using your RIB in rough water I think the 2 stroke power band has the edge. If I was buying a small Rib it would have a 2 stroke on the back and a very big RIB inboard deisel.

[Daveboy 71]

Just got back from a dive trip to the south coast during which I had a very interesting conversation with the owner of the dive centre. Basically he was very unhappy after replacing his old optimax with a V-6 Yamaha 4-stroke of comparable power (225 HP). To his surprise the latter could no longer get the rib onto the plane with a full load of divers which is basically a disaster if trying to run a diving rib service.
The latest DI technology has taken 2-strokes to the next level. They still have huge amounts of torque to draw upon whilst achieving better economy and improved emissions relative to the old 2-stroke technology. I think the Evinrude Etec has now been granted permission to operate on the Swiss lakes and is the first such 2-stroke technology to achieve this landmark. Basically the Etec is as good as a 4-stroke re. fuel economy, noise, emissions whilst having much more torque!!! The questions is why pay more for a 4-stroke that is less powerful (torque), heavier and needs servicing very 100 hours?

Dave

[Roy Smith]

I think there is a pattern emerging, The Etec/ 2 stroke folk love there Etec the Four stroke people love there 4 strokes.
We all have tales to tell about the fantastic virtues of our particular engines
If the man with the dive rib changed his prop to suite the weight he is carrying it might help.On Saturday i spoke with a man who only supplies Etec,s he has had lots of problems, but then so have Yamaha with there 300 HPDI so where dose this leave us, Seams that most of the Boating done is in shore ,short bursts of power for a few miles so its not really relevant. Looking at our cruise on tues / Weds we average 38 knts to Guernsey but this worked out at about 3 to 4 miles per gallon, WOW thats some carbon foot print,some thing i have wanted to ask about is exhaust emission's into the water on cars we have catalyst converter Boat engines ?

[codprawn]

Water filtration is incredible - they are now looking at squirting it into lorry exhaust pipes.

The sea is a very big place and a little extra HNO3 will soon break down. The CO2 from the exhaust will also be absobed to a certain extent although not sure how much.

[Bigmuz7]

Originally Posted by Roy Smith

I think there is a pattern emerging, The Etec/ 2 stroke folk love there Etec the Four stroke people love there 4 strokes.

Not quite.. I think optimax is making some headway in this thread.. and thats from a fourstroke owner (me) who used to have an optimax ! Verado is good, but its heavy.. but jeez it has instant power

[fast fred]

Ok then, the TWO Stroke. what is it,it IS twice the POWER at HALF THE WEIGHT
OF A FOUR Stroke.thats what it is, this was true when invented and is Still true TODAY.

ya your savin gas, goin half as fast, lugin twice the weight.

[ribit]

I to tend to think a bit like fast fred it's a no brainer 2stroke for me all the way, my problem is some friends are technicians for expensive well known car makes all day long they spend time fixing ever more complex problems, do you realy want to hang this kind of problem on your boat, although as somebody pointed out...who cares it will be new under warranty and when it gets a few miles under it's belt I will get shot off it...maybe but at that point to me it's worth peanuts for it's now just one complex 4 stroke with a worn cam belt waiting to let you down or worse go bang