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Old 11 August 2007, 21:27   #1
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2 Stroke

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 !!!!!!
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Old 11 August 2007, 23:05   #2
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Quote:
Originally Posted by Biggles View Post
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!!!
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Old 12 August 2007, 00:42   #3
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They have about 1/2 the moving parts of a 4-stroke it seems to me! (And this strikes me as a good thing...!
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Old 12 August 2007, 05:30   #4
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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
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Old 12 August 2007, 08:48   #5
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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.
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Old 12 August 2007, 09:03   #6
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Originally Posted by Roy Smith View Post
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
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Old 12 August 2007, 09:24   #7
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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!!
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Old 12 August 2007, 09:40   #8
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Quote:
Originally Posted by Roy Smith View Post
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
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Old 12 August 2007, 10:25   #9
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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!)
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Old 12 August 2007, 13:35   #10
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Quote:
Originally Posted by Roy Smith View Post
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.
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