Whats the difference bettween the 2 stroke and the 4 stroke?

[EmicMalta]

Maybe this is a stupid question but always talking with people and say "buy a 4 stroke" and then when you read reviews everyone says that are not of best performance.
Im thinking to get a new engine. A friend of mine with a boat that I m going to get had installed an 20Hp Mariner 4 stroke and he s not happy so much with it. For his boat he needs more power so he s going for a 30Hp. Same boats are operated with yamaha 15Hp 2 stroke and perform very well. Th boat is 14ft

People say that 20hp compared with 30hp, one has to calculate that 20kg more weight. For me that i m going to use it even for diving cant see it too much weight cos thats  just the weight belts. Does these engins react so bad with that minimum of weight?

[baghira]

Cost compared I am very sceptic today.

A service for my engine costed 300euro (normal service).

[Jonathan]

I don't know whether it's due to weight but our club has a 13ft boat on which an 2 stroke 8hp outboard was installed, and this was replaced by a 9.9hp 4 stroke outboard of the same brand. The boat was much faster with the smaller hp 2 stroke outboard than with the new larger hp 4 stroke.

[SEAFOX]

I have 2 x 115 hp Yamaha 4 stroke engines (not new) on my boat which I have utilized only this year. Despite agreeing that between a 2 stroke and a 4 stroke there is a difference in the power generation I cannot complain about my motors for many reasons. They are practically emission free, silent, smooth and can run without any problem at low revs which when trolling is really important,winterizing is a simple process. No "oil clogging" in certain systems, carb, fuel filter etc. that one experiences on 2 strokes. Having stated the above we have since my childhood always had 2 strokes on our boats and they performed really well. Bottom line...."like with like", a 2 stroke is stronger, lighter than a 4 stroke and probably more economic to run.
You can leave a 4 stroke idle for several months without any problem but you have to fire up a 2 stroke periodically. Yes, as baghira correctly states 4 stroke servicing is rather expensive. Eventually 2 strokes would not be commercially available anymore cos of this "environment thing". In fact in the US one can note very large boats, having 2 or 3 huge outboards, none are hooked up with 2 stroke motors and nobody there ever mentions these engines.
Baghira - can you let me know on my email address who did your servicing and I will tell you the guy that I found quite "reasonable and qualified".- Tks

[taxxara]

for the same cc, a 2stroke is 1.6 times as powerful as a 4stroke(in general).But then a 4sroke is more efficient and much more reliable but then its heavier. so for a boat using 10hp 2 stroke, you would probably need a 15hp 4stroke for the same performance. but personally i would always go for the 4stroke.. much much more quiet and reliable.. unless its only speed you are after.

[ganni]

are you sure that 4strokes are more reliable?? i tought it was the other way round due to less moving parts

[skip]

Colin, don't forget the 2strokes that the guys are now referring to are all direct injection computer controlled engines with better emissions than some 4 strokes! Engines like the ETEC, Optimax etc.

There are a lot more moving parts on a 4 stroke engine and they don't generate power as often as a 2 stroke on each stroke of the piston, they have camshafts with timing belts that require adjustment etc hence the higher service costs and need for a good mechanic.

On smaller boats you need far more power from a 4 stroke in terms of hp than you do compared to a 2 stroke hence the differences mentioned above. Thing is the direct injection 2 strokes in the smaller hp ranges are just as heavy as the 4 strokes or maybe only a little bit lighter.....

Reliability issues are mentioned above, if you look online you will find that historically 2 strokes are mechanically reliable due to their simpler design and operation....what used to let them down was carburettor related issues. As you can no longer buy a carb'd 2 stroke, what remains to be seen is how well the ETECs and Opti's hold out over time.

From my experience this summer on the RLR RIB which had twin 250 ETECs I would say they were noiser when running both at idle and cruise but very smooth and impressive.

Emic if this boat is of an older design remember that they were not designed for the heavy modern engines so aside from the transom getting stressed even the hull performance might not be as good with such a heavier engine.

[redhead]

the e-techs have better or equal emmission to any 4 stroke outboard. Regarding power keep in mind that mercury had to fit a super charger on it's new verado to give it the power output of a competition direct injection 2 stroke. Are you sure that a super charged 4 stroke is more relaiable than a 2 stroke? I may not agree at all. It has got at least 30% more parts in it that can go wrong. If for whatever reson you don't want an e-tech buy an optimax which is also a two stroke. The 4 stroke outboards went into the  market in the late 90s as an easy fix to the emmision problems. Once the emmission problems are fixed  on a 2 stroke there are only advantages .... 

[SEAFOX]

I agree to a certain extent with all you guys above, Skip, redhead,taxxara and gianni. On my post I expressed just the simple pros & cons and purposely did not go into any technical details. Many of these can be found on "forums" found on the internet regarding engine comparison. Obviously it's not an easy choice when coming to decide what type of outboard to purchase, but personally if I had to buy an engine for a smaller boat needing say a 20hp or 30hp motor I would definitely go for a 2 stroke. In fact I do have a 9.8 LS Tohatsu for my 12 ft boat and it's its a joy to use.

[taxxara]

yes, the 4sroke has more moving parts but the technology is very well developed and so it is reliable. its expensive to service because you go to expensive garages. if you know a thing or 2, you would be amazed how easy it is to do this yourself. and if you know a thing or 2 you can also take care of a 2stroke engine. im not an expert but i know a thing or 2 and i would go for a 2stroke engine only if its speed im after. of course this is my personal opinion biased towards 4stroke because of the old 2strokes to be honest. just dont forget 2strokes are not as efficient(for sure cos of how the engine works) and there is the extra cost of oil...

[baghira]

Dont forget taxxara that 4 stroke engines have engine oil which costs a lot and has to be replaced every 100 hours which comes equivalent to 2 stroke oil consumption.

[EmicMalta]

Dont forget taxxara that 4 stroke engines have engine oil which costs a lot and has to be replaced every 100 hours which comes equivalent to 2 stroke oil consumption.

good point that I had never heard about it

[SEAFOX]

How correct you are baghira, - I got, or found, a half full can of Yamaha engine oil with my boat when it was shipped from the USA and the marked price for 5 liters is US$15.00 The agent here sells exactly the same can of oil for Euro40.00! Not sure about this price but that is what I was recently told by my mechanic. If this is the case then it's simply "daylight robbery". Everything in our country is double or three times the cost found in the USA or even in Europe.....and we "crazy guys" who practice this passionate hobby have no choice but to pay stiff prices.

[busumark]

4 litres of good quality 2-stroke oil costs 30 euro so it is not cheap. and you can use it before 100 hours. it depends how much your motor burns fuel