2 cylinder vs 3 cylinder fuel consumption

spearmint

New member
Hi guys.

I've just got a very simple question today for all the guru's out there.

After deciding on a small boat, I'm now trying to decide on a motor. I know that the 3 cylinder Yammies are more refined and smoother than the 2 cylinders, but also believe that the 2 cylinders are easier to fix and harder to break generally. Is this correct?

Also can anyone tell me which is definitely lighter on fuel? I'm getting mixed reports?
 
imho, I think you don't have it spot on.
a 3 cylinder engine will give you more torgue, as every 3 turn of the fly wheel you have a combustion taking place, where as with the two cylinder you have every half turn a combustion.

3 cylinders runs much smoother.
any two stroke engine is great, only a one cylinder engine is unbalanced as such and life expectancy is not great.

as long as you have enough oil in the mix, all should go well.

3 cylinder ignition packs are alo more expensive then two cylinder ones.

2 cylinder engines should be lighter on fuel as such, but keeping in mind, when the same hp rating is used,
two cylinder engine would have two bigger pistons then the three cylinder piston engine.

I hope this answers your questions
 
spearmint wrote:
Ok awesome thanks. Why is it relevant that the 2 cylinder has bigger pistons?

nor to go in too deep into the dynamics of engines, but hopefully my explanation says it all.

lets take the Yamaha 40hp engine.
it is a 3 cylinder with a displacement of 693cm 3

please note the 40 hp and 50 hp motors are exactly the same. they normally "choke" the engine so the power output is lower.
by either, main fuel jet supply smaller, carburettor barrel smaller, exhaust port diameter smaller.

so now on a two cylinder engine, you would need two pistons creating the same horsepower as on a 3 cylinder engine.
a single piston on this engine displaces 231cc.

on the 40hp Suzuki engine it is a two cylinder engine with a displacement of
696cm3
and a single piston on this engine displaces 348cc



also see this link: engines compared

http://outboards.findthebest.com/d/h/40
and this

http://www.outboardmotors.com.au/classifieds/show-ad/5860/2013-suzuki-40hp-2-stroke/view-all-outboard-motors-listed/



hope this is all clear
 
the engine mentioned her is quite big.

we can discuss the 30hp engine too.

a interesting aspect here too with the small hp engines are that they too are chocked and many times the same sub assembly is used.

I do know Yamaha 30hp are 3 cylinders too. "don't know if they only come in 3 cylinders, would guess not"

tohatsu on this link uses the same sub assembly.

http://www.tohatsu.co.jp/en/boat/products/mx30sp.html

the 25, 30hp tohatsu are both 2 cylinder engines with a displacement of 429cc

where the Suzuki 30hp engine is also a two cylinder engine and the biggest of the lot with a displacement of 499cc between the two cylinders.

if I ever buy a new set of 2 strokes in the 30hp range, it would be the Suzuki's.
just because of the bigger displacement of the engine.
 

spearmint

New member
Ok thanks again but you have to remember that I know very little about motors so I'm still not sure I've got it.

Just to clarify. I need a 40hp motor and I'm looking for a good all rounder....the 40hp that is lightest on fuel and reliable. So far I'm looking at trying to find a Yamaha 40hp XWL.

With that, I'm guessing that you're saying the bigger cylinders with more displacement, produce more power? If so this thread is still about fuel consumption so I need to find a happy medium and am happy to sacrifice a bit of power for better fuel consumption.

Am I looking at the right motor taking everything into consideration or would you still look at something else?
 

BFC

Senior Member
Spearmint,

Yamaha 3 cylinder 2 stroke motors are super thirsty in their repected HP class compared to others.

in SA they have discontinued the 30 and 40 trips and only really keep the 50/60/75/85's

on the smaller motors the 2cyl yamaha's are real bullet proof products.

I had a pair of 60hp trips and they nearly bankrupted me on fuel for short runs, surf launches OK but for Cape Conditions they were a little too thirsty they were on a 17ft Coastcraft. frequently went fishing with a mate with a 17ft AceCraft with older 55hp Yamaha's and fuel consumption was about 60/70% of the 60's.

the funny thing is that the 85 Yamaha is renowned for being a gas guzzler, yet the 55hp motor not - the 55hp Yamaha being a 2cyl and the 85hp being a trip but both motors use the same CC pistons.

the 60hp trips had a little more grunt out of the blocks than the 55's.

until I had a innings with Mercury 50hp 3cyl 2stroke - at first I did not like them at all because I was taught Mercs are black anchors, They have power galore , very fuel effiecient ( its going to be a toss up between my Suzuki 40 4's and the Mercs on fuel economy if Merc looses it will not be by much)and then price, they are super good value for money, I would also seriously look at the 40hp Suzuki 40 2stroke from a value perspective even a Tohatsu (toaster) 40/50hp 80% of racing rubberducks run on toasters.

Am I confusing you?
 

spearmint

New member
Thanks BFC just to clarify I am looking at getting a used two cylinder not new. I thought i'd narrowed it down. A friend of mine who is a motor mechanic said I cant go wrong with the 2 cylinder 40 Yammie and that it was light so so i'm surprised and more confused to hear that the Suzuki's are lighter...
 

BFC

Senior Member
spearmint wrote:
Thanks BFC just to clarify I am looking at getting a used two cylinder not new. I thought i'd narrowed it down. A friend of mine who is a motor mechanic said I cant go wrong with the 2 cylinder 40 Yammie and that it was light so so i'm surprised and more confused to hear that the Suzuki's are lighter...

if you going to buy a cheapie 2nd hand motor I would stick with Yamaha.

Those 40 2cyl Yamaha's are bulletproof motors , and many of them around that did not work hard.

What hull are you putting it on?
 
spearmint wrote:
Thanks BFC just to clarify I am looking at getting a used two cylinder not new. I thought i'd narrowed it down. A friend of mine who is a motor mechanic said I cant go wrong with the 2 cylinder 40 Yammie and that it was light so so i'm surprised and more confused to hear that the Suzuki's are lighter...

lets confuse you some more.
like I stated the 40 and 50 hp yammies are the same.
so the weight is the same, ie 88 kg.

so if you are going for yammies, why not go for the 50hp.

Suzuki has some stunning 40hp out there, 2 cylinders.

BFC has given you good advise.

the only down fall is. when buying older 2nd hand motors, the yammies spares should be available, but yet expensive.

don't know how spares are available on other manufacturers.
 

spearmint

New member
Sorry I meant light on fuel. Again this is my main concern so 40hp is the max I want to go for my application to keep the fuel consumption down. Spares are a concern but apparently we have an outlet in Durban who brings in tons of clone parts. Obviously I will go original on the important stuff. You must also please bear in mind that this is just going to be my "starter" motor. My intention is to find a cheapish one, give it an overall and use it for a year or two until I can upgrade to ideally two 30's.
 

BFC

Senior Member
spearmint wrote:
Sorry I meant light on fuel. Again this is my main concern so 40hp is the max I want to go for my application to keep the fuel consumption down. Spares are a concern but apparently we have an outlet in Durban who brings in tons of clone parts. Obviously I will go original on the important stuff. You must also please bear in mind that this is just going to be my "starter" motor. My intention is to find a cheapish one, give it an overall and use it for a year or two until I can upgrade to ideally two 30's.

Here is what I would do . I don't think fuel consumption weighs more than purchase price if purchase price is cheap enough. A good second hand Yamaha 2s is going to set you back between R25-30k

I would look at something like this.

http://www.gumtree.co.za/a-boats-jet-skis/amajuba-+-newcastle/angler-kingfish-boat-55hp-yamaha/1001075646130910171203309

That 55hp has never seen salt , it is super clean , its cheap , more than enough power, light enough, heavier on juice than 4 2cyl less than 40 3 cyl.

you get a trailer for free and still recoup R2-3K for your effort and travel to collect, Or use for a year and put the lot together and sell for what you bought it.
 

thika

Sealiner
willem wikkel spies wrote:
imho, I think you don't have it spot on.
a 3 cylinder engine will give you more torgue, as every 3 turn of the fly wheel you have a combustion taking place, where as with the two cylinder you have every half turn a combustion.

3 cylinders runs much smoother.
any two stroke engine is great, only a one cylinder engine is unbalanced as such and life expectancy is not great.

as long as you have enough oil in the mix, all should go well.

3 cylinder ignition packs are alo more expensive then two cylinder ones.

2 cylinder engines should be lighter on fuel as such, but keeping in mind, when the same hp rating is used,
two cylinder engine would have two bigger pistons then the three cylinder piston engine.

I hope this answers your questions


Sure you mean every ONE THIRD turn
 

spearmint

New member
Ok there seems to be some disagreement and since this is still about fuel consumption and I will never be far from shore being a spearo, I think the 40 2 cylinder is still winning. ((s((peed)
 
If you wont be traveling far. In my opinion the difference if fuel consumption between the 2 or 3 cylinder is going to be negligible for you.
 

Limpopoking

Sealiner
Hi Spearmint, my 5c... I had the 440 with a Suz DT40. C-Ski is, IMHO one of the best built boats in SA. The glasswork is just superb. I sold my 440 because I couldn't get 2 motors on the transom. The DT40 was an absolute beaut, very few hours on it, light, economical... I loved it but I hated being on the water with only a single motor.

The 444 has quite a bit more stern buoyancy so 2 motors work fine. If it were me, (and I came quite close to going this route, buying a 444 after my 440) I'd fit 2 x 20/25s.

Sitting on the backline with a single motor, you hear every single misfire of that engine and it resonates deep down into the pit of your stomach.

Sorry to upset the apple cart.
 
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