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Old 01 June 2011, 14:47   #1
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Consumption old style 2 stroke vs 4 stroke/HPDI

Would be interested in some very rough figures for fuel consumption for an old style 2 stroke (Tohatsu 120hp) vs a typical, similar sized 4 stroke or "high tech" (i.e Optimax/ETEC) 2 stroke?

Interested in approx how much more fuel the 2 stroke would take compared with the more modern engines. Any ball park figures/percentages would be really helpful.

Trying to work out whether the money saved on a RIb with a low tech engine would soon be burned away in fuel costs, or whether the purchase saving would buy several seasons worth of fuel.

Thanks,

Gerry
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Old 01 June 2011, 16:07   #2
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Did lots of work on this a while back at Barrus.

4 strokes and Optimax on average 33%-40% better on fuel than a conventional 2 stroke engine. But only downside with the Opti/Etec is you still need to put 2 stroke oil in which is worth factoring in!
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Old 01 June 2011, 16:15   #3
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Quote:
Originally Posted by Gerry View Post
(Tohatsu 120hp)
Although the max they make is 115, if it is a Tohatshu TLDI then it counts as "new tech" etec/opti.

Fuel wise - big engines burn lots of fuel, simple as
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Old 01 June 2011, 16:16   #4
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Quote:
Originally Posted by Turbodiesel View Post
Did lots of work on this a while back at Barrus.

4 strokes and Optimax on average 33%-40% better on fuel than a conventional 2 stroke engine. But only downside with the Opti/Etec is you still need to put 2 stroke oil in which is worth factoring in!
Don't forget the costs of servicing
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Old 01 June 2011, 16:22   #5
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Are 2 strokes significantly cheaper to service than 4 strokes? I've paid between 250 and 350 (needed some extra stuff done) for the last two services on my Suzuki DF60 (i.e. 4 stroke), which strikes me as being a bit expensive!
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Don't forget the costs of servicing
Servicing video
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Old 01 June 2011, 16:22   #6
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Quote:
Originally Posted by Turbodiesel View Post
Did lots of work on this a while back at Barrus.

4 strokes and Optimax on average 33%-40% better on fuel than a conventional 2 stroke engine. But only downside with the Opti/Etec is you still need to put 2 stroke oil in which is worth factoring in!
Thanks - useful figures.

To clarify for the other poster, it's an old Tohatsu, not a TLDI.

Are 2 strokes significantly cheaper to service than 4 strokes? I've paid between 250 and 350 (needed some extra stuff done) for the last two services on my Suzuki DF60 (i.e. 4 stroke), which strikes me as being a bit expensive!

Gerry
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Old 01 June 2011, 16:27   #7
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To add to my last:

Costs video
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Old 01 June 2011, 16:37   #8
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I have an magazine(unfortunately in Finnish) with an overview of most common 2 strokes (over here) with some test figures. Tohatsu 120 hp consumption figures:
WOT=52,2 l/h, -500 rpm 42,0 l/h, -1000 rpm 35,2 l/h. Tohatsu was the thirstiest in this test, Yamaha 115 most economical, especially in the -1000 rpm(from WOT), almost 8 litres /h less than the Tohatsu.

Generally speaking, at WOT speed there is not much difference with modern engines and a good 2 stroke(as an example yam 90 AETO compared to modern 90 hp engines). But when You decrease the rpm, difference start to occur.
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Old 01 June 2011, 16:56   #9
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Quote:
Originally Posted by Turbodiesel View Post
Did lots of work on this a while back at Barrus.

4 strokes and Optimax on average 33%-40% better on fuel than a conventional 2 stroke engine. But only downside with the Opti/Etec is you still need to put 2 stroke oil in which is worth factoring in!
Agree with Turbo, However 4 strokes take oil too which is changed annually or more and in our experience our Opti's cost no more in oil !!
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Old 02 June 2011, 17:04   #10
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My experience
Last boat. 5m humber 90hp tohatsu carb 2 st. Average 0.7 litres/mile
New boat 6.5 xs rib 150Optimax Average 0.85 litres/mile. (Both statute mile)


Oil for the Optimax costs about 1.5 x standard oil for the tohatsu / mile
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