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Old 11 December 2008, 03:27   #1
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gear/drive ratio

greetings everyone!!i have a question about gear ratio.I noticed that there is a significant difference between 4 stroke and two stroke gear ratio.today I red on suzuki site that new 70,80,90 outboards have powerfull drive ratio 2.59/1.my e-tec has 2.0:1,while yamaha 100 has 13:30.can someone explain what does it mean for engine performances etc...
thx!!
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Old 11 December 2008, 05:09   #2
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Stype,

Firstly, welcome to Ribnet!

Gear ratio is too wooly a comparison unless you compare it alongside the prop & the engine power / torque curves. The gear ratio just tells you that the engine shaft is going X% faster than the prop shaft, but the prop pitch (think of it as your final drive ratio on a car) can then be the equivalent of gearing it back down or gearing it up further..... Also the diameter of the prop has a big influence on the torque needed to spin it at a given rpm.

The gear ratio will have been chosen to optimise that particular engine powerhead and the range of props available for it. I won't bore you with the prop pitch explanations- there's oodles been written about it in the forums, a search will keep you amused for hours.....

I'll leave the prop experts to explain the "gearing" effect of the prop and what happens when it spins too fast in better detail......

Apologies if the answer isn't as direct as you'd hoped, but I wouldn't loose any sleep over it unless you plan to start racing Cookee!
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Old 11 December 2008, 05:37   #3
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thank you 9D280!!the reason i m asking this question is comparison between 4S and 2S engines.
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Old 11 December 2008, 08:00   #4
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Stype,

Firstly, welcome to Ribnet!



Apologies if the answer isn't as direct as you'd hoped, but I wouldn't loose any sleep over it unless you plan to start racing Cookee!
That would be me then - the reason for different gear ratios is simple, it is so that you can run similar sized props on a wide variety of rev limits. Generally 2 strokes rev faster than 4 strokes, but they would both run 19 to 23 inch pitch props.
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Old 11 December 2008, 12:31   #5
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thank You cookee
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Old 12 December 2008, 09:02   #6
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thank you cookee
:d
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