9.9 2 stroke vs 4

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Willson
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Boat Make: 3.4m zodiac
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MMSI Number: 10
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9.9 2 stroke vs 4

Post by Willson » 26 May 2018, 09:03

Could anyone share their experiences comparing the above engine sizes. Currently have a 2 stroke Johnson weighing around 35kgs giving a top speed of around 16-18mph depending on tide etc.
I would ideally like to keep to this size engine for the launching restrictions. Our boat is a 3.5 zodiac cadet.
I’ve been wondering what advantages in performance if any there might be.
:wavey

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Steve
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Re: 9.9 2 stroke vs 4

Post by Steve » 26 May 2018, 09:30

I would say that you're going to add weight with a 4 stroke, maybe around another 5kg on the dry weight. So the power to weight ratio will be lower and it'll be slightly slower to accelerate. I guess it'll also be slightly more complicated (expensive) to service.

On the plus side, you'll get the convenience of not mixing fuel (or buying oil), it'll be quieter, smoother and more fuel efficient.

I'm sure the other guys will share their experiences, but I would say the cost to change is more about convenience than out and out performance...

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Phil
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Re: 9.9 2 stroke vs 4

Post by Phil » 26 May 2018, 09:40

Willson wrote:Currently have a 2 stroke Johnson weighing around 35kgs giving a top speed of around 16-18mph depending on tide etc.
If you’re looking for more performance, do you know if your model of Johnson has the same engine block as the 15hp?

My Johnson GT10 2-stroke was sold as a 10hp. Alan at F-RIBs SE had a restricter plate in the carb removed before I bought it off him, which unleashed the full 15hp the engine is capable of :).


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F-RIB 360 with F-RIB wheels, seat cushions and bag and Scotty rod rests
15hp 1992 Johnson GT 10 2-stroke

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Andy B
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Re: 9.9 2 stroke vs 4

Post by Andy B » 26 May 2018, 10:23

My mariner 9.9hp 4 stroke weighs 38kg's I would say it's about 2mph slower than my old mariner 9.9hp 2 stroke.
Hole shot is about the same and the mid range is far more usable on the 4 stroke.
Fuel wise the 4 stroke uses less than half the fuel my 2 stroke did. In fact in Scotland it pushed my 380 Zodiac loaded with gear all day long at 15 knots and still returned over 4 miles to the litre.
Life on the water with a 4 stroke is far nicer, no noise or smell.
Steve wrote:I would say the cost to change is more about convenience than out and out performance...
What he said :thumbsup
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Willson
Newish Member, But I Like It Here
Posts: 13
Joined: 10 Sep 2017, 07:00
Boat Make: 3.4m zodiac
Outboard: Johnson 9.9 2 stroke
MMSI Number: 10
Location: North Wales
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Re: 9.9 2 stroke vs 4

Post by Willson » 26 May 2018, 22:02

The current Johnson is a 1999-2000, from some quick research it requires a larger carb and exhaust. If I could get the engine breathed on a little then that might do the trick. I’ve been keeping an eye out for parts for a while. But they haven’t appeared :roll:
Having a newer engine appeals to me. But ours has been very reliable.

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