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Old 23-12-2010, 14:26   #1
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How Can I Increase Horsepower Effeciently ?

A mechanic friend told me that there is a way of increasing power efficiency in relation to the horsepower of an outboard engine, being a little tricky, the experts can give some opinions.
For example a 1997 90hp 3 cylinder Mercury
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Old 23-12-2010, 14:33   #2
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What do you mean by power efficiency? If you are thinking about upping the hp, forget it, you will wreck a perfectly good engine. If you are talking about the delivery of that power, a stainless steel prop will make a small difference.

However, if you really want to make a big difference to the boat, stick a V6 on it

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Old 23-12-2010, 14:54   #3
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Some family of motors use the same block But the porting and carbs are different Not always easy to upgrade
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Old 23-12-2010, 16:15   #4
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Efficiency is a function of the available HP minus the frictional and other loses that rob that available HP from the prop.
They include these small easy to do items.
1- Use friction modifiers in all oil areas like the gas & oil if it's a 2 stroke.
2- Use friciton modifiers and synthetic oil in the thinnest that's acceptable to use in your environmental conditions.
3- Best gap on plug(s) for the tune-up.
4- Clean all debris and buildup off the lower unit that sees the water flow around it.
5- Use the best gas you can as far as octane rating goes and then take adbantage of it and advance the ignition timing "slightly".
6- Make sure the vessel it's pushing thru the water is balanced and loaded properly and the bottom is clean and you're not dragging anything to slow you down.
7- Make sure the air cleaner is as clean as it can be and the proper size without restrictions to air flow.

and for those seeking to increase efficiency during an overhaul...

1- As stated above, port & polish to the head.
2- All of the above.

There's a lot more things I'm sure people will post but these are the ones that come to mind immediately for me.
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Old 23-12-2010, 16:55   #5
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Denny, you didn't leave much.

let's seeeee, how aboooout .............. oxygen, more oxygen! Yeah, that's it! and and nitro.
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Old 24-12-2010, 07:48   #6
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Thanks for the replies,
I refer to the efficiency of development, might increase the horsepower, but the convenience and comfort of a 2-stroke engine, even though it is more noisy compared with a 4 stroke.
As a fan for the 2-stroke and consumption is not a problem because I make my boat my way of fun with family on weekends.


sorry for my bad English.
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Old 24-12-2010, 08:42   #7
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some of the 9.9 hp outboards were detuned 15hp outboards. this was done to get under the 10 hp limit of many small inland lakes. Fairly easy conversion to 15hp from these particular 9.9 motors

many diesel engines have different ratings depending on whether they have a turbo or not and different injectors can make a difference in hp/fuel efficiency of some diesels
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Old 24-12-2010, 09:01   #8
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Originally Posted by gettinthere View Post
some of the 9.9 hp outboards were detuned 15hp outboards. this was done to get under the 10 hp limit of many small inland lakes. Fairly easy conversion to 15hp from these particular 9.9 motors

many diesel engines have different ratings depending on whether they have a turbo or not and different injectors can make a difference in hp/fuel efficiency of some diesels

I had one of the Yamaha 9.9s that was the same size/weight as the 15 and supposedly could be converted easily. This was a long time ago and some loss in memory detail is apparent to me.

My search of the diagrams provided by a nice local place and reviewed by their owner and mechanic showed that some parts were easy. The reed valve plate being one I remember.

But the big part was that the block was machined with smaller apertures (?) and to change that.........well.........you can figure that out.

I have often heard this asked and discussed but have never been told by or heard of (details) anyone that has actually accomplished it.

In my case (Yamaha) I think they are/were smart enough to know that if it was easily done with a few parts they would sell very few 15s and a lot of 9.9s and reed valves. See, I bought the 9.9 because I could not afford the 15.
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Old 24-12-2010, 11:17   #9
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some of the 9.9 hp outboards were detuned 15hp outboards. this was done to get under the 10 hp limit of many small inland lakes. Fairly easy conversion to 15hp from these particular 9.9 motors ...
I'll venture to say that it's much easier to say, than to do.

Quote:
Originally Posted by Therapy View Post
... I have often heard this asked and discussed but have never been told by or heard of (details) anyone that has actually accomplished it ...
Indeed.
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Old 24-12-2010, 12:25   #10
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I did swap the carb on my 2 cycle 9.9 merc to a 15. The engines are otherwise identical. Yes, I can tell the difference, higher power higher gas consumption. However, getting a 50% increase in power did not cost me a equivalent increase in consumption. Biggest difference is how quickly the dink comes up on a plane.

Unfortunately, this doesn't address Algarve's problem.

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Old 24-12-2010, 12:53   #11
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As the old saying goes speed costs money how fast do you want to go?
I think most modern engines are power limited by the electronic engine controller, some engines can be reprogrammed but many can not.
I would buy a bigger engine or just enjoy what you have and just give it a good tune keep the bits in the water clean and most importantly make sure you have the correct prop pitch.
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Old 24-12-2010, 14:15   #12
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I've also loved Maxwell over the years (had several on different boats). One important thing that Maxwell does well is to not mix different metals. Too many others slip in a piece of aluminum or two with a stainless screw and the corrosion takes off.

My current windlass is a Maxwell Liberty. It has the nifty feature of an emergency manual geared drive with a winch handle. I've never needed to use it but I once tried for fun. No problem lifting a 100 pound anchor and 3/8 chain.

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