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| Motors Get the low down on which outboards perform best… |
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| Motors Get the low down on which outboards perform best… |
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#1
05-12-2011, 03:24 AM
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new motor advice.
Okay guys as some of you may of seen i have recently purchased myself a 2007 Stratos 275 that has a yamaha 90 on the back.
The 90 is okay i get 65ish KMPH but it is a little slow out of the hole and i would like to crack the 70K mark. I am planing to upgrade the motor and add a manual jack plate late next year but I dont want to over capitalise. The hull is rated to 125 HP so my first thought was a 125 Opti but at 17k I may be over doing it there. Are there any decent carb 2strokes out there in either 115 or 125. Any one have any recomendations either cheap or expensive? Thanks guys.
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Daniel Holder Field staff 
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#2
05-12-2011, 03:39 AM
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I feel you seem to be jumping the gun a bit.
Considering people said it was under powered, but here is what i would do 1st, elimnate all variables considering you mention you only want to gain 5kmh. a new motor to achieve this is over the top. 1. experiment with diffent size props. 1 pitch either way can increase hole shot and speed. but it also can decrease as well. 2. put on a manual jack plate. a 12inch jake plate may give you 5 to 10kmh extra. 3. simple evening out weight in the boat increases holeshot and speed. so move batteries around and trial it. 4. if you want to spend a heap of coin, I would go a Opti, but you will find it hard to buy a 125 opti. dont think they make them, thou i have been wrong before. dont rush in and over capitalise mate, experiment and enjoy what you have. Tony
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#3
05-12-2011, 04:37 AM
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Quote:
I can do the calc for you. I need ; prop pitch gearbox ratio Maximum RPM at WOT. Tony
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#4
05-12-2011, 04:42 AM
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I have your specs for the engine;
Engine Type 2-Stroke, In-line 3 Displacement 1140 cc Bore x Stroke 82 x 72 mm Recommended Max RPM 5000-5500 Lubrication System Oil injection Fuel Management Carb Ignition CDI Starter System Electric Alternator Output 12V - 10A with rectifier regulator Operation Method Remote control Trim & Tilt Method Power trim & tilt Digital Gauges Standard Gear Ratio 2.00 : 1 OEDA Emission Rating Need prop pitch. Do you have it? SHould be stamped on prop. Tony
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#5
05-12-2011, 04:47 AM
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I have calculated that with 5% slip (average) you can 'crack' 70kph with an 18" pitch prop!
This assumes you can get to max motor rpm of 5500rpm. With a 21pitch prop you will get over 80kph! Remember that more pitch slower off the mark!
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#6
05-12-2011, 04:54 AM
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sorry to intrude,
Tony, Gearbox: 1.64-1 Pitch 13 Rpm 5600 Merc 2 stroke and im looking for more top end speed and the prop cavitates in turns or when tubing\skiing... Top speed was 67km\h Last edited by boris; 05-12-2011 at 04:56 AM.
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#7
05-12-2011, 05:17 AM
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Quote:
If you go for say a 17" prop. Max top speed will be 87kph with no slip. Assume 5% slip you can get 84kph. These are theoretical speeds. A small hp engine will not have the power to push a large craft to these speeds nor will it have the power to push a large pitch. Hope this helps. For more advice see Ken at propgods.com
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#8
05-12-2011, 05:26 AM
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Thanks mate, i will look into re- proping it in the mean time.
I do still want to re power eventualy, with what i am not sure but the 90 is fine for now. May get that jack plate and prop though. Thanks guys
__________________
Daniel Holder Field staff
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#9
05-12-2011, 05:54 AM
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I wrote an article on this a while back.
First things first- there is no substitute for horsepower. These days I would only ever buy a boat with its max rated hp on the back. Saves repowering and upgrading later on. Secondly- propping performance boats like bass boats is essential to get the best from them. Not only prop design is important but also making sure outboard height is correct. I have had 4 new outboards (4th is coming in january actually) Here is my take on them. 30hp mercury 2 stroke- actually a re badged tohatsu model. Great motor. Would start first time every time even when cold and no choke. Would get one again in a heartbeat if I needed one that size. 50hp mercury 2 stroke carby model. A very poor excuse for an outboard. When it was running, it was good. But it had alot of issues such as stator coils, gearbox, choke issues etc. I repowered and was happy to see it gone. 90hp evinrude etec. This is the motor I should have put on my boat originally. Totally brilliant motor. No run in, used almost no oil, quiet, better on fuel than the 50 merc. New motor coming.... again another 90 etec. It says something if you buy the same motor twice I reckon. Carby two stroke motors are out of date technology that isnt worth worrying about IMO. I think merc only make 115 and 135 optis. They are a heavy motor too. Some people rave about them and I know someone who had a lemon. Evinrude make a 115 and a 115HO (high output) which performs like a 130. Probably the best option to get the most of the hull. Then you have tohatsu TLDI which are supposedly quite good too. You can go 4 stroke which are good on fuel, but your trying to use it as a ski boat as well and I reckon you will appreciate the power 2 strokes have out of the hole. Now about the jack plate... dont go and get one and bolt it on. You need to take the boat to a professional about this sort of stuff as you will want to have a water pressure gauge put on so you dont cook your motor. Hydraulic jack plates offer the best performance as you can adjust while on the water- manuals are a bit harder to do this. I have found quite a few outboard dealers to be pretty poor on their propping and knowledge on the subject. Better to go to a propeller expert. Also speak to the aus distributor of stratos- they might be able to suggest and assist with the proper setup.
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