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Author Topic:   Re-power with 2-stroke or 4-stroke
mhawk153 posted 02-14-2004 03:30 PM ET (US)   Profile for mhawk153   Send Email to mhawk153  
I have a 1979 SPORT 15 that I am considering re-powering; it currently has a Yamaha 70 (2-stroke), the max rated horsepower for the boat.

Would the added weight of a 4-stroke 70-75 be too much?

I thought about a 60-HP 4-stroke. How much get up and go would I really lose with that engine (besides the obvious 10 less horsepower)?

Thank you for your help.

David Jenkins posted 02-14-2004 09:54 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
I have a 15 with a 70 hp 4-stroke. It is fantastic. I'm in Durham, not far from you. I'd be happy to take you for a test drive.
mhawk153 posted 02-16-2004 05:31 PM ET (US)     Profile for mhawk153  Send Email to mhawk153     
Does the added weight of that 4-stroke make the stern sit lower in the water?
Bigshot posted 02-17-2004 03:54 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I would go with the 60hp Merc for weight considerations. The 60-70hp Johnson/Suzuki are almost 100 lbs heavier at 350 lbs or so. The 70 Yammie is not as powerful as the 70 OMC 2 stroke so I think you will be happy with the 60 4 stroke.
rbruce posted 02-22-2004 10:11 AM ET (US)     Profile for rbruce  Send Email to rbruce     
I am also partial toward 2-stroke engines for three reasons: power to weight ratio, price, and ease of maintenance.

If emission compliance is too much to bear in your conscience please consider that direct injection two strokes are there to fill the void. Not having a valve train and controlling emissions of NOX through proper timing of the injection of gasoline and oil separately makes me feel that the microprocessor era has reached the venerable two stroke and simplified the inherent complications of the 4 stroke.

Optimax by Mercury, Yamaha HPDI (High Pressure Direct Injection), Tohatsu LPDI (Low Pressure Direct Injection) and FICHT,E-TEC by Bombardier are the ones to follow in terms of power to weight ratio, I am not convinced absolutely in ease of maintenance but these at least do not have a valve train to consider in the up keep and are covered in comprehensive maintenance agreements and warranties, also by trained mechanics using sofisticated computerized diagnostic systems.

In your boat the less weight in the transom translates in more weight for equipment and passangers and this applies to all of the possible applications that you give to your boat be it tourism, fishing, skiing, etc.

All modern two strokes feature oil injection which appears to work correctly in properly maintained motors, I am not sure if in old used motors. Premix is no problem for me as you can always make the correct arithmetic to establish the proportion of oil to gas.

Have good hunt for your new motor and keep us posted on your discovery!

lhg posted 02-22-2004 01:19 PM ET (US)     Profile for lhg    
Nick - Suzuki's new catalog now shows the dry weight of the 60's and 70's at 359#. Last year's catalog did not show weight. Yamaha is now showing their 75 & 90's at 11# heavier, 370#.
And the Merc 115 4-stroke is 27# heavier, at 386. I have noticed that the weight on all of the 4-strokes is without crankcase oil.
jimh posted 02-22-2004 03:06 PM ET (US)     Profile for jimh  Send Email to jimh     
In general when compared with a traditional high-emission 2-stroke engine like the one you currently have, a 4-stroke engine has these advantages and disadvantages:

4-stroke disadvantage
• weighs more;
• has more moving parts;
• needs more maintenance;
• produces less low-RPM torque.

4-stroke advantages
• gets better fuel economy;
• produces less emissions;
• runs more smoothly particularly at low speeds;
• does not smoke;
• will be perceptively quieter at idle and lower speeds.

The 4-stroke engine will cost more, too.

You can also find low-emission 2-stroke engines, and they have similar advantages and disadvantages compared to their Hi-E 2-stroke brethren:

2-stroke Low-E disadvantage
• weighs more;
• needs more maintenance;

2-stroke Low-E advantages
• gets better fuel economy;
• produces less emissions;
• runs more smoothly particularly at low speeds;
• does not smoke;
• may be quieter at idle and lower speeds.

The 2-stroke Low-E also costs more.

If you wait about 18 months you will not have the option of buying a new 2-stroke Hi-E outboard in the United States. Manufacture of such engines in the United States is prohibited after 2006.

In the case of the 4-stroke engines you will have to perform periodic oil changes of the crankcase oil every 100 hours or once a season at a minimum.

In the case of low-E 2-stroke engines you may have to change expensive spark plugs at regular intervals. Some of these plugs are $20 or more and may require careful indexing to install.

A recently introduced engine from Bombardier Recreational Products (BRP) is the E-TEC™ brand of outboard. This low-E engine has reduced periodic maintenance to a minimum. It is an entirely new line of engines and its field track record is unknown at the moment. On the face of its specifications it does merit strong consideration.

The Mercury 4-stroke engines are advanced designs with electronic fuel injection (EFI) and digital engine controllers. They also support advanced digital instrumentation (SmartCraft).

The current time is a good time to buy as almost all makers have offered incentives and extended warranty coverage for their engines.

Royce posted 02-22-2004 10:03 PM ET (US)     Profile for Royce  Send Email to Royce     
Great post Jimh! Sometimes you exhaust me with your throughness! Posts like yours make me want to sit back and only listen.
Bigshot posted 02-23-2004 12:50 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Even more reason to stress my opinion. 60 merc is light, costs less than the Yamaha and has all the advantages you need. I have to "slightly" disagree with ne thing in that Jim claims 4 strokes have lower low-end torque. Not true...thay have a flatter torque curve which gives that feeling but torque is actually higher on 4 strokes compared to 2....look at dirt bikes.

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