1986 Super Sport 15 Engine Choice

[Cboyar]

Q1: for re-powering [what was later clarified to be a1986 Super Sport 15], which engine is the best choice?

[When answering Q1, consider these conditions:]

• I think the Yamaha 70-HP two-stroke-power-cycle engine, weighing 228 lbs was the best-ever engine for a 1985-1993 15-foot Super Sport.
• I have narrowed down my choices to a 2025 Mercury 60 ELPT or a 2025 Mercury 75 ELPT. Service, availability and significantly lower cost ($3,000 to $4,000 less than a 2025 Yamaha F70) have influenced my decision.

Q2: assuming that a 2025 Mercury is the best choice, should the "new Merc" be a 60-HP ELPT or a 75-HP ELPT?

[When answering Q2, consider these conditions:]

• the 2025 Merc 60-HP ELPT is 112-lbs lighter than the 2025 Merc 75-HP ELPT, 247 lbs. vs 359 lbs;
• the 2025 Merc 60-HP ELPT is the highest power rating of the mid-range line;
• the 2025 Merc 75-HP ELPT is a de-tuned 90 and 115-HP ELPT;
• the 75-HP exceeds the maximum power rating of the 1986 15 foot Super Sport.

[LIMITATION FOR Q3:
ONLY FOR PEOPLE WHO OWN a 1985-1993 15-foot Super Sport or similar configuration, and have re-powered with a Merc 60-HP FourStroke or a Merc 75-HP FourStroke:]

Q3: what do you like about your choice of engine?

Q4: what do you not like about your choice of engine?

All help is appreciated.

[Moved to the PERFORMANCE forum for discussion. Originator of thread has been notified of the change. Original version of this post was later modified by the original author to supply much additional information about the boat and the engines that were being mentioned and for which advice was being sought--Moderator]

[jimh]

It is good you revised you initial post to give the model year and the model configuration of the "15-footer" you were asking about. Without knowing the model year and the model configuration of the 15-footer, giving a reasoned answer will be difficult.

It is good you revised your initial post to specify the model of the new Mercury engines and their weights. Without knowing the actual weights of the "new Merc" 60-HP and 75-HP engines, giving a reasoned answer will be difficult.

In general, too much engine weight should be avoided, particularly on small hulls like a 15-footer.

If you are asking about the classic era 15-footer introduced in 1976, a consideration for the early production hulls was their rather light weight, due to a rather light lay-up of the hull.

For early classic-era 15-footers [1976 SPORT and similar models], adding a heavy engine that exceeds the hull power rating would probably not be a great choice--unless your principal interest was operating the boat at the highest possible speeds and you would not be concerned about loss of freeboard at the transom and a marked tendency for the boat to be trimmed down by the stern.

Your statement that a particular engine, who cost is $4,000 less than other options, becomes a difficult factor to ignore, tends to indicate that the engine cost is an important factor in your decision. On that basis, you probably should buy the engine with the lowest cost. Among the limited choices, the "new Merc" 60-HP is probably the "best" choice due to lowest cost among the limited choices.

ASIDE
Assuming that cost is an important consideration, you may want to look at other brands, such as SUZUKI engines, which are known to be very competitive on cost and are considered of equal quality.

[jimh]

Comparing the “ideal” legacy Yamaha 70 weight at 228-lbs to the Mercury 75 ForeStroke at 359-lbs, the 131-lbs increase in engine weight seems quite significant.

The Mercury 60-HP FourStroke at 247-lbs is only 19-lbs heavier than the legacy 70-HP Yamaha. The 60-HP model will also cost less than the 75-HP engine.

The SUZUKI [DF60] weighs 229-lbs and is 130-lbs lighter than the Mercury 75-HP engine.

[Moderator's note: corrected typo "DF70". corrected to DF60.]

[Phil T]

The Yamaha F70 is the ideal engine for that hull.

[jimh]

In the initial post, the author mentioned that the legacy Yamaha 70-HP two-stroke-power-cycle engine was the "ideal" engine for the classic SPORT 15 hull. That engine weighed around 231-lbs (according to what I can find). There have been many engine weights mentioned in this thread. To make the engine weight range easier to understand, here is list, sorted by weight, from lightest to heaviest, and noting the weight increase compared to the lightest choice as the engines get heavier:

• 229-lbs --> Suzuki DF60 lightest
• 231-lbs --> Yamaha 70-HP two-stroke-power-cycle +2
• 247-lbs --> Mercury 60-HP FOURSTROKE +18-lbs
• 253-lbs --> Yamaha F70 +24-lbs
• 359-lbs --> Mercury 75-HP FOURSTROKE +130-lbs

[Moderator's note corrected error in listing the Suzuki DF70 instead of DF60. The DF70 is much heavier.]

This comparison shows clearly that the any of the first four engines would be a good choice, as the weight difference between the lightest and the heaviest is only 20-lbs. The fifth engine, Mercury 75-HP FOURSTROKE, is clearly the outlier, as it is 128-lbs heavier than the lightest engine.

[17standard]

I think the correct weight of the Suzuki DF70 is 341-lbs. [Yes, that is correct; the error in the comparison above was a typo of "DF70" instead of DF60 in the list of engine weights. The DF60 is a light weight three-cylinder; the DF70 is a heavier four-cylinder engine.]

ASIDE
My plan is to re-power [a completely different boat, a 17-footer]. For my application the engine price and weight are a consideration--not top speed--and therefore I am considering a 60-HP engine.