Yamaha Horsepower 20hp vs 15hp Identical Specs?

[TheWaterDog]

Hey All,

Hoping someone can clarify something.
Please see specs below. Specs were taken from Yamaha website.

How can specs be identical between a 20hp and 15hp motor? Where is the extra 5hp coming from for the 20hp motor? http://yamahaoutboards.com/outboards/Portable/comparisons

	Yamaha Portable F20	Yamaha Portable F15
Engine Type	2 Cylinder	2 Cylinder
Displacement	22.1 ci (362 cc)	22.1 ci (362 cc)
Bore x Stroke	63 x 58.1mm (2.48 x 2.29 in)	63 x 58.1mm (2.48 x 2.29 in)
Compression Ratio	9.3:1	9.3:1
Prop Shaft Horsepower	20hp @ 5500rpm	15hp @ 5500rpm
Full Throttle RPM Range	5000 ~ 6000 rpm	5000 ~ 6000 rpm
Fuel Induction	SOHC	SOHC
Intake	Carburetor	Carburetor
Exhaust	Through Propeller	Through Propeller
Cooling	Water/Thermostatic Control	Water/Thermostatic Control
Ignition	CDI Micro Computer	CDI Micro Computer
Spark Plug	DPR6EB-900-000	DPR6EB-900-000
Alternator Output	10A **	10A **
Starting System	Manual or Electric	Manual or Electric
Lubrication	Wet Sump	Wet Sump
Engine Oil Capacity	1.8L/1.6L w/without filter	1.8L/1.6L w/without filter
Recommended Engine Oil	Yamalube[SUP]?[/SUP] 4M (See owner's manual)	Yamalube[SUP]?[/SUP] 4M (See owner's manual)
Recommended Fuel Filtration	Yamaha Mini 10-Micron Fuel/Water Separating Filter (external)	Yamaha Mini 10-Micron Fuel/Water Separating Filter (external)
Recommended Fuel	Regular Unleaded (Minimum Pump Octane 87)	Regular Unleaded (Minimum Pump Octane 87)
Ethanol Blend Limit	10% Maximum	10% Maximum
Gear Ratio	(27:13) 2.08:1	(27:13) 2.08:1
Gear Shift	Forward, Neutral, Reverse	Forward, Neutral, Reverse
Shaft Length	S=15" L=20"	S=15" L=20"
Degree of Tilt	67?- 71?	67?- 71?
Degree of Trim	4 positions	4 positions
C.A.R.B. Rating	3-Star	3-Star

Thanks,

TheWaterDog

 

[GA_Boater]

Welcome aboard.

Could be cam, carb, timing or anything else to hot rod a 15 to a 20. The only way to be sure is to compare part numbers.

 

[Scott Danforth]

the 15 is a detuned 20 for the reasons GA_Boater mentioned

 

[ajgraz]

This brings up a question in my mind...

In the poster's example, the same block, etc. is used between a 15hp and a 20hp. Another example might be a manufacturer who uses the same 1.5L block for a 75, 90, 115 and 125hp rating. (Obviously this keeps manufacturing costs down--but also improves parts availability for us!)

So the question: is the manufacturer really "hotrodding" a "lower-spec'd" block into a higher hp block, OR are they actually "detuning" a "higher-spec'd" block into a lower hp?

Seems to me like the former might be cheaper for the manufacturer, while the latter would surely be safer and more durable for the user...

 

[TheWaterDog]

Thanks for your posts! Sounds like it is worth the research to find the real answer. Buy a 15hp and save $1000. Maybe swap out a part for $250 for the upgrade.
Any mechanics in the forum have the resources to do the research?

 

[ondarvr]

Sometimes the conversion makes sense, but most times it doesn't, you just need to examine the part numbers very closely to know. You also have to look at the issue of voiding the warranty, some people want the warranty, others don't care.

​The other thing to look at is there's a fudge factor in HP ratings of + or - 10%, so the true difference in HP may not be as much as you think.

 

[jimmbo]

Might be different cylinder head/valves, and/or as mentioned before, carb, cam.

 

[ondarvr]

Any mechanics in the forum have the resources to do the research?

​You do, google a parts a diagram and get out a note pad.

 

[ronaldj]

Just so you know
The Suzuki 9.9, 15 and 20hp EFI 4 stroke outboards all use the same block and have the same weight
It appears that's the way the market is headed
Of course that makes one wonder why you would buy the 9.9 over the 20 unless the difference in price was huge or you fished someplace where they were actually savvy enough to tell the difference between a 9.9 and a 20

It also makes you wonder if you void your warrenty if you swap the 9.9 controller for a 20

 

[ondarvr]

Yes you would void the warranty.

​A manufacturer can easily change the HP on an EFI engine buy changing the programming, no other part differences may be needed, but might be.

​The market has been doing that since the 50's or so, same block and 99.9% of the same parts can cover a large span of HP ratings.

​People already try to fudge on HP in regulated areas, if they decide to enforce the rule they check the model # on the motor....busted! No difference here.

Modifications like reprogramming would be a little harder to detect.

 

[ronaldj]

Yes you would void the warranty.

​A manufacturer can easily change the HP on an EFI engine buy changing the programming, no other part differences may be needed, but might be.

​The market has been doing that since the 50's or so, same block and 99.9% of the same parts can cover a large span of HP ratings.

​People already try to fudge on HP in regulated areas, if they decide to enforce the rule they check the model # on the motor....busted! No difference here.

Modifications like reprogramming would be a little harder to detect.

I am in no way advocating this but
Based on what you said
It seems like you would get the 9.9 to use on lakes and reservoirs where they check and then replace or reprogram the chip so you could gain your 10hp for use in saltwater

 

[ondarvr]

If, and I say if because I have no idea, the only difference is the programming, then you would probably need to swap computers, they may not be reprogrammable to that extent by the owner. You would need to pull up the parts list for each motor and start comparing #'s to know if programming is the only difference.