Same motor different Horsepower?

[Rick1]

Same motor different Horsepower?


I have 2 motors- a 20 hp Yamaha and a 25 hp Yamaha,

Both have identical displacement, identical gearing and identical WOT of 5000 - 6000 RPM-

How can one produce 5 hp more?
No one seems to be able to answer this question - I think maybe the the 25has larger diameter carbs???

I know the same is true for 9.9 hp OMC & 15 hp omc - same displacment & RPM yet different power output.

How does one produce 25% more power? - I am perplexed?

I would be very curious to hear some answers

Thanks

 

[CATransplant]

Re: Same motor different Horsepower?

Normally, it is done by better breathing and larger carburetor venturi openings. Sometimes, the intake and exhaust systems are also different, to allow more air/fuel mixture to flow.

Typically, the more powerful version of the engine also reaches higher RPMs. What often happens is that a company will design the higher power engine, then detune it to produce less horsepower for a specific market segment.

What's odd is that the prices are different, even though the essential parts of the engine cost the same to make. Horsepower sells.

In some cases, as with the mid 70s Johnson and Evinrudes, the only difference was he carburetor.

It's basically a marketing gimmick.

 

[V4 Johnson]

Re: Same motor different Horsepower?

Exhaust components can also be a factor in increasing or limiting H.P.

 

[Silvertip]

Re: Same motor different Horsepower?

The same way a small block Chevy 350 can produce anywhere from 150 to over 500 HP. Same displacement. But different compression, different carburetion, different cam, different heads, different exhaust. It is very common for engine manufacturers to have two or three and even four HP ratings based on the same block. With two strokes however, exhaust tuning, porting, compression and carburetion are the main factors.

 

[asm_]

Re: Same motor different Horsepower?

Believe or not, the same market gimmick done on CPU chip for computers. Each chip coming off the lot are tested to see how fast they will run. Mfg try best to only mark chip to their nearest clock speed rating. But if there is more market demand on slower clock speed rating, they have been known to sell the faster chip at lower speed by adding either hard lock or software lock on the chip it self to limit its speed.

B

 

[Titanium48]

Re: Same motor different Horsepower?

It is much easier to overclock your CPU than it is to up the output of your outboard though.

 

[ondarvr]

Re: Same motor different Horsepower?

One reason the differences can be very small, or possibly even none existent in parts, is they are also allowed a 10% fudge factor on the HP rating. So a 20 and 25 may have very close actual HP figures.