Yamaha hp rating how do they do it

[dnej]

Why is it, that the 40 & 50 hp Yammies, have the same displacement, and identical specs, yet different horse power, same goes for 60 and 70 hp models, identical in all specs, yet greater hp.Compression is the same. Whats the go?
Can you buy a 60 & make it a 70 sonehow?
David

[Spaniard_King]

They do it with caburation, exhaust Tuning and ignition timing or a combination of any of the before mentioned none of which shows up on the spec sheet :o

Garry

[Angla]

Mercury does the same. I think they all do it.
My 135 Optimax is a 2.5 litre the same as the 150 and 175 I'm pretty sure.
Angla ???

[Big_Kev]

It is commonly refered to as detuning.
A horsepower increase can be as simple as removing a restriction plate on some models.
Dose not stop selling of the higher horsepower for a lot more then the simple change is worth. :)

[dugong]

they all do it same donk but up to 3 different hp, i read once in F&B magazine that the 70/90 hp merc and 80/100 hp yammie 4 Strokes were all the same motor made by yammah just different tuning, the legs,gearboxes and cowels ect were made by each company.
also told by a mate in the trade that there is a 10% allowance in the hp and that you could get a motor right on the hp or better, he claimed yammie were usually right on the hp while the american motors were usually towards the higher end of the limit.
has anyone else heard of this???

[Black_Rat]

Difference in the current 75/90 Mercs I was led to believe was the revs the 90 revs higher hence a higher HP rating at the prop :-/

[logan_whiting]

the only thing that is different is the O ring in the carby ;) for a couple of $$$ you can make a 40 in to a 50