What is my motor's true hp?

[wmbreck]

I have a 1992 Johnson 28 SPL motor in nice condition. But I have read once or twice somewhere on the forums on upgrading that, because of a horsepower rating change back then, that my motor motor is about the equivalent of the previoulsy rated 35 hp and that the 20-35 hp versions were pretty much the same internally except for carberation for the most part. Does anyone know if there is any truth to this or not?
It is not that it really matters, but mentally it might 'seem' to feel faster if true

Thanks!

 

[86 century]

Re: What is my motor's true hp?

There was a rateing change in the mid '80 so it maybe about the same as an older 35.

The change was where they test the hp changed from crank to prop shaft so you gaine around 10% on anything made after the change.

 

[Handyman1]

Re: What is my motor's true hp?

Hi beck up until 1984 the north america motors hp were measured at flywheel so they switched to prop hp by 1986 so basically your motor was a 35hp motor in 1984 in 1986 became 28 hp the Mercury and the Japanese motors were measured at prop prior to 1984 so now all the motors are measured at prop there is a 5-8% loss between flywheel and prop

 

[JB]

Re: What is my motor's true hp?

Making it far too complicated and confusing.

The 28SPL is a 30HP without VRO or PT&T. It was "derated" in order to produce an entry level outboard in that price range.

The change to HP rating at the prop, rather than the flywheel took place 7 years before your engine was made and has zero to do with the 2HP "difference". There is actually no 2HP difference. The 28SPL is a 30HP outboard.

 

[seahorse5]

Re: What is my motor's true hp?

As JB said, your motor is a 30hp but it will not perform as well as a 30. Being an economy priced motor it does not have the efficient thru-hub gearcase or propeller design. It uses the older style 18-20-25hp 2 piece gearcase and a prop that uses a drive pin to turn it.