Johnson Seahorse: old vs new 28HP

[Jgreen12]

Any idea what a 28HP 1962 Johnson RX-10 converts to today's Horsepower? Would it be more? Less? I know that I need to use synthetic at a ratio of 24:1 but as for the power people have differing opinions on what horsepower it would convert to in today's standards.

 

[HighTrim]

Re: Johnson Seahorse: old vs new 28HP

The hp was rated at the crank back then, compared to at the prop nowadays. So obviously your 28 crank hp is less at the prop. I have heard several ideas on mechanical hp loss through friction, etc but have never actually dynoed one to see for sure exactly what that loss is.

 

[HighTrim]

Re: Johnson Seahorse: old vs new 28HP

...also that is a jeweled motor, and can be run at 40:1, as are most 60-64 bigger hp motors, 18hp and up. That is personal preference though, and you should do what makes you feel comfortable.

 

[Jgreen12]

Re: Johnson Seahorse: old vs new 28HP

Is it weak enough that I can effectively use it as a trolling motor?

 

[HighTrim]

Re: Johnson Seahorse: old vs new 28HP

The difference is roughly 10%, not 90%

If it is tuned right it should idle down nice.

 

[F_R]

Re: Johnson Seahorse: old vs new 28HP

Never having done a personal comparison, my bet would be that the new 28 will make the old one look bad, both at high and slow speeds. At least that is the case with the 35hps which I do have personal experience with.

 

[Jgreen12]

Re: Johnson Seahorse: old vs new 28HP

Awesome, thank you. I will play with the oil to gas mix. I have been told only 24:1 but... I really want to see what 40:1 will run.