Horsepower question

[Jake N]

Sorry that this is in the wrong forum but I couldn't find where it fits:

How does my 1974 20hp Mercury outboard compare horsepower wise to new motors? I realize that they used to rate motors at the crank and now they rate them at the prop, but how much power is lost through the gears?

Would my motor rate 15hp on today's standards?

The reason I'm asking is because I would like to upgrade motors but I'm unsure what to put on the boat to get it where I want to be. It's a 13 1/2' fiberglass duckboat and it could use a little more pep than my '74 20hp Merc is willing to give it.

Thanks in advance.

 

[emckelvy]

Re: Horsepower question

A newer, "prop-rated" 20 HP would be somewhat 'zippier' than your old motor.

Figure something like 10 to 15 percent diff in crankshaft and propshaft hp ratings.

Just depends on how much more "pep" you're looking for and what your boat is rated for max HP.

If it'll take a 25, you'd probably note a significant increase in performance over your 20.

Many 25's nowadays are just "amped-up" versions of the 20HP model so you'd see no diff in weight. But a lot of extra beans at the top end.

HTH............ed

 

[Jake N]

Re: Horsepower question

Thanks for the input. I'm not sure what the boat is rated for as it is pretty old (mid 70s) and no longer has that information on it.

A buddy has a similar boat with a newer 25hp Suzuki that blows the doors off of my boat.

 

[emckelvy]

Re: Horsepower question

If you think the boat will handle it and the transom's in good condition, the 25 would be a good choice.

Probably not a lot of price diff between a new 20 and 25 at any rate.

 

[Jake N]

Re: Horsepower question

Is there an easy way to upgrade my 20hp to 25hp, or otherwise gain some ponies for my old motor? I rebuilt the carb myself so I'm not entirely clueless when it comes to the motor.

Thanks again for the info.