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  1. #1

    Default "Old" HP vs. "New" HP

    I've heard it said that "older engines" had their HP rated at the engine whereas "modern engines" rate HP at the prop.

    Is that true?

    ...and if it is true, how do you compare?

    For example, my boat has a 1969 25HP Evinrude, and it is just a wee bit under powered. An older 40HP would be nice....but maybe I should look for a newer motor. Is an "older" 40HP like a Modern 35? Modern 30? Modern 25? If an older 40HP would be good, what size "modern" engine should I be looking at?

    ps: I'm thinking a modern 2-stroke, not 4-stroke
    Last edited by boatbuilder57; 10-04-2017 at 09:49 PM.

  2. #2
    Join Date
    Nov 2005
    Location
    Mt. Zion, Illinois,
    Posts
    528

    Default Re: "Old" HP vs. "New" HP

    You are correct. There was a time when engines were rated for HP at the crank then later the dyno tests were performed at the prop. I seem to recall that change took place somewhere around 1980.

    What is the maximum HP rating for your boat? That's really the better place to look so you know your options for a re-power. Personally I tend to prefer 'newer' engines with CD ignitions rather than points. I think that break was somewhere around 1974 or '75 when the change was made to the CD ignition. The old points ignitions can and do work just fine so for me it's a preference thing.

    Depending on the size of your boat, one of the mid-70's or later 40HP or 50HP engines can push you along at 30+ MPH.

    KJ

  3. #3

    Default Re: "Old" HP vs. "New" HP

    Well, the boat is "home made", so there's no builder's plaque......but the plans (from the '50s) state 70HP max. Here it is with a 1969 25HP. It scoots right along at about 22MPH, but a 40HP would get it up on plane a bit quicker.

    I'm thinking a modern Evinrude E-Tec 30HP would out-perform an "old" 40HP. Does that seem logical?





    Here it is with a '53 Evinrude 15HP, which was too small for the boat.


    Last edited by boatbuilder57; 10-05-2017 at 08:23 AM.

  4. #4
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    3,541

    Default Re: "Old" HP vs. "New" HP

    Basically you can use what you want depending what your overall performance needs are. There is not much difference in ponies rated at the prop or the crank the newer engines are a bit lighter as well. Unless your thinking four stroke the engine weight is a factor. What ever you decide you need the proper prop for your setup HP is 100% rpm relative plus it will increase the service life of the engine. If you want faster go bigger if you go bigger it drinks more fuel.
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