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  1. #1

    Engine Height on Xpress H18

    So I have an Xpress H18 with a Yamaha F115 and a 6" manual Jackplate. I am looking into adjusting the motor height but I'm not totally sure what a good height is. I know that every boat is different, but maybe if I could get some info on a good starting point. I measured the engine height. With the engine trimmed about level with the bottom of the boat, the Cavitation plate is about 2.5" above the bottom of the boat, the prop shaft is about 4 5/8" below the bottom of boat.

    The reason I'm asking about adjusting is that I can run about 5800 RPMs alone, and I can get about 5600 if I add another passenger and their gear. Could finding the sweet spot on engine height get me closer to the 6k max RPM? I'm currently running a 19 pitch prop, I know dropping down to an 18 or 17 would make up the RPM difference, but I'd like to mess with engine height first since its simple enough to adjust the jack plate.

    Troy

  2. Member
    Join Date
    May 2015
    Location
    Iowa
    Posts
    119
    #2
    I have a different set up with a Merc 150 but I'm around 3 1/2 to 3 1/4" from center of prop to pad. If I was you I would definitely move the motor up before trying to re-prop. I would say start at 4" below pad and work up from there a 1/4" at a time. You'll want a water pressure gauge (if you don't have one) to make sure you don't cook the motor.
    2008 XPRESS H18
    2017 MERC 150 4S

  3. #3
    I will start with that. I kind of thought the motor seemed a little bit low, so I'm glad you agree. Thanks for the info. I do have a water pressure gauge. Would anyone happen to know what is the lowest safe water pressure I need at WOT on the F115?

  4. Member
    Join Date
    May 2015
    Location
    Iowa
    Posts
    119
    #4
    What prop you have also makes a difference on engine height. Personally I like the way a Trophy Plus performs on my boat. It was recommended by a few people on here. As for water pressure I don't know. I'm sure someone will chime in.
    2008 XPRESS H18
    2017 MERC 150 4S

  5. Member
    Join Date
    Jun 2014
    Location
    Auburn, AL
    Posts
    94
    #5
    Quote Originally Posted by Troy1985 View Post
    I will start with that. I kind of thought the motor seemed a little bit low, so I'm glad you agree. Thanks for the info. I do have a water pressure gauge. Would anyone happen to know what is the lowest safe water pressure I need at WOT on the F115?
    From Yamaha:
    Attached Images Attached Images

  6. #6
    Thanks for the picture. I am currently getting almost 30 PSI at WOT. I'm going to raise it up to 4" to start and see what happens.

  7. Member
    Join Date
    Sep 2012
    Location
    Thibodaux
    Posts
    302
    #7
    Keep raising up until you get 15 psi constant pressure at wot. On my old H18 I was all the way up on my plate
    2010 Xpress X-19 2010 Yamaha VMAX Series 2 200