Merc 115 Pro XS WOT - Fuel Pressure

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Capt Jim
    replied
    Again, thank you. And that is the one thing I know is different between my boat and his. His outboard is actually one bolt hole lower. He's in the number one hole. I'm one hole up and confirmed with HB that's where they mount the 115 Pro XS. None of this makes sense. I'll run that Spitfire X7 17" by the weekend. I'll post some numbers then.
    Last edited by Capt Jim; 10-20-2020, 11:20 PM.

    Leave a comment:


  • ken2
    replied
    You would think a bowlifting prop would make it hop worse, but as with everything in boats, nothing is set in stone.
    i've seen boats that porpoised horribly with 4 blades and 3 blades actually held the bow up at speed and ran great, Its rare, but it happens.
    Same thing with height, 9 times out of 10, the guy with a porpoising boat has the motor too low, but I have seen it go the other way many times too. guy lowers it down and it fixes it.
    With boats, you just have to try it, everything varys.

    Leave a comment:


  • Capt Jim
    replied
    My bad. He's running the regular 2.07 lower and it's a Trophy Plus prop, not the Fury. As for the Laser 2 and correct me if I'm wrong; but, shouldn't a bowlifting prop aggravate the porpoising? Also, thanks for your time and energy on this. It's greatly appreciated.

    Leave a comment:


  • ken2
    replied
    There are certain boats that actually need bowlift, so a sternlifting prop may not be what it likes.
    the Laser 2 is definitely a bowlifter.
    sounds like the other guy might be running a Command thrust gearcase though if he's turning a Fury 4, as that is a full size prop.

    Leave a comment:


  • Capt Jim
    replied
    Ken, a litle update here. I had the chance to try an SCD4 18" Up to about 4500 RPM's, it was faster than the 18" Vengeance. Above that, the Vengeance pulled away. The bad part is, the SCD porpoised twice as bad as the Vengeance! I believe there's more speed; but, putting the tabs down to control porpoising was like hitting the brakes. I thought the SCD was supposed to help alleviate the porpoising. Also, couldn't get the SCD4-18 over 5700 RPM's

    Secondly, spoke to another Marquesa owner with almost the same setup. Merc 115 Pro XS, 3 AGM batteries and twin power poles. Runs either a 3 blade 19" Laser ll or the 4 blade 19" Fury. Spins both up to 6000 RPM, with the Laser ll pulling a little more and a little more speed.

    Thoughts?

    Leave a comment:


  • Capt Jim
    replied
    Hell's Bay is supposed to be getting me a Spitfire in 17". Let me pull some numbers with that and we'll see if Power Tech's SCD is a better fit. Thanks for your help.

    Leave a comment:


  • ken2
    replied
    The SCD3 is closer to the Yamaha painted stainless, less bowlifting, easier to turn.
    Depending on how the boat runs, you could go either way.
    if the boat wants to porpoise easily and doesn't like a lot of trim, I'd go SCD3
    if it likes bowlift, I'd go PTR3. (closer to the Talon)
    with either, I think 16 pitch would be a better option to get your RPM up, and low 40's is probably all its going to get with the extra batteries and powerpoles, and trolling motor.
    but we could try a 17 and see if you can turn it.

    Leave a comment:


  • Capt Jim
    replied
    Ken, I'm definitely heavier. More fuel, 3 AGM batteries and a second power pole. I'm getting low 40's with mine. Since you know props, how does that Yamaha Talon compare to PT's SCD series?

    Leave a comment:


  • ken2
    replied
    Speed will be the question.
    The yamaha ran 50 MPH. 5 gal of fuel, they don't mention Trolling motor, and lithium ion batteries on a cool day with nothing in the boat.
    what speed are you getting with your Mercury?
    how are you loaded for your boat?

    Leave a comment:


  • Capt Jim
    replied
    My Merc has the 2.07 lower unit while the Yamaha has the 2.15 lower. I can't believe that would make that big of difference. I've spoken to Ken already; but, he really didn't have an answer and is also out of stock on props.

    Leave a comment:


  • Parker Yacht
    replied
    Originally posted by Capt Jim View Post
    Here's the Yamaha performance bulletin: https://yamahaoutboards.com/en-us/ho...115_3-7-18_flt Same hull as mine, engine is mounted in hole #2 and that motor is spinning a 20" prop to 6000 RPM while I can barely turn up an 18" to 5700. I have to think something is off here.
    I would check the gearing of the two lower units.
    The person to reach out to is Ken at Prop Gods.
    I'll move the thread.

    Leave a comment:


  • Capt Jim
    replied
    Here's the Yamaha performance bulletin: https://yamahaoutboards.com/en-us/ho...115_3-7-18_flt Same hull as mine, engine is mounted in hole #2 and that motor is spinning a 20" prop to 6000 RPM while I can barely turn up an 18" to 5700. I have to think something is off here.

    Leave a comment:


  • Parker Yacht
    replied
    Originally posted by Capt Jim View Post
    No jackplate; but, I'm going to have to confirm on the engine height. The Yammies I'm comparing it to are mounted in the second hole as mine. The other Merc boat I'd have to confirm.

    If I understand you correctly, a sticky anti siphon valve or other type of fuel line restriction, would not lower the fuel pressure. The lift pump or VST/FSM would supply the proper fuel pressure until it couldn't and then fall down. Not limit RPM, correct?

    Correct.


    Leave a comment:


  • Capt Jim
    replied
    No jackplate; but, I'm going to have to confirm on the engine height. The Yammies I'm comparing it to are mounted in the second hole as mine. The other Merc boat I'd have to confirm.

    If I understand you correctly, a sticky anti siphon valve or other type of fuel line restriction, would not lower the fuel pressure. The lift pump or VST/FSM would supply the proper fuel pressure until it couldn't and then fall down. Not limit RPM, correct?

    Leave a comment:


  • Parker Yacht
    replied
    Most fuel pressure's on Four Strokes these days stays constant. Meaning turn the key, pump comes on and 43#'s =/- is what you see. Idle or WOT.
    Now, things may change from idle to WOT on how long the pump comes on, but pressure should remain constant.
    I there is a restriction and the lift pump cannot supply the VST/FSM then it will fall on it's face, not stop at 5000 or 5700 rpm.
    Is your engine height the same?
    Jack plate?

    Leave a comment:

Working...
X