Max Running RPM'S

  • John Rasmussen
    Blaine
    Posts: 6328
    #1938135

    With the question about props from BoatsHateMe. I have a question about the rpm’s. I switched my prop to a stainless and bought it from Rapid Marine, there prop guy sold it to me and the first one I got I could peg the tach out easy, called him and he had me bring it back and exchange it for another he said would work. Well I love the new prop it jumps out of the hole and speed is good also. My question is I can still if trimmed up max out my tach (7000) I never run it quite that high, but what is ok or recommended? TIA

    Reef W
    Posts: 2712
    #1938141

    What is your motor? It should list a wide open throttle or maximum RPM range in the manual, 7000 sounds really high.

    John Rasmussen
    Blaine
    Posts: 6328
    #1938146

    Sorry it is a 2008 115hp Optimax Merc I bought it second hand. And I know I don’t want to run it at 7000 just wonder if 6500-6800 is ok or I need to get another prop.

    mwal
    Rosemount,MN
    Posts: 1050
    #1938147

    I have a 115 hp e-tec . They recommend 5500 to 6000 rpm. 7000 seems to high.

    Reef W
    Posts: 2712
    #1938149

    According to these it should be 5000-5700 max. I’m not sure if that manual is same as 2008 or not, all I could find, but it matches the rubex website. I don’t know how they could be so far off with the prop they gave you though… I’d be careful until you figure it out!

    https://www.rubexprops.com/boat-propellers/rpm-range/?make=Mercury

    http://download.brunswick-marine.com/filereader/file/pdf/4/enen/outboard/2006/optimax/10208r71.pdf

    The manual says to size the prop the WOT should be “upper half of the recommended full throttle RPM range.”

    John Rasmussen
    Blaine
    Posts: 6328
    #1938150

    Thanks I am also reading up on it, I’m finding 5700-6000 is desired so I guess I need to buy another prop.

    blackbay
    mn
    Posts: 870
    #1938151

    The max RPM on that outboard is 5000 to 5750. Your tach has to be off or you would have hit the rev limiter and had an alarm. Did you tell the dealership what RPM you were running? What prop and pitch are you running?

    John Rasmussen
    Blaine
    Posts: 6328
    #1938152

    I told him it was maxed out with the first one and never talked to him about the second cause it performed well and it only reaches that trimmed up. But it got me worried seeing others saying they run there’s at 5500. I am not sure on the pitch but I think it was a 17 or 18. If it matters the boat is a very deep v 17.5 feet. It is the Mercury upgrade vengeance I think.

    Rodwork
    Farmington, MN
    Posts: 3975
    #1938155

    Did the previous owner stroke the engine? That is high RPMs for that motor.

    MikeV
    Posts: 104
    #1938156

    Your tach is off. Get that solved first then work on props.

    B-man
    Posts: 5787
    #1938158

    Does your tach read 0 when the engine is off?

    Hot Runr Guy
    West Chicago, IL
    Posts: 1933
    #1938161

    5750 max. I suspect that your tach setting is off, since you haven’t said that the rev-limiter alarm has gone off.

    HRG

    Attachments:
    1. 2008-Opti-115.jpg

    hillhiker
    SE MN
    Posts: 1029
    #1938189

    Back of the tach there should be a small switch or dial for adjusting the pole setting. I believe the analog Merc gauges needed to be set to 4. This may help make your gauge read a bit more accurate.

    milemark_714
    Posts: 1285
    #1938239

    If you can’t spin,you won’t win.I would check tach settings as noted,and really would not want to overrev that motor.Shoot for the recommended RPM.

    buckybadger
    Upper Midwest
    Posts: 8131
    #1938245

    Same motor here and at WOT I’m at ~5400RPM. Engine has been great for me. I’d have to look to be completely confident what prop I’m currently running. The set-up pushes a 17′ Fiberglass Tuffy into the low 40s with 2 guys, a full tank of gas, and full livewell.

    marineman
    Posts: 105
    #1938262

    5750 max. I suspect that your tach setting is off, since you haven’t said that the rev-limiter alarm has gone off.

    I agree; an easy way to check is to see what the tach says when the engine is idling in neutral; should be between 600 and 800 RPM.

    John Rasmussen
    Blaine
    Posts: 6328
    #1938293

    Thanks for the help guy’s I looked at the prop last night it is an 18 pitch. I have never had it hit the revlimiter. I will have to look at the tach next time out to see what it reads at idle, can’t say I remember. I don’t know anything about the previous owner I bought it from a dealer after he traded it in. Had low hours and barely any use from what I could tell, so I’m guessing he did not modify it.

    John Rasmussen
    Blaine
    Posts: 6328
    #1938297

    I also looked at the original prop and it was an 19 pitch. Its been so long since I ran that one I don’t remember what rpms were. I guess I could through that one on and test it out.

    Bass Thumb
    Royalton, MN
    Posts: 1200
    #1938308

    I’d be extremely uncomfortable running any outboard over 5500 RPM. Mine is propped to max out at 5300.

    John Rasmussen
    Blaine
    Posts: 6328
    #1938315

    Is there a easy way to double check my tach is accurate? Other than what it reads off 0 like Bman said or 600-800 at idle as Marineman suggested.

    hillhiker
    SE MN
    Posts: 1029
    #1938323

    Is there a easy way to double check my tach is accurate? Other than what it reads off 0 like Bman said or 600-800 at idle as Marineman suggested.

    Find someone with a timing light with built in tach or talk to you dealer to see if they have a smartcraft gauge to borrow or have them verify with their diagnostic computer.

    I’d be extremely uncomfortable running any outboard over 5500 RPM. Mine is propped to max out at 5300.

    Careful with this mindset. I don’t know what you have for a outboard, but engine manufacturers set RPM ranges as high as they do for a reason. There’s bone stock outboards out there that are recommended to run in the 6800-7000 range. If you throw on an extra big prop to get RPM’s where you think they should be you can actually put more load on the engine than there should be, and in some cases even cause damage to the engine. That being said you don’t need to always run wide open, but the engine should be able to achieve the recommended wide open RPM’s with the prop you’re running.

    B-man
    Posts: 5787
    #1938371

    ^^^^^ Hillhiker is spot on, even if you don’t want to run it that high, you need it be able to.

    Lugging an outboard is a bad deal, and leads to premature failure.

    Beast
    Posts: 1121
    #1938526

    I agree your tach sounds like it’s off, 6000 rpms should be your max rpms, lugging a 2 stroke is worse than over revving.

    John Rasmussen
    Blaine
    Posts: 6328
    #1938580

    Thanks guys I guess I will be checking out my tach or taking it in for some more cash thrown at it.

    Hot Runr Guy
    West Chicago, IL
    Posts: 1933
    #1938594

    John,
    If this is a new to you rig, you might want to consider adding something like this SmartCraft System Monitor. Pulls data right from the OB, will give you rpms, hours, fuel used, water temp.

    This is a simple, plug & play install. The 20′ cable runs from a port under the cowl directly to the gauge. If I can do it, anybody can,,,

    https://www.ebay.com/itm/New-Mercury-Smartcraft-SC1000-System-Monitor-Kit-79-879896K21-w-20-Harness-/171532464384

    HRG

    Attachments:
    1. s-l1600.jpg

    John Rasmussen
    Blaine
    Posts: 6328
    #1938611

    Thanks HRG it is not really new to me, honestly I have had it for several years, added the new prop a couple ago. Everything has been fine, the rpm thing came up on another thread and made me worried. For nothing I hope? I will look into the smart gauges.

    Again thank you to all that chimed in, it is awesome to have help like this. Makes me glad to be part of a forum like this.

    Tight lines fellas!!

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