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  1. #1
    Seaman Apprentice
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    Default Recommended safe cruising revs for Mercruiser 350's

    Firstly I should say I'm new to these threads and have found them to be an astounding information resorce. Thank you all for the contributions.I run a pair of 350's in an older Searay. I'm wondering about a safe high end (revs) for an extended cruise of 4 or more hours. My concern is more about long term life of the engine. The Searay specs suggest that I prop my boat to allow a WOT of 4200.

  2. #2
    DJ
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    WOT at 4200 is good. Cruise around 3000.

  3. #3
    Captain
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    It really depends on the size props you are running with.A smaller prop which will make it a little tougher to get up on plane will take higher rpms to cruise but will be easier on your motor.If you have larger props and you jump up on plane right away and can pull a water skiier up right away,this will require less rpms to cruise but will in time stress your engines life.3000 rpms sound reasonable for easy cruising as long as you take the prop size into consideration. Charlie

  4. #4
    Petty Officer 1st Class
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    Marine 350 GM's should take 4200 rpm's all day. If the boat's been re-powered and not with Marine engines, then all bets are off. The newer Vortec's are rated at 4800 continuous. Your crusing speed is a function of the boat, engines, need for speed and fuel efficiency. Unless range and fuel consumption are no issue, you won't be at 4200 very long.

  5. #5
    Seaman Apprentice
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    Thank you all. I think I needed reassurance that a lengthy run in the 3200-3500 range isn't a bad thing for my engines. It's a relatively heavy boat and with a full load of water and fuel it requires 3300+ for a good solid plane. It was correctly noted that both range and fuel consumption are adversly affected.

  6. #6
    Moderator Bondo's Avatar
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    Total Engine Life, Will be Much Shorter at 4200rpms - Vs - 3500rpms......WOT is Not for All Day Running....
    Any Grease is Better,..... Than No Grease at All.......

  7. #7
    Seaman Apprentice
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    Bondo. How do you feel about working 350's at 3500 on a regular basis. I'm propped to dealer specs. Incidently I tend to run mostly at a fast idle 1500 gives me 7 knots and allows me to enjoy the scenery. 3400 is for getting home in a hurry or crossing a long and boring expanse.

  8. #8
    Moderator Bondo's Avatar
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    A Properly Maintained SBC will Pull at 3500rpms for atleast 5,000hrs......At 4500rpms that'll drop to Maybe 1/2....At 1500rpms..... It'll Last Forever.....
    Any Grease is Better,..... Than No Grease at All.......

  9. #9
    Commander magster65's Avatar
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    My thoughts are you shouldn't run a gas engine at more than 75% of it's maximum rpm for extended periods. So 4200 rpm x .75 = 3315 rpm.
    Arrr matey!
    2002 3788 Bayliner "Motley Crew"
    Twin 270 Cummins

  10. #10
    Petty Officer 1st Class
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    Run where you need to to get a good clean plane. If your boat is plowing at 3200 and planing at 3500 then the higher revs will be easier on everything. I've run 100's of hours on my Chrysler 400's at low revs but occasionally they really like to be opened up for an hour or so or the idle gets unstable. Spent a bunch of time trying to tune it out and came back from a hard run and noticed it had fixed itself.

  11. #11
    Lieutenant Commander flashback's Avatar
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    I have a 350 in a 21ft deep V and find that it runs all day at 2100 to 2500 Rpm. anything less and it struggles to stay on plane, anything more and the other 2 barrels start cutting in and then fuel consumtion goes to hell...........
    The Devil to pay, and no pitch hot!

  12. #12
    Seaman Apprentice
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    Default Re: Recommended safe cruising revs for Mercruiser 350's

    Yes I get less than a mile per gallon opened up, almost double that if I keep the revs down and am content to putt along. Expensive, but we have some of the best cruising on the planet, so it's worth it.

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