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  1. #1

    Default looking for opinion on safe RPM operating range for Cummins 330 turbos

    Your opionions will be appreciated. I have twin 6bta 330 turbo Cummins, (5.9 liter) in my boat. Boat weight approx 32000lbs. The engines have 750 hrs and are in perfect operating conditon, no issues. For fuel economy I like to run them from 1650 to 1850 RPM and that pushes me along at 9 to 10 knots on my semi displacement hull. My boating buddies have warned me not to run the engines to long at the this low rpm range regularly*as it might damage the engines. (Glaze cylinders, carbon up etc...). at 2000 to 2200 RPM I can make 11.5 to 14 knots depending on conditions but my fuel consumption goes way up. Can I*safely run*at the lower 1650 to 1850 RPM range without*causing long term damage? The*engines seem to hardly*have to*work to maintain that range.

    Thank you for your consideration

  2. #2
    Join Date
    Jun 2008

    Default Re: looking for opinion on safe RPM operating range for Cummins 330 turbos

    Max cruise rpm's for that engine is ~2500 if I remember correctly. I would bring the engine up to at least 2300 - 2400 for 10 - 15 minutes each day if you are typically running at lower rpms. This will make sure that all the internal temps and loads are up to spec and help prevent any issues with glazing or similar.
    As for safely running them at 9 - 10knts (1650 - 1850), that will depend on your hull. Most hulls that would have a pair of these fitted are going to be in the 35ft - 45ft range. If you are in this range, 9 - 10knts is probably a 'bad' speed to be running your engines at. Hulls of these lengths will almost certainly be in the transition from displacement to planing, and 'riding the hump' like this may well be overloading your engines, eventually leading to incomplete combustion type issues. I run a 43ft launch with twin 5.9l 330hp Ivecos (very similar engine to yours) and once I get to ~8.5knts my next consistent speed is ~15knts where I am properly planing. I would only ever run between 8.5 and 15knts for short periods (maybe a few hours max) when the sea state requires it. Probably do less than 2% of my total engine time at these speeds.
    If your boat is comfortable at 9 - 10knts and that is the speed you would prefer to travel at, then I would compare your fuel burn at that speed with the fuel/hp charts for that engine to see if you are within the acceptable limits. If it is too high (as it may well be) then you should drop pitch off your props until you are within the designed fuel burn/hp for the rpms you are making at your cruise speed.
    I have ~4000hrs on my engines now and maybe 85% of that is at ~1200rpm, trolling at 8 - 8.5knts. I run my engines up to 2300 - 2500 at the end of every day (a day is usually 10 - 14 engine hrs) for at least 15 minutes, and more often 30 minutes. I also give them good long runs several times per season at 2300 - 2500rpm for 3 to 5 hours at a time. The engines have been as good as gold using this pattern, and I expect to see several 1000's more hours out of them yet. What I don't do however is run them at the transition speeds like you do as I feel this would kill them more quickly.

  3. #3

    Default Re: looking for opinion on safe RPM operating range for Cummins 330 turbos

    I have often, but not every time out, run them up to 2200-2400 for 10 minutes on my last leg of the day. I will pay more attention to that detail and make it a regular habit.

    Thank you Aliboy.

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