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    Cummins 270 vs. 330 differences-gctid817856

    All I've been able to learn so far is that the 270 is fresh water cooled and the 330 is raw water cooled. I assume that means less maintenance costs on the 270, but are there other differences? In a 40 footer, is there a noticeable difference in cruise speed and fuel use? Any info greatly appreciated...
    Jeff & Tara (And Ginger too)
    Lake Havasu City, AZ
    |
    Current: 2008 Playcraft 2400 MCM 350 Mag B3
    2000 Bayliner 3388 Cummins 4bta 250s (SOLD 2020)
    2000 Bayliner 2858 MCM 7.4 MPI B3 (SOLD 2018)
    2007 Bayliner 305 MCM twin 350 Mag B3s (SOLD 2012)
    2008 Bayliner 289 MCM 350 Mag Sea Core B3 (SOLD 2009)
    And 12 others...
    In memory of Shadow, the best boat dog ever. Rest in peace, girl. 7-2-10

    #2
    We have the 270 hp motor and they are great. No raw water cooler to worry about. The shafts on the 330 hp are larger. We run around 1200 to 1500 rpm and we get great fuel mileage.

    Comment


      #3
      " In a 40 footer, is there a noticeable difference in cruise speed and fuel use?"

      I do not know which boat you are speaking about but the boat does not care which engines it has it juts needs a specific amount of hp to reach various speeds.

      So with that same amount of Hp at say 7 knots or say 15 knots these engines will consume the same amounts of fuel assuming they are correctly propped.

      With the Cummins 6B I am not a proponent of cruising at speeds that require burning about 9-10 gallons per hour per engine so that equates to about 200 hp each engine or less.

      Cruise with no more than about 2 cubic inches per hp extracted.

      Having more hp from that perspective will mean it will not affect the way I use the boat at all.
      Northport NY

      Comment


        #4
        All of thr Cummins engines use coolant and a heat exchanger as the cooling method.

        On the lower horsepower engines (approx 220 I think) the pressurized air goes from the turbocharger directly to the intake

        On the 270 horsepower version this air is first passed through a heat exchanger that uses engine coolant to reduct the air temperature, then the air goes to the intake manifold.

        On the 330 and 370 horsepower versions the heat exchanger for the air is cooled with seawater.

        This is because cooler air allows more fuel to be injected making more horsepower. The process of compressing the air in the turbocharger heats te air.

        KEVIN SANDERS
        4788 LISAS WAY - SEWARD ALASKA
        www.transferswitch4less.com

        Whats the weather like on our boat
        https://www.weatherlink.com/embeddab...59665f4e4/wide


        Where are we right now? https://maps.findmespot.com/s/36S4

        Comment


          #5
          Since the 270 has a water jacket cooled aftercooler you don't need to service the aftercooler on a regular basis. This is where the maintenance savings come in.

          As smitty mentioned, for a given speed, the fuel consumption of the two engines will be similar. But it will not be the same. If you look at the fuel curves of the 270 and 330 you will see that the 330 is a bit more efficient:

          https://www.google.com/url?sa=t&rct=...SL125SJDGEqGcw

          https://www.google.com/url?sa=t&rct=...BfwTXvzzh0X2Og

          For example, my boat has 270s. I cruise at 2200 RPM and get 15-16 knots. The 270 curve and tables show that it is producing 256 HP and consuming 8.5 GPH at 2200 RPM. The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH. In theory, the 330 is more efficient at the speed I like to cruise at. Also, at 2200 RPM it should cruise a bit faster, while consuming about the same amount of fuel as the 270.

          Personally I think some of the 330 advantage comes from having lower temperatures in the aftercooler, resulting in a denser air charge. Unfortunately, the Cummins tables do not show the aftercooler water intake temperature; so I assume it is the same as the air temperature in the test (77 F). The aftercooler water intake temperature on the 270 will be in the 200 F range.

          In practice you probably will see a bit of an improvement in fuel consumption or top speed with the 330.
          1999 3788, Cummins 270 "Freedom"
          2013 Boston Whaler 130 SS
          Anacortes, WA
          Isla Verde, PR

          Comment


            #6
            Jeff,

            One of my buddies had a 3988 with the 270's and that boat had plenty of power. I forget the maximum speed but IIRC it was around 20-21 kts. Another good friend just recently purchased the same 3988 but with the 330's. The top speed of his boat is 25-26 kts. Either boat will cruise all day long at 15 kts at roughly the same fuel burn ( same HP to make same speed) so the question becomes how often are you planning to cruse above 20 kts which would require the 330's. The guy with the 270's never complained about wanting/needing more HP. That said, there may be longevity issues to be realized with the 330's as you're extracting a lower percentage of power from the engine to make the same 15 kts compared to the 270's. This is probably a moot point for most owners as they run less than 100 hrs per year.

            Regarding the raw water cooling, in the 330's I believe the raw water only runs through the aftercooler then on to the heat exchanger where it then cools the engine coolant. The engine itself never "see's" the raw water, but you probably knew that.
            Jim Gandee
            1989 3888
            Hino 175's
            Fire Escape
            [email protected]
            Alamitos Bay, SoCal

            Comment


              #7
              I have 270's. Here's performance in my 3988 when new and probably a little lighter:

              Bayliner 3988 Cummins 270hp. Flat water, 2/3's fuel, full water, normal gear load.

              RPM SOG GPH MPG Range

              1000 7.1 kts. 3.00 2.37 639

              1100 7.9 kts 4.00 1.97 533

              1200 8.4 kts 4.80 1.75 472

              1300 8.7 kts 5.20 1.67 451

              1400 9.1 kts 5.80 1.57 423

              1500 9.5 kts 6.20 1.53 413

              1600 10.0kts 7.60 1.31 355

              1700 10.5kts 9.00 1.17 315

              1800 11.8kts 9.80 1.20 325

              1900 13.5kts 12.00 1.12 303

              2000 14.5kts 13.00 1.11 301

              2100 16.1kts 15.00 1.07 290

              2200 17.6kts 17.00 1.03 279

              2300 19.6kts 20.00 0.98 264

              2400 20.7kts 22.40 0.92 249

              2500 22.1kts 25.00 0.88 239

              2600 23.0kts 30.00 0.76 207
              1989 26' then 1994 32' now 2001 39'

              Comment


                #8
                "Norton Rider" post=817897 wrote:
                Since the 270 has a water jacket cooled aftercooler you don't need to service the aftercooler on a regular basis. This is where the maintenance savings come in.

                As smitty mentioned, for a given speed, the fuel consumption of the two engines will be similar. But it will not be the same. If you look at the fuel curves of the 270 and 330 you will see that the 330 is a bit more efficient:

                https://www.google.com/url?sa=t&rct=...SL125SJDGEqGcw

                https://www.google.com/url?sa=t&rct=...BfwTXvzzh0X2Og

                For example, my boat has 270s. I cruise at 2200 RPM and get 15-16 knots. The 270 curve and tables show that it is producing 256 HP and consuming 8.5 GPH at 2200 RPM. The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH. In theory, the 330 is more efficient at the speed I like to cruise at. Also, at 2200 RPM it should cruise a bit faster, while consuming about the same amount of fuel as the 270.

                Personally I think some of the 330 advantage comes from having lower temperatures in the aftercooler, resulting in a denser air charge. Unfortunately, the Cummins tables do not show the aftercooler water intake temperature; so I assume it is the same as the air temperature in the test (77 F). The aftercooler water intake temperature on the 270 will be in the 200 F range.

                In practice you probably will see a bit of an improvement in fuel consumption or top speed with the 330.
                The charts do not work anything like that - you would need a chart that shows fuel use in lbs per hp vs rpm to make that comparison.

                I may still have those charts around somewhere for the Cummins 6b I have not looked for them lately.

                If you could get this ...."The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH"

                Your would be producing 38.8 Hp / gallon of fuel at 7.0 lbs pre gallon. (260 / 6.7 = 38.8) That would be more than double what most modern diesels are able to achieve.

                In practice the 270 is pretty well tuned to reach best fuel burn in the 200 hp range if memoryy serves me well.
                Northport NY

                Comment


                  #9
                  "Jim Gandee" post=817898 wrote:
                  Jeff,

                  One of my buddies had a 3988 with the 270's and that boat had plenty of power. I forget the maximum speed but IIRC it was around 20-21 kts. Another good friend just recently purchased the same 3988 but with the 330's. The top speed of his boat is 25-26 kts. Either boat will cruise all day long at 15 kts at roughly the same fuel burn ( same HP to make same speed) so the question becomes how often are you planning to cruse above 20 kts which would require the 330's. The guy with the 270's never complained about wanting/needing more HP. That said, there may be longevity issues to be realized with the 330's as you're extracting a lower percentage of power from the engine to make the same 15 kts compared to the 270's. This is probably a moot point for most owners as they run less than 100 hrs per year.

                  Regarding the raw water cooling, in the 330's I believe the raw water only runs through the aftercooler then on to the heat exchanger where it then cools the engine coolant. The engine itself never "see's" the raw water, but you probably knew that.
                  "That said, there may be longevity issues to be realized with the 330's as you're extracting a lower percentage of power from the engine to make the same 15 kts compared to the 270's."

                  But you are extracting a higher oercentage or power form the same displacement of engine - I can fuel any engine up to a higher HP but that does not mean I have also put in place a safer working load just because I have raised overall hp.

                  At about 30 hp per liter of displacement these 6B's are very reliable and above that level you need to start becoming very aware of what is happening n real time.

                  5.9 x 30 = 177 hp
                  Northport NY

                  Comment


                    #10
                    "smitty477" post=817909 wrote:
                    "Norton Rider" post=817897 wrote:
                    Since the 270 has a water jacket cooled aftercooler you don't need to service the aftercooler on a regular basis. This is where the maintenance savings come in.

                    As smitty mentioned, for a given speed, the fuel consumption of the two engines will be similar. But it will not be the same. If you look at the fuel curves of the 270 and 330 you will see that the 330 is a bit more efficient:

                    https://www.google.com/url?sa=t&rct=...SL125SJDGEqGcw

                    https://www.google.com/url?sa=t&rct=...BfwTXvzzh0X2Og

                    For example, my boat has 270s. I cruise at 2200 RPM and get 15-16 knots. The 270 curve and tables show that it is producing 256 HP and consuming 8.5 GPH at 2200 RPM. The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH. In theory, the 330 is more efficient at the speed I like to cruise at. Also, at 2200 RPM it should cruise a bit faster, while consuming about the same amount of fuel as the 270.

                    Personally I think some of the 330 advantage comes from having lower temperatures in the aftercooler, resulting in a denser air charge. Unfortunately, the Cummins tables do not show the aftercooler water intake temperature; so I assume it is the same as the air temperature in the test (77 F). The aftercooler water intake temperature on the 270 will be in the 200 F range.

                    In practice you probably will see a bit of an improvement in fuel consumption or top speed with the 330.
                    The charts do not work anything like that - you would need a chart that shows fuel use in lbs per hp vs rpm to make that comparison.

                    I may still have those charts around somewhere for the Cummins 6b I have not looked for them lately.

                    If you could get this ...."The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH"

                    Your would be producing 38.8 Hp / gallon of fuel at 7.0 lbs pre gallon. (260 / 6.7 = 38.8) That would be more than double what most modern diesels are able to achieve.

                    In practice the 270 is pretty well tuned to reach best fuel burn in the 200 hp range if memoryy serves me well.
                    By no means did I want to imply that the fuel burn in the chart is what a boat will get. But the charts and curves are still valid for comparing the two engines. The 330 will develop more power at the same rpm and can be geared higher through the transmission and the prop. Thus it will be faster at the same engine rpm. Conversely t will burn a bit less at the same boat speed, with lower engine RPM.
                    1999 3788, Cummins 270 "Freedom"
                    2013 Boston Whaler 130 SS
                    Anacortes, WA
                    Isla Verde, PR

                    Comment


                      #11
                      "By no means did I want to imply that the fuel burn in the chart is what a boat will get. But the charts and curves are still valid for comparing the two engines. The 330 will develop more power at the same rpm and can be geared higher through the transmission and the prop. Thus it will be faster at the same engine rpm. Conversely t will burn a bit less at the same boat speed, with lower engine RPM"

                      The fuel burn, power output at various rpm will be a product of the transmissions and propeller chosen. In many cases the engines within a series that ultimately develops more power at higher rpm is not the one the develops power well at lower rpm. Do you happen to have the fuel use in pounds vs rpm curves available for these engines?

                      I have the Hino ones here but cannot find my old Cummins curves. The difference in the amount of HP derived by fuel weight (gallons) when you look across the full rpm spectrum of a Cummins is likely much more than you would expect.

                      " For example, my boat has 270s. I cruise at 2200 RPM and get 15-16 knots. The 270 curve and tables show that it is producing 256 HP and consuming 8.5 GPH at 2200 RPM. The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH. In theory, the 330 is more efficient at the speed I like to cruise at. Also, at 2200 RPM it should cruise a bit faster, while consuming about the same amount of fuel as the 270."

                      This is inaccurate and very misleading for folks that do not know about diesel engines.

                      "2100 16.1kts 15.00 1.07 290"

                      This one lien stolen from Uncle Bob sounds real good - about 15 gph total to reach 16 knots or about 277 hp being used between the two engines best case. (5 gph X 18.5 hp per gallon best case = 277Hp). So that means that Uncle Bob is extracting 139 hp per engine or about 50% of total available power (139/270). More importantly he is cruising at that speed utilizing 24 hp per liter of engine displacement (139 / 5.9 = 23.55).

                      All things being equal Uncle Bobs engines will see a long life. Than you Uncle Bob.
                      Northport NY

                      Comment


                        #12
                        "smitty477" post=817948 wrote:
                        "By no means did I want to imply that the fuel burn in the chart is what a boat will get. But the charts and curves are still valid for comparing the two engines. The 330 will develop more power at the same rpm and can be geared higher through the transmission and the prop. Thus it will be faster at the same engine rpm. Conversely t will burn a bit less at the same boat speed, with lower engine RPM"

                        The fuel burn, power output at various rpm will be a product of the transmissions and propeller chosen.

                        [color]blue wrote:
                        The engine power output at crankshaft has nothing to do with the transmission and propeller and that is the rated output that is on the curves [/color]

                        In many cases the engines within a series that ultimately develops more power at higher rpm is not the one the develops power well at lower rpm.

                        [color]blue wrote:
                        Agreed, but that is not what the output curves in this case show. Higher rated engines with forced air induction will often develop more power throughout the range than other engines in the same family.[/color]

                        Do you happen to have the fuel use in pounds vs rpm curves available for these engines?

                        [color]blue wrote:
                        It doesn't matter since both of the charts I shared use the same fuel parameters. See the note that starts with "Fuel Consumption" on the charts. So in this case a volumetric measurement of fuel is perfectly alright because the tests used the same parameters for the fuel in both cases. Remember we are doing a comparison between two engines under the same conditions.[/color]

                        I have the Hino ones here but cannot find my old Cummins curves. The difference in the amount of HP derived by fuel weight (gallons) when you look across the full rpm spectrum of a Cummins is likely much more than you would expect.

                        " For example, my boat has 270s. I cruise at 2200 RPM and get 15-16 knots. The 270 curve and tables show that it is producing 256 HP and consuming 8.5 GPH at 2200 RPM. The 330 curve shows similar horsepower (260) at 2000 RPM, with a resulting fuel flow of 6.7 GPH. In theory, the 330 is more efficient at the speed I like to cruise at. Also, at 2200 RPM it should cruise a bit faster, while consuming about the same amount of fuel as the 270."

                        This is inaccurate and very misleading for folks that do not know about diesel engines.

                        [color]blue wrote:
                        Physics dictate that a certain amount of power is needed to move a boat at a certain speed. In this case the 330 does in fact make more power at lower RPMs than a 270. With ideally matched transmissions and props and on the same boat, a 330 can achieve the same speed at lower RPM. [/color]

                        "2100 16.1kts 15.00 1.07 290"

                        This one lien stolen from Uncle Bob sounds real good - about 15 gph total to reach 16 knots or about 277 hp being used between the two engines best case. (5 gph X 18.5 hp per gallon best case = 277Hp). So that means that Uncle Bob is extracting 139 hp per engine or about 50% of total available power (139/270). More importantly he is cruising at that speed utilizing 24 hp per liter of engine displacement (139 / 5.9 = 23.55).

                        All things being equal Uncle Bobs engines will see a long life. Than you Uncle Bob.
                        [color]blue wrote:
                        I do agree with you that I misread the fuel curves. My thermo professor is probably turning in his grave. Incidentally, I do not have fuel flow meters, but I keep meticulous records of fuel usage. My numbers are a bit better than Uncle Bob's but my boat is a bit lighter - 3788 vs 3988. Also, my numbers include idling in and out of a marina.[/color]
                        1999 3788, Cummins 270 "Freedom"
                        2013 Boston Whaler 130 SS
                        Anacortes, WA
                        Isla Verde, PR

                        Comment


                          #13
                          Just to throw in a variable, my 1996 4087 has 270 B's with raw water aftercoolers. The 270's will plane the boat, but we spend most of our time at 7-9 knots. Turn on the autopilot, turn the dial once in awhile to course adjust, sit back and look out for logs.

                          Comment


                            #14
                            But you are extracting a higher oercentage or power form the same displacement of engine - I can fuel any engine up to a higher HP but that does not mean I have also put in place a safer working load just because I have raised overall hp.

                            At about 30 hp per liter of displacement these 6B's are very reliable and above that level you need to start becoming very aware of what is happening n real time.

                            5.9 x 30 = 177 hp
                            Smitty,

                            Great info and thoughts! I'm guessing one of the ways Cummins increases the HP from 270 to 330 is due to the increased intake air density thanks to the raw water cooled aftercoolers. The 330 engine enjoys a much cooler CDT (compressor discharge temp) air mass than the 270. All things being equal I'd take the 330's along with the larger transmissions and shafts that come with the package but if I found the perfect boat with 270's It wouldn't be a show stopper.
                            Jim Gandee
                            1989 3888
                            Hino 175's
                            Fire Escape
                            [email protected]
                            Alamitos Bay, SoCal

                            Comment


                              #15
                              I hesitate to wade in here, but the mechanical engineer in me compels me I think I can see where Norton Rider has gotten cross-threaded with Smitty, and it is partly to do with the confusing aspect of how Cummins has laid out its fuel curve graphs and tables. There is an upper and lower line on each graph. The upper line is basically the maximum power, torque and corresponding fuel flow (3 graphs) that the engine can produce at a given RPM. Assume you were in neutral and set your throttle to 2200RPM. Throttle is actually a misnomer as you are actually setting the engine governor to 2200 and fuel is adjusted to the load required to hold it there. Now assume that you had a variable pitch prop. At zero pitch, it would require just a little more fuel and hp compared to neutral. As you increased pitch, the hp and corresponding fuel required would go up with the pitch, assuming the governor is holding 2200 RPM. When you got to a pitch where the governor could no longer hold 2200 RPM, that represents the top line on the graph which is the maximum rated power for 2200 or any RPM on the curve.

                              The lower line represents a typical fixed propeller, including size and pitch, that Cummins has chosen to demonstrate the graph. This lower curve will vary with the pitch of the propeller. If you are over-pitched, this line will be higher and will end up intersecting the top line before you reach rated RPM (bad - see many posts by Smitty and others).

                              Anyway, the confusing part of the chart is that for the tables on the RHS, the first two show rated (maximum) and full load HP and torque (ie - the top line), but for fuel consumption, they show the typical prop curve numbers (the lower line), not the maximum rated consumption.

                              NR, your idea of measuring HP of your 270 at your cruise RPM of 2200, and matching it to the HP of the 330, and then comparing fuel flow is an excellent one. But the confusing aspect of the chart got in the way. If you expand those graphs and get out a ruler, and look at the 270 at 2200 RPM on the prop curve, it looks to me to show about 170hp, along with the 8.5 gal/hr consumption. Now if you work backward on the 330 curve starting at 170hp, it also shows pretty close to 2200 RPM (or maybe just a bit under), which is pretty close on the fuel consumption at 8.4gal per hour. That supports what Smitty was saying, that modern diesels should be pretty equal on the fuel they burn per HP output.

                              Also, in accordance with the above throttle/governor and variable pitch prop example, you can see that the engine power output at the crankshaft, as long as it is connected to a transmission and propeller, indeed does have everything to do with the transmission and propeller. In neutral (no pitch) it will require very little HP, but at max pitch it will require lots - the top line.

                              "Norton Rider" post=817980 wrote:
                              [color]blue wrote:
                              The engine power output at crankshaft has nothing to do with the transmission and propeller and that is the rated output that is on the curves [/color]

                              [/color]
                              Sorry for the long winded explanation :lol:
                              Mike
                              "Allante I" Rayburn 75
                              Previous: '97 4788

                              Comment

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