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Understanding Outboard vs. Inboard Engines

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  • Understanding Outboard vs. Inboard Engines

    This topic has been discussed multiple times before, but couldn't find any current or specific enough - so here goes...how do they compare in the following categories:

    ASSUMPTION! Comparisons are of boats in near-equal size, weight, usage, age, type; e.g., 1998-2002 18ft bowrider under 2,000lbs dry (no motor) for cruising & mild water sports.

    1) Fuel Economy: would a Merc. 3.0L 135hp I/O use less gas than a 2 stroke oil injected 90-115hp outboard? If not, are they about same consumption or is OB better?
    2) Power: would Merc. 3.0L 135hp I/O be of about equal speed & torque to 2 stroke oil injected outboard of 90-115hp? If not, are they same or is OB better?
    3) Noise: would Merc. 3.0L 135hp outboard be more quiet? Same or OB quieter?
    4) Longevity, maintenance, reliability, etc: how might they compare?
    5) Are there any technological changes that took place with 2stroke OBs that would change any of the above (fuel injection, etc., that would change any of the above - if so, roughly what years were those changes?
    Last edited by Rookster; March 25th, 2017, 02:38 PM.

  • #2
    1. No
    2. No
    3. Yes
    4. Depend on outboard and your skills
    5. The only 2-stroke motors left with efi are the E-tecs

    On an 18' boat, both motors would be underpowered, and the 3.0 would not be my choice for watersports
    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

    Comment


    • #3
      Originally posted by Scott Danforth View Post
      On an 18' boat, both motors would be underpowered, and the 3.0 would not be my choice for watersports
      Thanks - didn't know that about the Etecs!

      But hey...so is there a maximum boat length that you feel is appropriate for a 3.0L? And, is it really boat length that matters or is it really not weight? Or, is it both and why?

      Comment


      • #4
        the 3.0 is the entry level I/O motor. its a dinosaur as far as technology and hasnt changed much since its 1962 2.5 liter little brother. other than the longer stroke and it being made in mexico for the industrial division of GM (trash pump motors and marine motors) there is little difference than the 153 cubic inch motor designed 65 years ago

        the 3.0 uses more fuel than the 4.3, is somewhat loud (louder than a 4.3 or 5.0 although quieter than most 2-strokes) and is somewhat anemic on power.

        I had it in a 1650# (including motor and drive) boat that was just over 16' long. it got me to quite a few fishing spots, it pulled tubes ok (since your only doing 20mph), however pulling skiers required dropping pitch from 19 to 15 to get a proper hole shot and holding it against the throttle stops to keep the speed up if someone wanted to slalom. it wasn't a power house.

        If I was looking for a 18' boat, I would be looking for a 4.3 or 5.0 myself.
        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

        Comment


        • #5
          You would really want to have a 4.3L V6 sterndrive or a 150HPV6 outboard on a 18 footer. The 3.0 or 115HP OB would work, but not give great performance, IMO.

          That being said, if both motors have carbs, the sterndrive will use less fuel, but will have more, expensive maintence. It will also add about 1K pounds of weight to the boat, as it weighs in at 1100#. You may need a stronger tow vehicle for the I.O version of the boat.

          Now if you buy a modern Direct Injection Outboard and compare it to a new fuel injected sterndrive, the results will be different. IMO, the outboard will use less fuel, have less maintenance, and weigh much less than the sterndrive.

          Comment


          • #6
            HP to HP being equal, the OB will perform better due to less weight, on the order of 300-400 lbs or so. The OB will need less maintenance over time. The OB will be simpler and easier to winterize. The I/O will be cheaper to repower if you need an new engine at some point. It used to be that I/Os had a price advantage over OBs on new boats, because emissions caught up with 2 stroke outboards faster than it did with I/Os which were always 4 strokes. But now that I/Os must have EFI and cat converter exhaust the engine packages are comparable in price to OBs. So now you are seeing OBs on boats where you have not seen them for more than 20 years, like on the back of small to medium sport boats, not just fishing boats. I was just at the Nassau County Boat show in Long Island NY and we saw 2 mid size Sea Rays side by side, the I/O was slightly longer, the OB had about the same room and was actually cheaper.
            1988 Four Winns 200 Horizon
            4.3 OMC Cobra

            98 Jeep Grand Cherokee 4.0 Selectrac
            07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

            "While air doesn't freeze....rust never sleeps"

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            • #7
              Since the Merc 4.3 V6 is a more complex motor than the 3.0 I4, with more parts and hence more to break, all else being equal, wouldn't it logically be more expensive over time to repair?

              And a 4.3L sitting in a boat behind a bench seat/under a sunpad, isn't all that tougher to access than with a 3.0L?

              Comment


              • #8
                Originally posted by Rookster View Post
                Since the Merc 4.3 V6 is a more complex motor than the 3.0 I4, with more parts and hence more to break, all else being equal, wouldn't it logically be more expensive over time to repair?
                Only if you use in salt water since there is one more manifold.

                Oh yeah...and 2 more spark plugs and spark plug wires!
                1998 Wellcraft Eclipse 24 Cuddy
                Volvo Penta Duo-Prop 7.4L "LK"

                2006 Sun Tracker Party Barge 21
                Mercury 90 4-Stroke FI
                "Common sense is not very common"
                "Failing to prepare is preparing to fail." -- John Wooden

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                • #9
                  Originally posted by bruceb58 View Post
                  Only if you use in salt water since there is one more manifold.

                  Oh yeah...and 2 more spark plugs and spark plug wires!
                  Don't forget two more cylinders! Lol

                  Comment


                  • #10
                    Originally posted by Rookster View Post
                    Since the Merc 4.3 V6 is a more complex motor than the 3.0 I4, with more parts and hence more to break, all else being equal, wouldn't it logically be more expensive over time to repair?

                    And a 4.3L sitting in a boat behind a bench seat/under a sunpad, isn't all that tougher to access than with a 3.0L?

                    If the 4.3 was throttled back to the 3.0s top speed, it would be less strained and would be less prone to failure. As for access, a lot depends on how the boat manufacturer designs the stern of the boat. I have a V8 and it is quite accessible(full width sunpad), but I have seen some boats with the 3 liter where the access was very poor.
                    Last edited by jimmbo; March 25th, 2017, 08:31 PM. Reason: punctuation

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                    • #11
                      I have a 3.0 on a 17.5 foot boat. 15x17 prop. It pops right out of the water. I won't win many races but I can top out at 37 mph. Just my two cents.

                      Comment


                      • #12
                        Originally posted by Bigskyboat View Post
                        I have a 3.0 on a 17.5 foot boat. 15x17 prop. It pops right out of the water. I won't win many races but I can top out at 37 mph. Just my two cents.
                        Bigskyboat, what boat do you have - or what's the dry weight?

                        Comment


                        • #13
                          I'm not sure on the weight, it's a 1997 crestliner 1750 sportfish.

                          Comment


                          • #14
                            Originally posted by Rookster View Post

                            Don't forget two more cylinders! Lol
                            If you are concerned about when your engine finally needs to be replaced...there is ZERO difference new and will be way cheaper used to find a 4.3.

                            http://www.michiganmotorz.com/base-m...s-c-31_46.html

                            1998 Wellcraft Eclipse 24 Cuddy
                            Volvo Penta Duo-Prop 7.4L "LK"

                            2006 Sun Tracker Party Barge 21
                            Mercury 90 4-Stroke FI
                            "Common sense is not very common"
                            "Failing to prepare is preparing to fail." -- John Wooden

                            Comment


                            • #15
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                              Originally posted by Rookster View Post
                              Since the Merc 4.3 V6 is a more complex motor than the 3.0 I4, with more parts and hence more to break, all else being equal, wouldn't it logically be more expensive over time to repair?

                              And a 4.3L sitting in a boat behind a bench seat/under a sunpad, isn't all that tougher to access than with a 3.0L?
                              Actually since the 4.3 was used in millions of trucks, as well as thousands of gensets, trash pumps and a few million boats and the 3.0 is used in trash pumps, hydraulic power units and a few hundred thousand boats, its actually much cheaper to repair the 4.3

                              Rebuilding a 4.3 is about the same cost as a 3.0
                              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

                              Past Boats
                              1970 Wooster Hellion - Merc 9.8
                              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
                              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

                              What’s behind you doesn’t matter.Enzo Ferrari

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