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Thread: Inboard Jet Boat Motor Question

  1. #1

    Default Inboard Jet Boat Motor Question

    I have a question about inboard jet boat motors. From my research, there are a lot of different makers and models of IB motors. If I were to purchase a jet boat, and down the road need to replace the motor, do most jet boats accept different kinds of motors? Or do certain boat makers build their boats to accept only certain makes of motors?

    For example, rather than putting in an expensive marine jet motor, could I put in something like a Chevy 350, fairly easy, or would that require a lot of changes and fabrication?

    The bottom line is, before I buy a jet boat, I want to know that I have options regarding motor replacement, rather than being limited to a particular engine maker.

    Thanks for your help!

  2. #2
    Member Dupont Spinner's Avatar
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    Most Jet boats now run a Chevy based block(no flames yet, read on), older models ran Fords and Chryslers. There is also some boats that have now incorporated an outboard powerhead for propulsion.

    There are differances between a marine engine and their automotive counterparts but all are internal. So the short answer to your question is yes it can be done. The problem lies in the materials the internal engine components are made of, especially in the valve area, and pistons. For example you would not want to use forged pistons in a marine block because most times you would not obtain block temps required to expand pistons to properly seal. Valves and valve springs would need to be changed to marine spec. Cams generally are low lift/shallow duration to save the valve train.

    A marine engine is made to run at a constant rpm for long periods of time. An auto engine runs at constantly differing rpms. I always think of a marine engine as if it is running uphill always.

    The good news is that a marine short or long block is not much more then a standard automotive block of the same type.

    If buying something look for something with fuel injection. Try to stay away from mulitple coil types.

  3. #3
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    You might want to join this Jet Boat forum:
    http://riverjetmagazine.com/fusetalk/forum/index.cfm

    These guys really know what they are talking about.
    Tennessee

  4. #4

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    Ultimately the pump and motor combo will drive the choice for your inboard. Beyond that most of the new motors are based on chevy offerings. I will say that from that point the motors deviate greatly. I compared Kodiak and Marine power engines and found that Kodiak marine did the best fit and finish. You can do some research on the riverjet forums and you will quickly avoid marine power modified engines. I have a Kodiak and things were done right with thier mods. I highly recommend the fuel injected option for gas savings and easy starts. Beyond that take a look at the pumps and recommended hp curves. If you have the cash get a hamilton pump and pair it with the right size motor for your application.

  5. #5

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    Thanks, everyone for your replies. There are so many motor choices out there, it's good to know that I have some choices regarding replacement.

  6. #6
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    As you read above the Kodiak motors are superior in every way. I have a 8.1 GM kodiak in my boat with a Hamilton 212 pump and its an awesome combination for a 22' and up boat. You wont be repalcing motors very often unless you run a commercial operation. Mahays in Talkeetna has some of these engines in the boats with upwards of 5000 hrs on them. Using proper maintenance techniques and synthetic oils they will last you and I a life time.

  7. #7

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    Quote Originally Posted by Arctic Mirage View Post
    As you read above the Kodiak motors are superior in every way. I have a 8.1 GM kodiak in my boat with a Hamilton 212 pump and its an awesome combination for a 22' and up boat. You wont be repalcing motors very often unless you run a commercial operation. Mahays in Talkeetna has some of these engines in the boats with upwards of 5000 hrs on them. Using proper maintenance techniques and synthetic oils they will last you and I a life time.
    Wow...5000 hrs. That's good to know. Those Kodiak motors do look nice. Any idea what they typically go for ($$$)?

  8. #8
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    I want to say around 10K for the 8.1 GM HO, the HO is the way to go in a river boat. The guy who built my boat can answer all your questions about prices and such, Artistic Aluminum Fabrication in Wasilla. (907) 229-8485.
    You can also check them out at KEM online.

    Are you re-powering a boat you already have? These 8.1 gm's get alot better fuel economy than the old ford 460 or the chevy 454. Not to mention they will last 4-5 times longer.

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