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Cracked Block! / Mercruiser 305 to 350 Auto Conversion

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  • Cracked Block! / Mercruiser 305 to 350 Auto Conversion

    I know that this has been a topic of some discussion in the past, but I would like to ask more questions and get some fresh input on this subject. I am new to this list.I have a 1978 Reinell 6m with a Mercruiser 898 (305) with a cracked block. I can get my hands on a free 350 from an automobile. I don't know the specifics of the vehicle it came from yet. Does anyone know what differences I should be looking out for in the 350 versus the marine 305? I am planning to carry everything over from the 305 except the block, crank. Here's my initial list of things to take from the 305:Exhaust ManifoldsElectronic IgnitionPower Steering PumpFuel PumpThermostat Housing (with thermostat in it)Coolant PipingAlternatorStarterCarburator (add new jets?)Questions:Intake: Will the marine 305 intake fit on the 350? Should I swap it? Are they different? Mine is fairly rusty.Heads: Will the existing chevy 350 heads work ok in the marine application? Will the 305 heads work on the 350?Cams: If I use the 350's heads, can the 305 marine cam be moved over to the 350? I would imagine these to be very different given the change in displacementI am trying to do this with barely 0 investment overall. I already factored in gaskets ,fluids, and brass freeze plugs. What am I missing here?Thanks for all your help and sorry this is so long.Seattle Matt

  • #2
    Re: Cracked Block! / Mercruiser 305 to 350 Auto Conversion

    I would say you pretty much have it covered, except for the 305 heads, they are not suitable for the 350, just use the heads that are on the engine now. Also the cam in the auto 350 may not be good depending on where the engine came from. Too radical and you risk water inversion...The 305 cam would work in the 350 but I think you would need to replace the lifters.The 305 intake will work...The engine will need to be pre-1982 I think, anyway the dip stick should be on the port side of the engine.....
    The Devil to pay, and no pitch hot!


    • #3
      Re: Cracked Block! / Mercruiser 305 to 350 Auto Conversion

      If the 350 is 1987 to 1995, the intake from the 305 will not fit, same goes if the 350 is 1996 or newer, those have Vortec heads, If the 350 has dipstick tube on starboard side then its a 1987 to 1995, also need to check flywheel, it may be an issue, I just can't recall at this time, For the price of new cam and lifters, an RV cam will be close to a marine setup, but if the 350 is comimg out of a late 70's or early 80's type passenger car, its going to be dog, they only put out about 180 ponies, those were mostly low compression smogger motor's, I suggest you look on the front of the cylinder heads of the 350 and check what marks it has such a single hump or point or double bump etc. the markings will help determine if motor is high or low output and type of combustion chamber, any engine or speed shop will be able to tell you what the markings mean. The 350 been around along time, but had many different power variations over the years.... some strong some not.


      • #4
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        Re: Cracked Block! / Mercruiser 305 to 350 Auto Conversion

        Here is a very good article on the differences between a marine and auto motor.