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Thread: GM crate engines

  1. #1
    Does anyone know why I shouldn't put the 502/502 GM crate engine in my jet boat as is? GM says "not intended for marine use" is it corrosion they're worried about or something else?

  2. #2
    The cam that comes stock in that motor has some exhaust valve timing overlap. This could cause some water reversion through the exhaust into the combustion chamber.

  3. #3
    Wouldn't that happen with only a few types of exhaust & not all?

  4. #4
    Hey SP,
    I have a 502/502 in my boat. It's been in for 2 seasons and I haven't had any problems. I believe they say not for marine use due to the add ons-Non Marine carb, ignition and starter.The cam profile could be a little better to keep from having a reversion problem. I'm running water injected headers with a valve thus I haven't had that problem. I would suggest buying the long block version and adding your own ignition, carb. and starter. Also, if your concerned about the cam, change it. With a little head work, the right cam and carb, the 502 will make close to 575-600 hp and tons of torque....Bill

  5. #5
    Also you may have to change the oil pan like I did(may be to deep).

  6. #6
    I did almost this exact swap.Went from a 454 to the 450hs/502 it is the exact same longblock as the 415/502 mercruiser sells. I got one from Scoggins-Dickey few things I had to change: oil pan, intake manifold (if salt water cooled), starter, water pump, used flywheel off 454, had to switch to electric fuel pump, make sure head gaskets are composite or stainless and maybe a few other things but due to the 454 being a Mark IV. Don't know if the 502/502 has a different cam or not if so reversion might be a concern but can always buy the Stainless marine exhaust with long risers. Best Change I ever made, of course still not fast enough... eek!

  7. #7
    They just say that to keep from getting sued. The one guy is right about the cam, but if you run a manual shut off valve for the header water,and kill it at idle or run logs or lightning style headers, it won't be a problem.

  8. #8
    [QUOTE]Originally posted by SleekPanther:
    [QB]Does anyone know why I shouldn't put the 502/502 GM crate engine
    Every tech article I have read sez - cam will have risk of water "reversion" - be careful valve or motor damage could occur.

  9. #9
    I've heard some say that clearances for pistons, rings, bearings should be set different for a marine engine, usually wider. I'm OK with the reversion issue, it does have a fair amount of overlap in the cam. Open engine so I'm not worried about marine specific starter, ign and alt. I think I'm going to do it! Anyone interested in a tired 2 bolt 454 with 049 heads and tunnell ram with NOx? Cheap.
    Thanks to all those that responded,
    PS BBC502, what oil pan did you end up with?

  10. #10
    I'm just a little curious as to what makes their cam specs so different than a marine cam??? There are subtle differences right? But how would that create reversion as to a "marine" cam not making any???

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