Cam Selection 350 Mag ' 87

Discussion in 'Gas Engines' started by DTM, Jun 14, 2011.

  1. DTM
    Joined: Jun 2011
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Atlanta, GA

    DTM New Member

    Am in the process of building an '87 350 Magnum (to replace a freeze damaged heads and block) in a Donzi Z21. In the process of selecting a cam and am looking for some input (I am a "car guy" and not sure about a cam selection for a boat with "wet" exhaust).

    The engine is basically a stock 2 bolt 350 (non-roller block) and the heads are 882's. The exhaust is straight through the transom and there is a Q-jet on the stock manifold. I am running a Alpha drive with a Power Tech 19P. The boat use to max at ~4,800 RPM with the stock (260HP). Looking to increase to ~300HP.

    I was wondering what were the specs on the original cam and what cam would be a good fit with these heads? Do not mind a "little" lump in the idle. Planning on staying with the tappets as a roller is too much $$$ for the build and what I think the return would be.

    Thoughts?
     
  2. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Stick with a standard cam and 260HP or less. That already drives the Alpha to its physical limits.
    With more torque the vertical drive shaft snaps where the upper O-ring groove is. It may not happen straightaway on your 1th trip when you stay near the marina and treat the engine gently because you just assembled it.
    The usual place for this to happen is far away and the only people you can see are those in your boat.
     
  3. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The original camshafts were made by Crane. They are readily available.
     
  4. DTM
    Joined: Jun 2011
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Atlanta, GA

    DTM New Member

    Original Cam Specs

    Does anyone know the original cam specs for the '87 350 Mag (Carb)?
     
  5. powerabout
    Joined: Nov 2007
    Posts: 2,913
    Likes: 62, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    yes but Crane will not sell them to you( last time I checked),you will need to go to Merc.
    There are other cams Crane/Merc made for 350's and they were used in the 280,300 and 320 no problem at idle but a little better if your boat does over say 55mph
    These will lift the peak torque and hp up the range a bit. With these there is no other change required in the valve train so its a simple install.
    Personally I would install roller tip rockers ( cheaper than full rollers) and guide plates and screw in studs for sure.
    Edelbrok also made the inlet manifold for the merc 280 and 300( which they will sell) it is anodised black so it will survive in sea water.
    If you want to run WOT all day you will also need an oil cooler.
     
    1 person likes this.

  6. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The Mercury number is 431-5943 and the Sierra number is 18-1484. It is the same from the 228GM to the 350GM Magnum and the 5.7 Ski
     
    1 person likes this.
Loading...
Similar Threads
  1. Art1848
    Replies:
    3
    Views:
    4,381
  2. kobus
    Replies:
    12
    Views:
    3,784
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.