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  1. #1
    Registered
    My Boats:
    1995 Caravelle 20'
    Join Date
    Mar 2007
    Location
    Kansas City
    Posts
    38

    SBC Vortec heads - 062 or 906??

    Question - which casting number would be best for a mild SBC buildup? Why?

    I've heard the 062 flows just a tiny bit better than the 906, but the 906 has inconnel seats in them which I'm thinking might be better for a marine engine use...

    - the rest of the combo is a basic 355 with flat-tops (4 valve reliefs, -7cc), I'm re-using the XM262H cam/lifters, and was thinking of replacing the 'centerbolt' or "tbi" heads with some vortec castings and matching RPM Air-Gap intake.

    Also - how much HP do you guys think they're worth over the older (whatever is stock on a '95 5.7L non-magnum engine) with this setup? (Is it really worth the hassle of getting a set rebuilt and swapping intakes?)

  2. #2
    Registered
    Join Date
    Oct 2007
    Posts
    7
    I have posted a similar reply before, but I purchased the standard Vortec castings from Summit Racing not the ones with Iconel. I removed the stock heads from a 1990 / 91 Mercruiser 260. Kept the same pistions, installed the Vortecs, an Edelbrock Performer manifold, 1.5 roller Rockers, XM256 cam, Outer Z28 valve springs, new Mercruiser manifolds and risers. This is a heavy 3300+lb Wellcraft Eclipse 21 1/2 ft. Cuddy. Before mods, ran about 52.7 on GPS with a Mirage 21P. After mods turned a Mirage 23P at 5000 - 5100 rpm and 60.3 on GPS (a lot of propeller slip on this antique hull). So all these mods together picked up around 7 mph. I can only estimate that might be 300 propshaft HP from the previous 230 propshaft HP, but only a guess. There is a bit more in it with the right prop.

  3. #3
    Registered
    My Boats:
    checkmate 251 convincor,checkmate 253 convincor, 50 gibson
    Join Date
    Nov 2005
    Location
    Fredericksburg, Va
    Posts
    3,104
    either one will work fine...I would use the std performer and not the RPM on that app. Rob

  4. #4
    Registered
    My Boats:
    89 twin sbc 29 Fountain
    Join Date
    Jul 2001
    Location
    oshawa ontario
    Posts
    4,557
    I  Voted
    Quote Originally Posted by kornegle View Post
    I have posted a similar reply before, but I purchased the standard Vortec castings from Summit Racing not the ones with Iconel. I removed the stock heads from a 1990 / 91 Mercruiser 260. Kept the same pistions, installed the Vortecs, an Edelbrock Performer manifold, 1.5 roller Rockers, XM256 cam, Outer Z28 valve springs, new Mercruiser manifolds and risers. This is a heavy 3300+lb Wellcraft Eclipse 21 1/2 ft. Cuddy. Before mods, ran about 52.7 on GPS with a Mirage 21P. After mods turned a Mirage 23P at 5000 - 5100 rpm and 60.3 on GPS (a lot of propeller slip on this antique hull). So all these mods together picked up around 7 mph. I can only estimate that might be 300 propshaft HP from the previous 230 propshaft HP, but only a guess. There is a bit more in it with the right prop.
    nice gains!.......A Merc Revolution 4 would be a great prop for that boat

  5. #5
    Registered
    Join Date
    Oct 2007
    Posts
    7

    Wink

    I actually tried a labbed Revolution 4 in 23"P. Slippage decreased but not enough to compensate for rpm loss. I think it only turned about 4700 instead of 51 - 5200 and it was at least 1 mph slower but better midrange than the Mirage 23P. Ran a 25"P labbed Laser and it turned about 5000 rpm with similar speed to the Rev 4 but slipped bad coming onto the plane. Tried a stock 23P Mirage Plus and it was at least 1 mph slower than the 23P Mirage (because it turned around 200 rpm less). Put more cup in my old 23P Mirage, lost rpm and speed.
    I think I need to have my 23P Mirage labbed and I could probably pick up another 2 - 3 mph. Hardly worth it for an old boat like this (but in excellent condition).


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