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Volvo penta aq211 swapping 1pc to 2 pc rear main seal block

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  • #16
    Originally posted by Scott Danforth View Post
    yet for some reason both Mercruiser and Volvo increased timing from 8 degrees BTDC to 10 degrees BTDC with the vortec heads (while still running the junk flat-top 4-relief pistons from GM) to help get the power from the motors that the vortec heads help extract.

    Engine temp has more to do with timing than any amount of quench, even with properly built vortec motors with d-shapped (LCQ style) pistons.
    All the engines I've seen with vortec heads use dished pistons with reduced compression. There is no quench. Initial timing has no bearing on total timing without knowing what is in the specific advance module used.

    D shaped pistons are the way to go, but you must have a zero deck height for the standard 0.038" gasket crush thickness (non-marine) to be effective.

    Cylinder head temps affects auto - ignition more than timing. So do sharp edges and excessive carbon deposits. This is why many engines "run-on". No matter what the head temp, the fuel charge should burn at a finite rate, not spontaneously combust. Frankly, this is what octane does..determines resistance to compression ignition.

    Bore diameter affects total timing also. That's why a "mag drop" works on an aircraft..those dam pistons must 5-6" across. Flame front is ignited from 2 directions. Drop one mag, the flame front has to spread from one side only. Less pressure build-up, less power. Actually, since aircraft timing is stationary, if the mags are too far advanced, there is no mag drop.

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    • #17
      Dropped off my saw to the race shop and got some specs off of the cam

      Duration 278/288, Lift .420/.433,

      Its a flat tappet cam that they run on roller motors with roller lifters. I guess they liked the performance of them, from what the old dude who used to build their motors said they used them as a loop hole cam to get by some cam size regulations at the circle track and tried them on street cars with lots of success (their cost on them is about 35 bucks a cam so I'm sure that helps too).

      not sure I'm digging that set up, not for a boat anyway. The power range is from about 1200 to 4800 rpms. Moves higher with advanced timing which i wont be doing.

      These guys dont build boat motors, don't really build car motors either now that all the local guys have gone to crate motors on the circle track. They used to build for and race against the Earnhardt family (Dale Sr would have been a kid back then) no doubt the old guy knows his stuff but im not sure how much of the newer technology has past them by. Anyway, im thinking cam change but wanted to get your opinion


      its a melling mc-1 cam

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      • #18
        The Melling MTC-1 cam is a good street cam for a car, NOT a marine cam. too much overlap to be used in a boat with wet exhaust

        get a marine cam. 268 degrees of duration on a flat tappet is max. 270 on roller is max.

        suggest one of the following for a flat tappet

        either the CL12-236-3 - Comp Cams 'Xtreme Marine' Hydraulic Flat Tappet

        Operating Range: 1300-5500 RPM
        Duration Advertised: 262 Intake / 268 Exhaust
        Duration @ .050'' Lift: 218 Intake / 224 Exhaust
        Valve Lift w/1.5 Rockers: .462'' Intake / .477'' Exhaust
        Lobe Separation Angle: 112

        or the CL12-232-3 - Comp Cams 'Xtreme Marine' Hydraulic Flat Tappet

        Operating Range: 1300-5000 RPM
        Duration Advertised: 256 Intake / 262 Exhaust
        Duration @ .050'' Lift: 212 Intake / 218 Exhaust
        Valve Lift w/1.5 Rockers: .447'' Intake / .462'' Exhaust
        Lobe Separation Angle: 112
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

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        • #19
          You mean they run roller lifters on a flat tappet cam? You can't do that. One is steel, one is iron.

          RETARDING cam timing slightly moves the power band up.

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          • #20
            So ive got my new transom seal strip on its way. I already have 4200 to glue the ends together and contact cement to hold the ring in place. How about added sealer between the seal strip and the transom? Looks like the factory used silicone.

            should i use 4200? Life calk? Any suggestions?

            Also i have some corrosion on the transom shield around the outter doughnut gasket. I've cleaned it up well but would like to add a sealer there too...again open to suggestion

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            • #21
              shouldnt need anything between the seal and the transom. not even silly-cone

              blast and paint the transom shield
              Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

              Past Boats
              1970 Wooster Hellion - Merc 9.8
              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

              What’s behind you doesn’t matter.Enzo Ferrari

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              • #22
                I did blast and paint but there are imperfections on the shield from corrosion in a few spots.



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                • #23
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                  You can't compare roller cam specs and flat tappet specs directly. Roller lifters contact the cam at one narrow spot. Flat tappet specs are affected by the whole lifter face (3/4" or so) contacting the lobe as the lobe rotates. The wider the lifter face, the longer the duration. Peak lift is the same with both styles. The centerline of the flat tappet lifter is offset from the centerline of the cam lobe..this allows the lifter to spin in it's bore and wear more evenly.

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