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Thread: BBC Identification

  1. #1
    CP Dad
    Need some help id'ing a BBC motor out of a boat I just bought. Seller said it was a crate marine Mark VI. Numbers on the block are 10237297, also found G187 near that mark on the rear lip of the bell housing boss. The heads show the numbers 14097088 and appear to be a closed chamber rectangular port. I popped the heads off to inspect the pistons and cylinders and they look very clean. Numbers on the pistons are 14097021. I didn't see any over bore marks (030, 060, etc), so I assume it's standard bore.
    I'm sure this has been covered before, but I need to know if I can use older Mark4 heads with this block. I have a fresh set of open chamber oval ports that will probably work better with the application I'm using it for (21 foot open bow with a jet and A imp). Is there a specific head gasket that I need to use?? Also, it has non adjustable rockers with 3/8 guideplates. Do the rocker bolts need to be torqued, or is tight good enough?? Thanks for the help............

  2. #2
    Jetaholic
    Off the Mortec site...
    10237297...454.......96-up...4-bolt, Vortec 7400", "L-29" Gen.VI
    I do believe you can run Mark IV heads on a Gen VI block...it's the Gen V blocks that can't run 'em. The main thing to check is to make sure the water jacket holes in the heads and the block match up. But I do believe Gen VI will accept Mark IV heads.

  3. #3
    IMPATIENT 1
    10237297...454.......96-up...4-bolt, Vortec 7400", "L-29" Gen.VI
    pretty sure the head bolt arrangement is different than a gen iv.

  4. #4
    obierno
    Your heads are rect open chamber 1991 up per #. The mark iv heads will not fit a stock gm mark v block due to water hole mismatch. bowtie and aftermarket block is a different story.I went thru this and was told that a special head gasket was made to solve the problem but I never found it. If your boat is fairly heavy you might consider the use ot the truck heads which provide better torque and will still work good at 5500 rpm. I have had great success in stock jet boats

  5. #5
    Jetaholic
    Actually, truck heads are better for lower RPM torque, which is useless with a jet since jets spin around 4500-5500RPM. The required hp/torque to spin the pump is all governed by the impeller size, not the weight of the boat. You would want a bigger impeller for more thrust at max RPM, as well as a motor that could spin it hard enough to achieve that RPM to generate the additional thrust to push a heavier boat. You would need heads that could make bigger torque at max RPM, and truck heads are not made for that.
    Basically, a heavier boat requires more thrust in the 4500-5500 RPM range to push it, which requires a bigger impeller (A, AA, etc etc), which requires more torque/hp from the engine to spin it in that RPM range.
    My motor has the 353049 heads and I'm making about 500ft lbs of torque at 4500 RPM. However, according to Chris Straub '049' heads are capable of making serious power, which means I'm probably leaving quite a bit of hp/torque on the table with my top end/cam combo.

  6. #6
    obierno
    My books list the truck (peanut) heads run out at 5000rpm and with a low end cam work great in a heavier boat, down grading to a smaller impeller is to be able to run in your power band due to the fact that your motor is probably built for higher rpm. so you gain 400 rpm down sizing . Smaller impeller in a heavier boat for family use does not have the low end with an average motor. I only suggested the option as a way to work with what he had. The thought of reworked 049 heads he might as well use the rect set he has. Only an opinion based on my ups and downs throwing money into boats.:idea:

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