Block compatibility IV vs VI
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Block compatibility IV vs VI

  1. #1
    Custom user title Big Inch's Avatar
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    Default Block compatibility IV vs VI

    So I need a new block and rotating assembly. Original is a Gen VI. What the pros and cons between Mark IV and Gen VI and compatibility of parts?

    What I know, or think I know, is that the Mark IV is higher nickel content so stronger. Is that a big consideration on a pump gas N/A deal spinning less then 6k rpms.

    Compatibility of parts.
    VI heads can go on a IV block but not vice versa?
    Oil pan is different I believe
    No mechanical fuel pump on VI but I have the belt driven fuel pump from the original motor.
    Will my Gen VI flywheel be ok with a Mark IV block.
    Not planning on using the stock balancer.
    Anything else not compatible?

    Thanks in advance

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    Senior Member Boat 405's Avatar
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    Quote Originally Posted by Big Inch View Post
    So I need a new block and rotating assembly. Original is a Gen VI. What the pros and cons between Mark IV and Gen VI and compatibility of parts?

    What I know, or think I know, is that the Mark IV is higher nickel content so stronger. Is that a big consideration on a pump gas N/A deal spinning less then 6k rpms. No problem. I have a gen VI putting out around 740hp no problems, also have run a 150hp shot of nos on top of that.

    Compatibility of parts.
    VI heads can go on a IV block but not vice versa? Yes and no, heads are interchangeable with correct head gasket
    Oil pan is different I believeYes
    No mechanical fuel pump on VI but I have the belt driven fuel pump from the original motor.no problem if running a belt driven pump
    Will my Gen VI flywheel be ok with a Mark IV block.maybe depending on the balance (external or internal)
    Not planning on using the stock balancer.again depends on balance
    Anything else not compatible?timing covers

    Thanks in advance
    just about everything else is the same, oiling routing is different internally. priority mains. if you have specific questions about running oil coolers and remote filters send me a PM
    Boat 405.

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    gn7
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    Quote Originally Posted by Big Inch View Post
    So I need a new block and rotating assembly. Original is a Gen VI. What the pros and cons between Mark IV and Gen VI and compatibility of parts?

    What I know, or think I know, is that the Mark IV is higher nickel content so stronger. Is that a big consideration on a pump gas N/A deal spinning less then 6k rpms.

    Compatibility of parts.
    VI heads can go on a IV block but not vice versa?
    Oil pan is different I believe
    No mechanical fuel pump on VI but I have the belt driven fuel pump from the original motor.
    Will my Gen VI flywheel be ok with a Mark IV block.
    Not planning on using the stock balancer.
    Anything else not compatible?

    Thanks in advance
    Mark IV heads can be used on a GEN VI. The problem is with the GEN V block.
    Oil pan is different
    There is a fuel pump boss on the GEN 6 454 and service replacement blocks
    The Gen VI flywheel fits but is balanced defferent than Mark IVs. Gen VI uses 2 differenflywheels. One for forged cranks, and one for cast cranks. Have the Gen VI balanced to Mark IV specs (or better yet, have the whole assembly rebalanced including the flywheel)
    Front balancer is compatible, but the check the placement of the timing marks. Many Gen GVs have no timing marks.
    Stock GM oil pump will hit the main cap bolts, newer after market pumps will. Replace it anyway.



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    Quote Originally Posted by gn7 View Post
    Mark IV heads can be used on a GEN VI. The problem is with the GEN V block.
    Oil pan is different
    There is a fuel pump boss on the GEN 6 454 and service replacement blocks Mine doesn't have one am I mistaken about it being Gen 6?
    The Gen VI flywheel fits but is balanced defferent than Mark IVs. Gen VI uses 2 differenflywheels. One for forged cranks, and one for cast cranks. Have the Gen VI balanced to Mark IV specs (or better yet, have the whole assembly rebalanced including the flywheel) Roger that
    Front balancer is compatible, but the check the placement of the timing marks. Many Gen GVs have no timing marks. Is that balancer suitable on a mild performance deal or will it make one of those ultra cool water letter outer holes in the bottom of the boat?
    Stock GM oil pump will hit the main cap bolts, newer after market pumps will. Replace it anyway. Gotcha
    Thanks

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    No, you aren't confused because you have no fuel pump boss. Gen V/VI from Merc have none. If its a roller lifter motor, is a 6. If not, its a 5. Also, the 4 and 5 have a different timing cover from the 6. The 6 has only 6 bolts

    If its a Gen 6, your lifters won't work on a Mark IV.

    99% of the engines we do use aftermarket heads which are based on Mark IV heads. As was said, there are gaskets out there that are supposed to make Gen 6 heads work on Mark IV blocks, but I have heard cases where they have created issues.

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    gn7
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    User is correct. Mercs do not have fuel pump bosses. But I am lead to believe you are buying a GEN 6. Service blocks are suppose to have a boss. Roller lifters are different in the 6, and STOCK 6 heads can be problematic on a IV block, but IV heads will work on 6's block, they don't have the funky big azz holes the 5's do, and yes you will need a different T cover.



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    Quote Originally Posted by gn7 View Post
    User is correct. Mercs do not have fuel pump bosses. But I am lead to believe you are buying a GEN 6. Service blocks are suppose to have a boss. Roller lifters are different in the 6, and STOCK 6 heads can be problematic on a IV block, but IV heads will work on 6's block, they don't have the funky big azz holes the 5's do, and yes you will need a different T cover.
    The stock block is a Gen 5. When I ran the numbers it was in the boat so maybe I didn't read them well but it has 10 bolts on the timing cover, not hydraulic roller, and now that I can clearly see the numbers mortec says its a Gen 5.

    So is the Gen 5 pan and flywheel the same as Gen 6? Should I stay away from a Gen 5 block? I apparently can get a really good deal on a new Gen 5 block but sounds like it's kind of a bastard deal and maybe I should stay away from it?

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    Quote Originally Posted by Big Inch View Post
    So I need a new block and rotating assembly. Original is a Gen VI. What the pros and cons between Mark IV and Gen VI and compatibility of parts?

    What I know, or think I know, is that the Mark IV is higher nickel content so stronger. Is that a big consideration on a pump gas N/A deal spinning less then 6k rpms.

    Compatibility of parts.
    VI heads can go on a IV block but not vice versa?
    Oil pan is different I believe
    No mechanical fuel pump on VI but I have the belt driven fuel pump from the original motor.
    Will my Gen VI flywheel be ok with a Mark IV block.
    Not planning on using the stock balancer.
    Anything else not compatible?

    Thanks in advance
    AM I wrong or ??,,,,, are you trying to put gen 6 part's on a new mark IV aftermarket block ??........................E

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    Quote Originally Posted by Big Inch View Post
    The stock block is a Gen 5. When I ran the numbers it was in the boat so maybe I didn't read them well but it has 10 bolts on the timing cover, not hydraulic roller, and now that I can clearly see the numbers mortec says its a Gen 5.

    So is the Gen 5 pan and flywheel the same as Gen 6? Should I stay away from a Gen 5 block? I apparently can get a really good deal on a new Gen 5 block but sounds like it's kind of a bastard deal and maybe I should stay away from it?
    Gen 5 has 10 bolts. Gen 6 has 6

    5 and 6 use the same pan (1 piece rear main seal)

    Gen 5 was only around for 5 years. Most people hated it because even Mark 4 heads could be an issue on it.

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    Quote Originally Posted by alkyexpress View Post
    AM I wrong or ??,,,,, are you trying to put gen 6 part's on a new mark IV aftermarket block ??........................E
    Just a new to me block. Trying to figure out if I should get a mark 4 or gen 6 block and go from there. The parts I would reuse if I get a gen 6 block would be the pan, flywheel, and belt driven fuel pump.

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    Quote Originally Posted by 5325user View Post
    Gen 5 has 10 bolts. Gen 6 has 6

    5 and 6 use the same pan (1 piece rear main seal)

    Gen 5 was only around for 5 years. Most people hated it because even Mark 4 heads could be an issue on it.
    So stay away from Gen 5 then hehe.

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    Quote Originally Posted by Big Inch View Post
    So stay away from Gen 5 then hehe.

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    gen 5 is the red headed step child of the bunch.
    Boat 405.

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    I really dig the gen six's. They are all four bolt mains, have priority main oiling, blind head bolt holes and I feel like they are a stouter deal than the IV's. I also like the rear seal better. Some lifters sold for the mark IV's will fit, but the lifter bore is .300 taller. My crane mark IV lifters fit with about .050 clearance. The timing chains suck as do the timing pointers as they are part of the timing cover. The only timing cover's that I know of that will fit a double roller chain are the one sold by cp performance and milodon makes one. The roll master chain is nice and will fit behind the stock cover. The cam is held in using a bolt on cover to control the thrust but other than the register cut in the front of the cam the cams are the same. Hey Widow that system one deal on your 21' is bitchen! I would also stay away from the V's. SJ

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