help me decide...complete rebuild or head swap
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help me decide...complete rebuild or head swap

  1. #1
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    Default help me decide...complete rebuild or head swap

    my 1995 ultra jet boat came with the 340hp gen v 454 with peanut port heads, 4 bolt, forged crank/rods, cast pistons. last time i took it out was about 18 months ago and got some signs of a blown head gasket, didnt really look much into it...just wrote it off as a good reason to get more power. still great oil pressure, held 5000rpm the last 15 seconds before i trailered it, only 80 hours on engine. Im in the coast guard, been gone a lot of the last 18 months, just recently picked up a gen IV 454 that was previously in a jet boat that "crashed". the guys story was flawed, in the end i have a 2 bolt w/ cast crank and forged pistons that needs to be rebuilt. but it did come with fresh 702 heads that just need a little work and they are good to go....and and an entire new comp cams valvetrain...covered in rust

    So should i just take the 702 heads and transfer them over to my gen V? or ditch the gen V and rebuild the gen IV? ive read the coolant passage ways can be a bitch with gen V block/ gen IV heads and i need the right head gasket, but it would boost my compression and flow better. I would keep the stock cam/lifters for now and see if i need a different length push rod.

    right now my only concern is getting back on the water this spring before my job sends me away all summer.

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  3. #2
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    How much $$$ are you looking to spend and desired results?

  4. #3
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    Check out the response on this forum. Pretty good information on a lot of BBC heads. May help you make up your mind. The one thing I did see was the head change if I read the information correctly would result in about a 25% increase in compression ratio if you use the same pistons. If you are starting at 9.5:1 you end up at almost 12:1. No more pump gas for you. Are there's heads worth a damn? [Archive] - Chevelle Tech

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  6. #4
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    The stock compression on the gen 5 is 8 to 1, so if I were to put the 702 heads it would be around 9.8 to 1 depending on head gasket. 91 octane should be fine. I can spend 2 grand, would rather not though. The heads were rebuilt right before they were left outside for a year. Seats and guides should be good, springs and valves and rockers will need replacing. I'm reading the link you posted, lots of information. I'm trying to find out if head height is different resulting in push rod length issues. Thank you for your help.

  7. #5
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    Default Gen 5 to 4...

    Quote Originally Posted by nos1967 View Post
    The stock compression on the gen 5 is 8 to 1, so if I were to put the 702 heads it would be around 9.8 to 1 depending on head gasket. 91 octane should be fine. I can spend 2 grand, would rather not though. The heads were rebuilt right before they were left outside for a year. Seats and guides should be good, springs and valves and rockers will need replacing. I'm reading the link you posted, lots of information. I'm trying to find out if head height is different resulting in push rod length issues. Thank you for your help.
    From my limited experience with the gen V I seem to remember the push rods being different. As well as the rockers, and maybe even the lifters.... The Felpro 1037 head gasket is suppose to work on all the different generations under a 4.340 bore.....

    There are others here that do these inter generational swaps all the time, maybe one of them will join in the conversation....

    Ray
    LOUD BOATS SAVE LIVES

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