4.375
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4.375

  1. #1
    Senior Member Meaddaytonamike25's Avatar
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    Default 4.375 question

    I want to build a blown bbc with a goal of 1000hp on 91 pump gas. I have been considering a 4.375 stroke but I'm worried that this stroke will move the upper ring to high for a blown application. I will be using a std 9.8 bow tie block. Anyone have any experience with a similar build.
    Last edited by Meaddaytonamike25; 09-22-2012 at 08:51 AM.

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  3. #2
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    A blown 540 with a 4.250 stroke will make 1000 on pump gas blown

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    Senior Member racinjason65's Avatar
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    I've got a 565 9.8 deck with 4.25 stroke 4.6 bore. It makes 1050 hp 1020 tq.

    If you are looking for more displacement, I'd start looking at tall deck blocks. If 1,000 hp is your goal and you've already got the block, build a 540 or a 565.

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  6. #4
    Senior Member Meaddaytonamike25's Avatar
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    Is there an advantage the 4.25 stroke has over a 4.375? If I'm starting from scratch why wouldn't I want the larger stroke?

  7. #5
    gn7
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    Because as you said the pin gets higher on the piston. The ring pack is moved up, and tighter together, and the pin gets closer to the deck of the piston. All not the best arrangement for a blown engine. If it was a N/A deal no real issues. Not my favorite combo by along shot, but at least acceptable. In a blown deal, not so much.

    I'm not even a huge fan of blown short deck 496 with a 6.385 rod, but they will work. The ring pack is still within reason. I perfer my top ring further down than you can accomplish with a 4.25 crank and a 6.385 rod.

    Interesting that when Mercury built there 1350 HP pump gas quad cam 4 valve twin turbo'd 540 they used a tall deck.
    When GM built the 4.375 stock 8.1/496 they used a tall deck.



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  8. #6
    Senior Member EVILFORCE's Avatar
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    I have built a lot of 557's tall decks using a 4.375 crank. I use a 6.405 rod. I have one now sitting on the engine stand. It is a lot easier to get parts for a 4.250 stroke. Like Bob said. You can get into piston issues. The one I have now has custom Ross pistons. That is the only way to get the ring pack down. This was built with the intention of being blown but that project had been scrapped. Stick with the off the shelf stuff. It will save you a bunch
    No Fool Like A Old Fool is there?

  9. #7
    Senior Member Meaddaytonamike25's Avatar
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    Thanks for the input guys. I guess I'll stick to a 4.25 just wanted squeeze a few more cubes but its not worth burning a piston over.

  10. #8
    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by Meaddaytonamike25 View Post
    Thanks for the input guys. I guess I'll stick to a 4.25 just wanted squeeze a few more cubes but its not worth burning a piston over.
    Well for what its worth with a 4.31 bore you have 510.6 vs 496 or 14.6cid, with a 4.56 bore its 571.6-555.3 or 16.3. Like it was mentioned above with parts availability those extra few inches might not be worth the extra costs when 4.25" stroke stuff is so common.
    Quote Originally Posted by gn7 View Post
    Carnivalride, you really need to find some other hobby. You have no talent for this boat thing

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