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Thread: 4 Bolt Caps

  1. #1
    Thank you from BT Master (OIIIO)
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    4 Bolt Caps

    Does anybody make 4 bolt main caps?

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    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    Pro-Gram Engineering. http://www.pro-gram.com/

    I believe it's a 401 mod, as the main webs are thinner on the 304/360 blocks and don't have enough meat to drill bolt holes.

    Remember that the block will also have to be line bored after installing the caps.

    Bob
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  3. #3
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    Quote Originally Posted by tufcj
    Pro-Gram Engineering. http://www.pro-gram.com/

    I believe it's a 401 mod, as the main webs are thinner on the 304/360 blocks and don't have enough meat to drill bolt holes.
    Hmmm, I thought that there were thicker casted 360 blocks that would support this mod?

    Quote Originally Posted by tufcj
    Remember that the block will also have to be line bored after installing the caps.

    Bob
    tufcj
    Yup, sure do... Standard practice.

  4. #4
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    Quote Originally Posted by fifesjeep

    Hmmm, I thought that there were thicker casted 360 blocks that would support this mod?
    Yep but those blocks are very hard to come by, I think they were cast for Trans Am racing.
    1979 Jeep CJ-7 401 AMC, GMC 6-71 Blower 10% overdrive, Bugcatcher with electronic fuel injection and a little N2O for fun, all self built. (this supercharger stuff is easy)

  5. #5
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    Quote Originally Posted by Blown7
    Quote Originally Posted by fifesjeep

    Hmmm, I thought that there were thicker casted 360 blocks that would support this mod?
    Yep but those blocks are very hard to come by, I think they were cast for Trans Am racing.
    Cool, makes sense. I'd be nice to stumble upon one in good shape.

  6. #6
    Helpfull BT forum member Swabie
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    360 block

    Quote Originally Posted by fifesjeep View Post
    Cool, makes sense. I'd be nice to stumble upon one in good shape.
    Yes they were used in Trans Am but some of the later service replacement 360's came with the thicker webbing. I remember seeing one in a 74 Javelin that had a factory motor repalced in the mid 80's and it had the thick webs. Only one I ever saw

  7. #7
    Bulltear forum member New to the forum
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    The one at 74 Javelin was good enough. I still wonder why they did not make more in any of those ever.
    Everyone, take one... repo trucks for sale

  8. #8
    Thank you from BT Tech Master Bulltear Forum
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    The factory service blocks were basically a blank with slightly heavier castings, it was up to the final user what they were at the machine shop (304/360) IIRC

  9. #9
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    My first post here. AMC 1970 390 and all 401's will accommodate 4-bolt mains. The "service block" is as described above. It has the same bottom end as the late 390 and all year 401 and was a 4.08" bore 360 cylinders with enough material in the cylinder bores for the service department to bore to 4.165" 390 / 401 specs if required. There were some smaller 290 engine blocks made with 4-bolt provisions but that was a Trans-Am race block and very rare indeed.
    Milidon and Pro-Gram Engineering make excellent 4-bolt main caps. Milidon availability can be iffy, Pro-Gram will get them to you in a reasonable amount of time. You can buy the three middle caps with 4-bolt. Pro-Gram also offers billet #1 & #5 caps but those are 2-bolt. Just keeps the billet theme going. I have all 5 on my '70 390 race engine. You will need to line bore / hone ANY block if you change the caps (even if factory standard caps). Caps are married to the bore.

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