Big Block Heads

Discussion in 'Engine Topic' started by ultimateoffroad, Jan 19, 2021.

  1. ultimateoffroad

    ultimateoffroad Veteran Member Lifetime Gold Member

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    I was cleaning up the 396 to put it into the 79 and would like some feedback. The 396 ran great before I pulled it out of the 71 fyi.

    The block number is 3999290 which is either 396 or 402.

    After pulling the intake I see that they had a square port intake on the oval port heads. I do have a BB oval port Edelbrock Air Gap intake I can put on it.

    The current heads are 6272292. I have a set of head on the shelf that are 3856206 that supposedly were rebuild by po and have gold aluminum roller rockers.

    Is it worthwhile swapping these heads or just run the way it is?
     
  2. carhead22000

    carhead22000 oldblue

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    if you have a good set put them on. Might as well re ring and put new bearings in it and a cam to match heads if its in budget.if not and you were happy with the way it ran,put it in.i would freshen it up myself.use the airgap.
     
  3. 450bench

    450bench Veteran Member

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    Your current 292 heads are probably in the 112 cc chamber range and are good heads with unique chambers like an old 820 head. the 206 heads are true closed chamber bathtub Style and are in the 96-98 cc range so you’ll get more compression with them.
     
  4. G72Zed

    G72Zed Veteran Member

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    Using the rectangle port intake on the Oval port heads was/is a common performance modification.
     
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  5. ultimateoffroad

    ultimateoffroad Veteran Member Lifetime Gold Member

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    Yeah probably going to
     
  6. ultimateoffroad

    ultimateoffroad Veteran Member Lifetime Gold Member

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    Which would you run?
     
  7. ultimateoffroad

    ultimateoffroad Veteran Member Lifetime Gold Member

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    Good info. is there a benefit to this. I thought it would cause some sort of flow issaue
     
  8. G72Zed

    G72Zed Veteran Member

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    Yes there is a benefit, but like every combo is different, and there's always the exception.

    It's one of those things when you see it for the first time, like WTF are you doing....but it works.

    Think of the big cams with reverse flow and reversion/pressure waves, air does not like large changes in area, everything slows down, sometimes working it backwards pays more dividends then the other way.

    Ford big block marine had the same phenomena/history.
     
  9. 450bench

    450bench Veteran Member

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    If I had both sets I’d run the 206 heads. If I only had the 292s I’d run them and not buy another set. Hope that makes sense.

    Imo, a rectangle port intake on oval port heads is fine. I’ve done it too many times to count. Works great. Just use rectangle port gaskets.
     
  10. 1980RS

    1980RS Veteran Member

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    You can run the Sq. Port intakes on the oval and peanut port heads but the last time I did that swap and in the past my engines have always hit the 5500 RPM stall point, it this is just a cruiser I don't think it would hurt anything. I do know that ovals or a good set of peanut port heads really wake up a 396.
     

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