Which heads??
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Which heads??

  1. #1
    Senior Member Chop Shop's Avatar
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    Default Which heads??

    I am bolting together some junk.

    Need advice an what heads to use.



    Lower end is a BBC 468 with flat top pistons. Single plane, single carb intake. Headers. Camshaft is a hyd flat tappet CompCams 280H, .520 lift 230 duration at .050.


    I have two pairs of heads I can use.

    One pair are 781 castings oval ports with nice hardware with 2.06/1.72 valves.

    The other pair are 088 rect port heads with 2.19/1.88 valves.

    Both pairs are near new and very low hours. Same wear on both sets.


    Would this 468 and cam combo make more power with the rect port heads or the smaller oval ports?

    Would the power be simular with either head, just in a different RPM range?

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  3. #2
    Senior Member motor head's Avatar
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    More air flow = more rpm = more hp.
    My 02. Keep combustion chamber (compression ratio) in mind.
    [SIGPIC]

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    Senior Member Chop Shop's Avatar
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    Quote Originally Posted by motor head View Post
    More air flow = more rpm = more hp.
    My 02. Keep combustion chamber (compression ratio) in mind.
    That is correct.


    But with flat tops and the cam chosen, I know that sometimes too much airflow will hamper power output.


    Without a huge camshaft and big compression, I worry about the rect ports not really performing any better then the oval ports I have.


    I am not changing the lower end (pistons/CR and cam profile) just need to decide whick heads will work best with this combo.

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    Senior Member motor head's Avatar
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    I would say the air flow of the heads isn't going to hurt it will actually help you make more hp. It's the overlap of a cam that will cause a need In more CR. I could see where if the heads had huge ports they could hurt. Again this is just my opinion, I'm not a professional engine builder!
    [SIGPIC]

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    Just a thought, if this is going into a jet, what pump and impellor are you using? Or another way of looking at it is what RPM are you expectng to turn? At some point, the 781's will not flow enough but should be ok up to about 6500 Rpm. Others may have more detail but this is a ballpark idea.

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    Its a jet, no impeller yet.

    Its not gonna be spinnin 6500. The lower end is not anything baddass, just fresh and tight stock stuff.


    Theres a point where intake volume being larger can hurt without compression/cam. The cam I have is going to pretty much dictate what RPM it makes power at to a degree, correct?



    Just looking to see if the larger heads would help or hurt. Volume without velocity is not helpfull, correct?

  9. #7
    Senior Member motor head's Avatar
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    He may not be able to get hp @ 6,500 out of that cam and smaller heads but will with that cam and better heads.
    [SIGPIC]

  10. #8
    gn7
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    Quote Originally Posted by motor head View Post
    More air flow = more rpm = more hp.
    My 02. Keep combustion chamber (compression ratio) in mind.
    So you know the flow capabilities of the rectangle port BBC head to know he needs them for a .520 cam? Wheres the cork in the system here motor head? The heads flow, or the cams lift? What happens when you have that much port and not enough cam lift to use it. Is there in you mind such a thing as TOO much port?

    Lets see 2 1250 Domintors=lots o air
    .900 lift cam with 280 duration at .050 (with a 114 LSA so hold down the overlap)= lots o air
    385 cc Dart Pro 2 heads= lots o air

    Sounds like the perfect combo for a 396 with 9 to 1 to me



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    Quote Originally Posted by gn7 View Post
    So you know the flow capabilities of the rectangle port BBC head to know he needs them for a .520 cam? Wheres the cork in the system here motor head? The heads flow, or the cams lift? What happens when you have that much port and not enough cam lift to use it. Is there in you mind such a thing as TOO much port?

    Lets see 2 1250 Domintors=lots o air
    .900 lift cam with 280 duration at .050 (with a 114 LSA so hold down the overlap)= lots o air
    385 cc Dart Pro 2 heads= lots o air

    Sounds like the perfect combo for a 396 with 9 to 1 to me

    GN if you came in here just to argue and to disprove others, please dont.

    If you came here with good advice pertaining to the thread, please do.

    Mk,Thnx

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    Not to start up the HP or Torque war again but it is torque that turns the pump. So max rpm will be at the speed the engine torque matches the torque required to turn the pump at that Rpm. Hp is a number that occurs as a result of that and is not the driving factor. If the bottom end is fairly stock, go with the 781's, set your pump up to turn about 5-5500 Rpm with parts you have and enjoy the boat. Parts stay cheap and you will have good reliability. You can always save the 088's for another build or sell them to buy gas for the boat. Would you notice a seat of the pants difference between the engine with the 781 or 088's? Probably not but your engine will be crisper with the 781's.

  13. #11
    Senior Member motor head's Avatar
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    Quote Originally Posted by gn7 View Post
    Quote Originally Posted by motor head View Post
    More air flow = more rpm = more hp.
    My 02. Keep combustion chamber (compression ratio) in mind.
    So you know the flow capabilities of the rectangle port BBC head to know he needs them for a .520 cam? Wheres the cork in the system here motor head? The heads flow, or the cams lift? What happens when you have that much port and not enough cam lift to use it. Is there in you mind such a thing as TOO much port?

    Lets see 2 1250 Domintors=lots o air
    .900 lift cam with 280 duration at .050 (with a 114 LSA so hold down the overlap)= lots o air
    385 cc Dart Pro 2 heads= lots o air

    Sounds like the perfect combo for a 396 with 9 to 1 to me



    I don't want to get over your head. Lol
    I said I wasn't a professional builder and I did use the words may because I have no idea what the heads flow or how big the ports are.
    [SIGPIC]

  14. #12
    Senior Member Chop Shop's Avatar
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    Quote Originally Posted by motor head View Post
    I don't want to get over your head. Lol

    But he did manage to get you under his bridge.

  15. #13
    Senior Member Smallblocksperry's Avatar
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    Quote Originally Posted by gn7 View Post
    So you know the flow capabilities of the rectangle port BBC head to know he needs them for a .520 cam? Wheres the cork in the system here motor head? The heads flow, or the cams lift? What happens when you have that much port and not enough cam lift to use it. Is there in you mind such a thing as TOO much port?

    Lets see 2 1250 Domintors=lots o air
    .900 lift cam with 280 duration at .050 (with a 114 LSA so hold down the overlap)= lots o air
    385 cc Dart Pro 2 heads= lots o air

    Sounds like the perfect combo for a 396 with 9 to 1 to me




    This guy, always arguing with everyone, acting like he knows everything there is to know, he's not talking about putting 385cc heads on it, he's talking about gm iron fuckin heads, run the rectangular heads and ignore this guy

  16. #14
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    If the heads are to big for the engine you will lose velocity, and fail to fill the cylinders. bigger is not better.

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