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317 heads or 243s

This is a discussion on 317 heads or 243s within the Forced Induction forums, part of the LSx Technical Help Section category; i am swapping in a low mileage ls2 motor and wanted opinions. i have 317s on my ls1 motor and ...

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    Junior Member maxgee's Avatar
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    317 heads or 243s

    i am swapping in a low mileage ls2 motor and wanted opinions. i have 317s on my ls1 motor and was thinking of putting those on the ls2. the ls2 has the stock 243 heads on them. i wanted to try and keep the 243s for the compression, if i put the 317s, compression drops. is there a way to bring compression up without replacing pistons on the 243s?


    i've been running 8 to 12 psi on my ls1 with no issues on e85 with no issues and think i can get away with 10psi on e85 on 10:9 CR.

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    GM made me do it!! IT_SS's Avatar
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    Quote Originally Posted by maxgee View Post
    i am swapping in a low mileage ls2 motor and wanted opinions. i have 317s on my ls1 motor and was thinking of putting those on the ls2. the ls2 has the stock 243 heads on them. i wanted to try and keep the 243s for the compression, if i put the 317s, compression drops. is there a way to bring compression up without replacing pistons on the 243s?


    i've been running 8 to 12 psi on my ls1 with no issues on e85 with no issues and think i can get away with 10psi on e85 on 10:9 CR.
    if i'm not mistaken, 243s and 317s are the same cast, 243s have smaller combistion chambers which yeild a higher CR, where 317s have a larger combustion chamber, which lower compression...

    Google it

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    Junior Member maxgee's Avatar
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    Quote Originally Posted by IT_SS View Post
    if i'm not mistaken, 243s and 317s are the same cast, 243s have smaller combistion chambers which yeild a higher CR, where 317s have a larger combustion chamber, which lower compression...

    Google it
    i did, thanks

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    how much for those 243s

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    Moderator Firebirdjones's Avatar
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    If you want more compression from the 243's without a piston or deck height change,,,then milling the heads would be the way to go.


    Swapping on 317's in a boosted application on an otherwise stock motor used to be the thing to do, it was the easiest way to drop the compression for higher boost levels.

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    GM made me do it!! IT_SS's Avatar
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    I've heard that side by side, the 243 flows better than the 317 when machined to the same specs. I honestly don't see how since they're the same head minus the combustion chamber volume.....
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    Junior Member pocket rocket's Avatar
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    hey that is a good question i thought when changing heads we are only looking at the compression differenace, but is there a differenace in air flow?

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    King 0f n00bz shady milkman's Avatar
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    Quote Originally Posted by pocket rocket View Post
    hey that is a good question i thought when changing heads we are only looking at the compression differenace, but is there a differenace in air flow?
    are you talking cfms or air velocity?

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    Junior Member pocket rocket's Avatar
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    I've heard that side by side, the 243 flows better than the 317 when machined to the same specs. I honestly don't see how since they're the same head minus the combustion chamber volume.....

    this was the question about the air flow, is there a differenance between the two heads?

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