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compression

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    hi iam a slow typer so i got 454 bbc ls6 450hp? square port heads#188 with small dome pistons (factory) thought comp was 10.5 but been reading it is only 9.0 ok so want to change heads most will not work with these pistons if i go with flat tops and same chamber i wont have any comp ? left. how do i get it back to 9.0 /9.25 thanks

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    Some guy obnoxious001's Avatar
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    What are you looking to achieve by changing the heads? Seems like you only gave us part of the story?

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    To know the compression, you have to know the size of the domes, likely the hardest figure to come up with.

    Chamber volume can be typical, and researched, bore and stroke, as well as typical gasket thicknesses, fine to get a "ballpark" figure, but without a decent idea of dome CC, mighty hard to figure out the compression ratio.

    As obnoxios noted, exactly what is your goal/purpose? We need more info here.
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    trying to get more hp/torque they say aprox 100 hp with newer style heads and cam (already got intake and exhaust) but most newer heads wont work with stock dome pistons

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    Senior Member VDRIVERACING's Avatar
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    It's important to know which heads you have. The LS6 came with either a closed chamber (1970) or open chamber (1971 and later crate motors).

    BTW, if you have 1970 or '71 original LS6 heads, you could sell those for a few bucks to someone restoring an old Chevelle.
    Last edited by VDRIVERACING; 08-30-2009 at 05:02 PM.

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    open chamber

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    Quote Originally Posted by ibelio View Post
    trying to get more hp/torque they say aprox 100 hp with newer style heads and cam (already got intake and exhaust) but most newer heads wont work with stock dome pistons
    Well, then you are, IMO, best off served by not trying to short-cut yourself into a problem.

    Select a new head and a piston to match to the aproximare CR you desire, and give the engine an overhaul.
    Easilly doable, if you are wrench savy. for under a grand, plus the heads & pistons.
    If you have to pay an assembler, price goes up.

    Otherwise, you have to pray that as new head both:
    fits to your pistons
    and
    fits CLOSER to your pistons than the old ones did, to get a higher CR.

    Better be in good with the lord, VERY good.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
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    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

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    Senior Member CK7684's Avatar
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    Why not change the pistons instead?

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    Quote Originally Posted by CK7684 View Post
    Why not change the pistons instead?
    That would do, but, IMO, unless he is planning to spin that engine above 6-grand, the big rectangle ports are going to fight him, and would be much better off feeding a 454 with good large ovals with the large valves.

    I'd change the pistons first, especially if money was an object, but I'd be trying to plan on a head change at some point, without making it much more work again, a piston to work with this head, that would work better with a future head, if possible to find that way.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

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    this is what i was thinking not going above 6 grand 37.6 scarab twin 454 bbc

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    Sit N' Spin Jetaholic's Avatar
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    OK..your best bet in this case it to add some...



    I'm sure "Smokin' Pole Rider" would wholeheartedly agree with going this route. Matter of fact, the one thing he taught me that I 100% agree with is to -

    1) Add a 500hp shot of nitrous

    2) With that 500hp shot of nitrous...you'll want to make ABSOLUTELY 100% SURE that you have a cam that calls for the valve to be open right at TDC

    With this combo, it's a 50/50 chance that you'll be able to spin an Aggressor B impeller @ 5000 off the bottle, and I'd say about "5150" on the bottle...maybe.



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    You need CUBES. The heads you have will support 600 HP as is bone stock if you had some inches underneath them. You have a heavy boat so better to do it with torque. Put 2 496 rotating kits under those heads, cam to run 5600 or so and you can have some nice 550 to 575HP mills that will run all day long.
    Chris Straub
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    3HP is an A$$ Whooping!!! JW

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    Quote Originally Posted by cstraub View Post
    You need CUBES. The heads you have will support 600 HP as is bone stock if you had some inches underneath them. You have a heavy boat so better to do it with torque. Put 2 496 rotating kits under those heads, cam to run 5600 or so and you can have some nice 550 to 575HP mills that will run all day long.
    Yes, that would net the most gains, stroke the 454's, the heads are not too big for a larger engine, properly set up (cammed, intake, exhaust), would be a very strong and solidly reliable setup.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

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    i like that idea probaly go that way. p.s. will need to talk to chris about cam for this plan thank you guys

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