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317 vs. 243... question

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Old Dec 3, 2008 | 11:02 PM
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Default 317 vs. 243... question

I have a 05 LQ9 6.0 with the 317 heads.... how can I get them to flow just like the 243? If I am not mistaken they flow the same except for the cc's being different. What can I do to have them exactly like Z06 heads? I have heard bout getting them Milled? And in Shaving them down would I have any issues such as piston to valve issues? And how much would it run me to get the heads shaved down?
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Old Dec 3, 2008 | 11:10 PM
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Also would milling down my heads cause compression problems such as having to much if thats even posible?
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Old Dec 3, 2008 | 11:11 PM
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.040 mill will = 10.25 on lq4
ptv will be determined by size of cam used. must check ptv with any cam used anyway, also will affect pr length some, again need to check for correct pr length.
.040 will be enuff to mill,more than that may have manifold alignment issues317 flow just as well as 243.
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Old Dec 3, 2008 | 11:16 PM
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Cam I am running is GM Hot Cam 218/227 .525/.525 112 , 03-04 LS6 Springs , on a 05 LQ9
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Old Dec 3, 2008 | 11:28 PM
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if its a lq9 then theres no need to mill heads for more scr,
since you are alredy at 10:1 compression, stock
that cam should have no affect on ptv clearnace since its lo duration and lift.
if the heads are alredy off, then a good .020 mill will bump up the scr some.
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Old Dec 3, 2008 | 11:32 PM
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scr? What does that mean? Would it make any difference? I also have an LS6 Intake if it makes any difference? And how much does it run to mill heads?
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Old Dec 4, 2008 | 09:38 AM
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SCR = Static Compression Ratio. It is the compression ratio based on the head CC, piston design, bore and stroke ... while not considering pumping losses when the cam events are considered.
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Old Dec 4, 2008 | 04:27 PM
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243s on your LQ9 will bring you up around 11:1
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Old Dec 4, 2008 | 06:28 PM
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Would 11:1 be bad??? I am noob to the compression stuff. If anything I would spray about a 100 shot other than that should be seeing anymore mods.
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Old Dec 5, 2008 | 08:46 PM
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I am at 11.3-11.5 and have no problems. N20 loves compression as well. you could get away with 12.0-12.5 depending on the gas you have available.
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Old Dec 6, 2008 | 02:15 PM
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I run Super unleaded all the time.
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Old Dec 6, 2008 | 03:36 PM
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I would sell the 317's to someone that is going FI as they like those heads as it will lower the compression a point on a ls1 and the go out and buy a set of ls6 heads.
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