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#1
01-02-2003, 12:37 AM
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I have a '76 400 in my Firebird that at some point will be re-building.
I would like to have close to 9.5:1 cr.The heads are 6x-8.Is there anyone who makes pistons that wil give me this cr? Or what pistons should I use and head milling needs to be done to achieve this? Thanks,Colin ______________________________Life is like a $h!t sandwich--The more bread you have the less $h!t you have to eat!!!
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"It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived."- General George Patton "Perpetual peace is a futile dream."-General George Patton "I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them."-Thomas Jefferson "Any society that would give up a little liberty to gain a little security deserves neither and will loose both."-Benjamin Franklin |
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#2
01-02-2003, 12:37 AM
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I have a '76 400 in my Firebird that at some point will be re-building.
I would like to have close to 9.5:1 cr.The heads are 6x-8.Is there anyone who makes pistons that wil give me this cr? Or what pistons should I use and head milling needs to be done to achieve this? Thanks,Colin ______________________________Life is like a $h!t sandwich--The more bread you have the less $h!t you have to eat!!!
__________________
"It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived."- General George Patton "Perpetual peace is a futile dream."-General George Patton "I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them."-Thomas Jefferson "Any society that would give up a little liberty to gain a little security deserves neither and will loose both."-Benjamin Franklin |
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#3
01-02-2003, 04:27 AM
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The 6X-8 heads will be 98-101cc, compression ratio stock is about 7.7 to 1. At best you could cut them .060" and get to about 8.6-8.8 to 1. You can start with a set of 6X-4's, they are closer to 92cc and cut them for over 9 to 1. I'm not a big advocate of cutting heads to death to get more CR, but it does work. Domed pistons will work, but are expensive and generally frowned upon in Pontiac engines. Best course of action would be to obtain an early set of 13's or 62's.....Cliff
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#4
01-02-2003, 11:31 AM
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Ciff is pretty close on the ccs. My 6X-8 on my originial 78 motor c'd 97.5 after a 0.003 cleanup.
The 6X-4s I'm working on now have two different castings so one' probbaly not the original on the motor I pulled them off of. One measured 92.0, the other 91.0. I'm going through the same thing with a new 400. I'm going to mill the 6X-4s down to around 85ccs and zero deck. My virgin 78 block was 0.012 down on deck height with those 97.5cc is about 8.22 on my program, so pretty low.I don't know if you can mill them enough to drop the 6X-8s low enough without some fancy angle milling that can throw off the exhaust angle for your manifolds/headers.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#5
01-04-2003, 10:47 PM
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Alright,thanks guys.I only assumed that my heads are 6X-8s but they are actually 6X-4s,I looked today.According to the compression ratio calculator on the Ross pistons site if I zero deck my block,mill the heads to 82cc(according to Wallace racing I need to mill .0475 to drop 10cc to give me 82cc) and use the TRW forged flat tops I should get 9.58:1.Thats with compressed gasket thickness of .040.Dunno,something doesnt sound right to me.Any thoughts on this?If the heads are milled that much will it throw the geometry off?
Thanks,Colin ______________________________Life is like a $h!t sandwich--The more bread you have the less $h!t you have to eat!!!
__________________
"It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived."- General George Patton "Perpetual peace is a futile dream."-General George Patton "I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them."-Thomas Jefferson "Any society that would give up a little liberty to gain a little security deserves neither and will loose both."-Benjamin Franklin |
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#6
01-05-2003, 04:17 AM
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Your calculations are close. At a minimum you will need to have the intake cut to fit and probably need shorter pushrods. For all the added expense you could have used a set of 62's or 13's and been there to start with....just my 02.....Cliff
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#7
01-05-2003, 09:44 AM
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Two things that make the 6X-4s different from the 6X-8s. Chamber on -4s is slightly smaller diameter when compared to a head gasket as they were the 350 heads. Also a little bit shallower.
Vlave length onthese is a question. My shop manual lists them as 4.86 length. the ones I just took out were 4.96 or so. So doing some ballpark math if the 4.96 valves are stock and stock pushrod. A 0.015 decking and 0.045 milling may keep the valve tip close enough(.100 longer but dropped .060 in relation to block where pushrod locates from) to use stock length pushrods when using the typical 5.100 valves?
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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