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edbird
Tribal Scout

9 Posts

Posted - 27 Mar 2017 :  3:03:41 PM  Show Profile  Reply with Quote
Hello, I am a newcomer to this forum and I seek some advice.
I have a 455 with mismatched 6x heads, one is a 6x-4 F077 and the other is a 6x-8 G or C047. My question being is there some feasible way that either these stampings are incorrect or that it is possible that the heads were machined to match? And if they were machined to match would they be worth keeping or should I seek out a matching pair? Cranking psi is 190-200 across the board, if that helps. More info on the motor: +0.030, flat top +6cc pistons, and I have no idea on the cam but it seems pretty mild. Power estimate to be around 300 bhp. Thanks

Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 27 Mar 2017 :  4:28:36 PM  Show Profile  Reply with Quote
Not too likely the cc's were matched. You would not want to mill one head significantly more than the other. It could create a fitment issue with the intake.
Assembly line generic re-builders probably don't know or don't care about different 6x heads.
Ball park compression ratio 9.5 to 1 vs. 9.0 to 1..
Probably not enough difference to create a driveability problem.



Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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edbird
Tribal Scout

9 Posts

Posted - 27 Mar 2017 :  8:11:24 PM  Show Profile  Reply with Quote
quote:
Originally posted by Blued and Painted

Not too likely the cc's were matched. You would not want to mill one head significantly more than the other. It could create a fitment issue with the intake.
Assembly line generic re-builders probably don't know or don't care about different 6x heads.
Ball park compression ratio 9.5 to 1 vs. 9.0 to 1..
Probably not enough difference to create a driveability problem.





I would agree that driveability does not seem terrible as I have been driving the car for nearly a year with no substantial issues, but I plan to make more power and have a street/strip car. Would the heads be a hindrance to this, or might they cause issues? From what I understand, the crankshaft sees different power based on bank due to the compression. This is what most worries me. I potentially have a set of 6H/46s lined up but they have the 1.96" intake valves and I'm not sure that's a good route for power.

Edited by - edbird on 27 Mar 2017 8:14:26 PM
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loosetappet
Sitting Bull

113 Posts

Posted - 30 Mar 2017 :  9:44:31 PM  Show Profile  Reply with Quote
Cranking psi of 200? Isn't that borderline for pump gas?
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edbird
Tribal Scout

9 Posts

Posted - 01 Apr 2017 :  10:04:40 PM  Show Profile  Reply with Quote
quote:
Originally posted by loosetappet

Cranking psi of 200? Isn't that borderline for pump gas?



Yeah I guess so but I don't plan on changing. I do plan on swapping the cam for something beefier and have heard that a cam with more overlap will bleed off some of that cranking pressure. I could be wrong.
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Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 02 Apr 2017 :  01:18:32 AM  Show Profile  Reply with Quote
It sounds like a small Comp cam.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Phil
The Great White Buffalo

USA
7219 Posts

Posted - 02 Apr 2017 :  1:12:30 PM  Show Profile  Reply with Quote
You'll need a quad pattern cam.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 03 Apr 2017 :  11:03:15 AM  Show Profile  Reply with Quote
6x4's are not uncommon. You should be able to pic up a single head for 1 or 2 hundred bucks. Keep checking locally, e-bay, Hemmings Motor News and Pontiac Years classifieds.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 03 Apr 2017 11:07:22 AM
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edbird
Tribal Scout

9 Posts

Posted - 03 Apr 2017 :  1:40:28 PM  Show Profile  Reply with Quote
quote:
Originally posted by Blued and Painted

6x4's are not uncommon. You should be able to pic up a single head for 1 or 2 hundred bucks. Keep checking locally, e-bay, Hemmings Motor News and Pontiac Years classifieds.



I actually just picked up a set of 6x-8s as I figured they would be better with my flat tops. So I now have 3 and will send them to a machine shop for them to decide which two are best.
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edbird
Tribal Scout

9 Posts

Posted - 03 Apr 2017 :  1:44:52 PM  Show Profile  Reply with Quote
quote:
Originally posted by Phil

You'll need a quad pattern cam.



As for a cam I was really leaning towards the XE274. It seems people have had good luck with these and it seems that it will suit my needs.

On another note, any suggestions valveteain wise? Both sets of heads have double springs on them, should I get beehives? Another thing that puzzles me is that the new to me set has some collar thing around the top portion of the springs, whereas the currently installed heads do not. Any thoughts?
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cortcomp
Coyote

USA
5335 Posts

Posted - 03 Apr 2017 :  8:27:06 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
the clacking got to me after a while, but i'm more of a worry wort than most. The lunati i swapped into my sbc recently that was similar to the XE that was in it has been quiet. If i was building another pontiac, i'd gamble on a lunati in the range of the comp cam i thought i wanted.
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