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mojonelo 09-20-2006 12:23 PM

Pontiac Heads!
hey guys
i recently bought a 68 firebird, it has a 350 pontiac in it but i have a 400 ready to go into it. the problem is that i have some 5C heads. they are 400 heads but ive never seen them in performance applications. i usually see the 6x. does anyone have any experience with the 5C's or should i go and hunt down some 6X's?

nitro_baller4692 09-20-2006 01:21 PM

here are some #'s to look at.if you are not going to go over .500'' lift on the cam 5c's are better,but if you are going to port the heads and go over .600'' lift find the 6x.
these #'s are in the right place.

port volume, 5c 151cc int./138cc exh.
6x 158cc int./146cc exh.
valve sixes
5c int.2.110''/exh1,770'' :thumbup: bigger exhaust valves
6x int.2.110''/exh1.660''
flow#'s at .500''
5c int.222cfm/exh.171cfm :thumbup:
6x int.212cfm/exh.148cfm

3xgto4spd 09-20-2006 06:51 PM

pontiac cams
need specs on a cam marked cwc gmc uas on rear it has 960940 can ya help thanx

mojonelo 09-21-2006 01:22 PM

thanks, im planning to use a mild performance cam in the engine so i dont think ill go over .5 lift or will i? another thing i have found is contradictery info. that the 5C-9 heads in one place,( they say that the 5C-9 heads are for a 350 w/A.I.R. and is saying that the 5C-9 heads are for a 400 block. Do you guys know for sure wich engine my heads are for?

nitro_baller4692 09-21-2006 03:47 PM

read this artical.

mojonelo 09-21-2006 04:09 PM

i think im going to go play it safe and find some heads off of a 400 block, again the main reason is that i dont know if these heads are for a 350 or a 400, any ideas on how to figure it out?

nitro_baller4692 09-21-2006 04:39 PM

5c heads were used on both 350 and 400's in the 70's.the 400 in 75 used 5c and 6s.the 350 in 75 use 5c but the 400 use either or.

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