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455 6S heads on a 400?

  
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455 6S heads on a 400?

 
Code400 Code400
New User | Posts: 34 | Joined: 02/13
Posted: 02/24/14
09:59 PM

Hi all, I came across a set of really nice '75 6S heads for cheap. I was thinking of removing my #15's with the pressed studs and throwing these on with a new cam & lifter set. I can only get 91 octane in CA and I'm on a really tight budget. I'm really not familiar with the 6S heads other than knowing they have the larger valves, screw in studs, and have a smaller cc. A local Pontiac oldtimer really likes this set up with the 068 grind. There's not a whole lot of chat about these 6s's either.....looking for input/advice.

1967 Firebird 400
'68 400 engine, Eddy intake and Holly DP, LT headers.
TH400
373's  






Code400
1967 Firebird 400
TH400
3.73

ROWSLEY ROWSLEY
Guru | Posts: 1016 | Joined: 07/11
Posted: 02/25/14
07:12 PM

6s heads were used on 75/76 400 and 455s the 400 heads would have a secondary #of 7 and 98 to 101cc witch would yeild 7.6 to 7.9 compression to low for the 068. pontiac use a 066 you might get away with a little bigger but not much.

if their 455 heads your talkin 6.6 to 1 at 124cc

look for some 350 heads with 91cc or #96,7k3 96cc 400 heads and have them milled to 90cc 8.4 to 1 then the 068 will work. by the way cams have come a long way in 45 years!

check out http://www.wallaceracing.com/ (Cylinder Head Codes)  
76 455/4spd TRANS AM
69 GRAND PRIX 455/5SPD

Code400 Code400
New User | Posts: 34 | Joined: 02/13
Posted: 02/25/14
08:00 PM

Yeah, I was thinking something along those lines but this old dude really confused me  Confused Haha! He has dozens of motors, heads, etc. and sounded like he knew what he was talking about. I'll go a different route, thanks Rowsley!  






Code400
1967 Firebird 400
TH400
3.73