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Heads: 6S #9 vs 6X #4 - Any difference?

  
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Heads: 6S #9 vs 6X #4 - Any difference?

 
Code400 Code400
New User | Posts: 34 | Joined: 02/13
Posted: 02/28/14
02:46 PM

All the specs look the same for these heads
93.74 cc  2.11/1.66

These look like a nice fit for a mild 400, why is it that the 6X's are almost double the price everywhere I look?  






Code400
1967 Firebird 400
TH400
3.73

69GTOby 69GTOby
Guru | Posts: 1114 | Joined: 02/09
Posted: 02/28/14
06:48 PM

I do not know for sure, hopefully someone else does.  But, I will say that perhaps the 6x's have screw in studs while the 6s's do not?  Also, one may have a more desirable chamber design or better flow ratings...  I don't know.  Just a couple thoughts...  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 450 | Joined: 11/13
Posted: 03/01/14
02:28 AM

Those heads are not all the same cc or fit the same year etc. see chart below. All head chambers should be measured and the amount they have been surfaced from stock should be determined to know EXACTLY what you have.

they are all screw in rocker studs.

http://ronspontiacpage.com/reference-pages/stockheadspecs.htm  

Pontiacman8 Pontiacman8
Moderator | Posts: 5775 | Joined: 02/08
Posted: 03/01/14
08:13 AM

1975/79 Stampings on Head codes - 6X / 6H

Year Stamped ID Head # Code MVMA Chamber Vol. Valve Diameter Valve Length CID
1975-76 4 6X 93.74 cc's 2.11/1.66 valve 4.86" 350
6 6X 124.51 cc's 2.11/1.66 valve 4.71" 455
6 6H 124.51 cc's 2.11/1.66 valve 4.71" 455
7 6S (AIR) 100.04 cc's 2.11/1.66 valve 4.86" 400
8 6X 100.04 cc's 2.11/1.66 valve 4.86" 400
9 6S (AIR) 93.74 cc's 2.11/1.66 valve 4.86" 350
1977 4 6X 93.74 cc's 2.11/1.66 valve 4.86" 350 / 400 W72
8 6X 100.04 cc's 2.11/1.66 valve 4.86" 400
1978 8 6X 100.04 cc's 2.11/1.66 valve 4.86" 400
1978/79 4 6X 93.74 cc's 2.11/1.66 valve 4.86" 400 W72  
Engine builder,self taught auto body guy.
Horsepower sells engines and torque wins races

Pontiacman8
Pontiacman8
Pontiacman8

Code400 Code400
New User | Posts: 34 | Joined: 02/13
Posted: 03/01/14
09:49 AM

Oh I see, well now that I've cleaned off the top of the pistons I can see they're .060 over, now I'm not really sure what to go with? I was thinking of the 6X 4 heads for around 9.5.1 compression, how greatly does the .060 over change this? The '68 #15 72cc pressed stud heads came off this motor and it seemed to run great with 91 octane. Maybe I can go with another 72cc head with the large valves and screw in studs?? I'd like to change out the cam and heads, run this 400 for a while so I can slowly build a 455 of my dreams, which will take a while do to funds. This current 400 appears to be stock '68 bored .060 over with relatively low miles. What do you think about running the large valve 72cc heads (#12, 13) and new cam/lifter kit? Thanks!




1967 Firebird 400
'68 400
TH400
3.73's  






Code400
1967 Firebird 400
TH400
3.73

ROWSLEY ROWSLEY
Guru | Posts: 1015 | Joined: 07/11
Posted: 03/02/14
02:53 PM

6s heads(california) are air injection heads, extra holes in exhaust ports. other than that they would be the same specs but may not flow as good as the 6x.

the 6x 4 head will give you 8.6 to 1 with a .060 flat top piston. 72cc head will be 10.0 to 1.

have you ever checked total timing?  
76 455/4spd TRANS AM
69 GRAND PRIX 455/5SPD

69GTOby 69GTOby
Guru | Posts: 1114 | Joined: 02/09
Posted: 03/03/14
08:00 PM

Maybe you should put some money into the #15 heads you already have.  They're 72cc which should give you about 10:1 which is great.  You can get put oversized 2.11/1.77 valves in, get them ported and polished, get the pressed in studs pulled out in favor of screw in 7/16" studs and they will be great!

What do your pistons look like?  What kind of shape is the rest of the motor in?  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.

Code400 Code400
New User | Posts: 34 | Joined: 02/13
Posted: 03/03/14
09:58 PM

That definitely has crossed my mind. I've been short on time, haven't even taken the oil pan off.... Pistons look fine and the engine does run great. I should have the pan off sometime tomorrow if I get a damn minute a free time. I am a little confused about the compression. Some on here have said 10.5 to 1, 10 to 1, others 9.75 to 1, online calcs show 11.5 to 1 with the .060 bore?? This is the difference between running pump gas or not so I'm a little clueless on what to do, I don't have $$ for Eddy's. I'll cc the heads (15's) and look at the lower end and post an update, thanks all!  






Code400
1967 Firebird 400
TH400
3.73

69GTOby 69GTOby
Guru | Posts: 1114 | Joined: 02/09
Posted: 03/09/14
10:09 AM

Those online calcs are good tools, but only when they are used correctly.  You must measure EVERYTHING to know for sure what your static compression will be.  You said you have flat top pistons.  Do they have 4 valve reliefs or are they crappy 8 valve relief pistons?  

You need to measure the piston to deck clearance at TDC, as well.  They could be .040 down the hole or even .020 above the deck.  It depends on the pistons and if the block has been decked.  

The head gasket dimensions will make slight differences, too.  You can kind of fine tune your CR during assembly considering different head gaskets.

Obviously the head chamber volume should be measured.  The advertised specs do not always match what they actually come out to be, especially on 45 year old heads that have endured several valve jobs recessing the valves further into the chambers increasing the volume.

You need these pieces of information.  You can go even further and measure the piston valve relief volume and the space added between the top compression ring, cylinder wall, and the piston, and probably more little stuff.

On 93 octane pump gas with iron heads you can run 9.2 up to 10:1 SCR successfully.  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.