#61  
Old 12-14-2020, 11:16 PM
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Originally Posted by Jay S View Post
I dug the 48 out and cc’d it. Been in storage awhile, a little different than I remember it. It wasn’t beed blasted like I remember and I thought it was a bare head. Lol. So I am not batting 100% on what I remember. But I cc’d it again at 71-72.

The date code is f179. Very late 69 head. I also notice a X stamped on the head above the 4 on a head boss. Probably means something, just not to me. . Could be a machining or set up designation. I.E. similar to what Steve25 mentioned.
Interesting I have F189 just down the road from you from Shenandoah. Too bad Im late to the party.
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Old 12-15-2020, 07:15 AM
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Does it have an 'X' stamped on it?



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Old 12-15-2020, 02:15 PM
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[QUOTE=johnta1;6205689]Does it have an 'X' stamped on it

Yes it does, It is a little higher. But in same spot above the 4.
John

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Old 12-15-2020, 02:27 PM
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COOL!

Can you post a pic of the head?



BTW, is it just one head also?


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Old 12-15-2020, 02:50 PM
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X's on Pontiac heads is many times a designator for a special spring package which is what we would expect to find on a 48 casting.

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Old 12-15-2020, 03:36 PM
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COOL!

Can you post a pic of the head?



BTW, is it just one head also?

Yes one head.
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Old 12-15-2020, 03:37 PM
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All #48 heads uses the same springs from factory.

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Old 12-15-2020, 08:46 PM
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The AMA specs for 1969 show the 350HO having a compression of 10.5. The 400 RA has a compression of 10.75. That would indicate the same chamber size?

The 350HO and RA heads used different spring pressures depending on auto or manual and cam used.

In the 1969 Super Stock magazine, the article on the 350HO Firebird build states that Milt was sure to get the head chambers to exactly 61.2 CC's. How much of a mill would that take?

The "X" on the head that was provided may have indicated something as simple as an oversized valve - ie a fix or repair of some sort. Minor blemishes or some other fixable repair would be done before they tossed out a part that could be salvaged. I think we have all heard, and or seen, the stories where an engine had 1 piston oversized or 1 bearing undersized. I myself have seen a 70's era Ford head that the rocker arm pedestal was not fully formed from casting it and the factory built it up with weld and machined it for use as a production head.

Pontiac used the same 400CI cast piston from 1967-1974. The RAIV used a forged piston said to have been 50 grams lighter than the cast piston.

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Old 12-15-2020, 08:58 PM
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The bore is a lot smaller on the 350, making the same size chamber too big to make 10.5 CR. (would be 9.25 CR with 72 cc)



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Old 12-15-2020, 10:17 PM
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Quote:
Originally Posted by johnta1 View Post
The bore is a lot smaller on the 350, making the same size chamber too big to make 10.5 CR. (would be 9.25 CR with 72 cc)


Agree. But, advertised compression specs were as we know fudged in many instances OR used for the NHRA racers.

Just for fun, I used the Wallace Compression Calculator. 350CI, 61.2 cc's, 6.6 valve reliefs, .038" thick head gasket (which I found in the HO Parts listing), .016" deck height, 4.0" dia head gasket? (not sure what is correct here) and I come up with a compression of 10.21.

And, the 350HO had a scallop in the upper cylinder for valve clearance. Did this have an effect on compression?

If a Pontiac 400 head gasket of .022" (compressed thickness) x 4.2" dia. was used with the above numbers, the compression becomes 10.55 - fairly close to the advertised 10.5 compression.

Now this article on the 1969 Lemans 350HO says the head chamber was 66CC's on the original head. I included a photo of the chamber - which some might see a difference when compared to other #48 heads.

https://www.hotrod.com/articles/hppp...-engine-build/

Here is a Hemmings article on the 1969 Firebird 350HO and it too says 66CC's.

https://www.hemmings.com/stories/art...c-firebird-h-o

So just a few more things to throw into the mix to stir it up. LOL

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Old 12-16-2020, 06:07 AM
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Quote:
Originally Posted by PontiacJim1959 View Post
The 350HO and RA heads used different spring pressures depending on auto or manual and cam used.
Source on that?

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Old 12-16-2020, 06:49 AM
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My info from one of McCarthys books show that the 48 castings in the A body cars all used the standard int and Exh spring set up as all the other 4 bbl D port heads, it was the 48 castings that where bolted on the F body 400s that got a different spring package.

I need to go and look again as I can recall which valve got the different spring and if it was a inner or outer.

Its interesting to note that in 69 and 70 the D port ram air motors reverted back to using standard D port lenght valves which took them back to somewhere around a 1.609" installed height as opposed to the D port 1968 casting 31 that left the factory with a 1.731" installed height.

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Old 12-16-2020, 02:49 PM
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Late 1967 and early 1968 RamAir engines uses #9785999 inner and #9785998 valve springs installed@1.712" with standard length valves, same as 1969 and 1970 D-port RamAir engines, due to deeper machined spring pockets.

The only 1969 400 RamAir III Firebird with different valve springs was code YW, this engine got the 067 cam and #62 heads.
Again, all #48 heads got the same springs.

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Old 12-16-2020, 03:55 PM
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I'm still just following my curiosity here but haven't seen anyone list part numbers to confirm the existence of 2 different chamber volumes on these 48 castings.

Clearly people measure 2 ranges of chamber volumes so it is logical to exist two versions were made.

If these 2 volumes were needed to support applications, I still expect 2 unique part numbers AND a way to identify them by a physical inspection of the head. The "X" might be an example of an indicator.

So.... even if PNs were not stamped on the heads, were there 2 different part numbers in the system/catalogs for bare head castings and/or head assemblies known to have the same 48 casting number?

I now understand there was only one spring config across multiple engine applications so I would not expect a different PN of the assemblies to be driven by different springs and/or valves.

I still want to know if you could put a single 66cc head on an engine with the other head being 70-72cc without causing issues? If so, then I can't think of a reason to have 2 unique PNs. If not, then I would still expect a difference in PN and markings to distinguish.

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Old 12-16-2020, 05:06 PM
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Default same springs?

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All #48 heads uses the same springs from factory.
I am a little confused by this. Earlier you posted a scan of a parts book showing the springs changing at engine number 709186, presumable corresponding to a cam change from 744 to 068. Are you saying that the #48 heads were used only on one side or the other of this change?

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Old 12-16-2020, 08:18 PM
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ok, I'd like to speak up, without stirring the pot;
Maybe in this back and forth something has been forgotten;

I have understood that the "72cc" was a nominal rating that Pontiac advertised for both s/t and a/t applications of their engines ect?

I had understood that typically, the 48/12 would spec in at 67cc, and that the 62/13 would spec in somewhere closer to 78cc;
If my recollection is correct that is roughly a 5cc variance for each casting from the nominal rating.

Now I am not an expert on how these were manufactured, but isn't it possible that some castings had larger than intended combustion chamber sizing?
(which is why I seem to also recall reading of 13/62 heads that measured more like 80cc's?)

From everything I have read, the assertion that the casting number dictated combustion chamber size should be correct.

Variance in manufacturing might just be at play with that "48-X" head... or maybe it was marked as "X" because it was a factory reject, and not originally used because the chamber was made wrong.

Thoughts?

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  #77  
Old 12-16-2020, 11:02 PM
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Quote:
Originally Posted by Kenth View Post
Source on that?
The AMA specs published 9-12-68. The differences are slight in my opinion, and could even be a typo. The 400RA manual/auto almost look reversed? But maybe this was done on purpose to limit RPM and cause early valve float in an effort to save the engine and limit warranty work? Closed spring pressures are the same for both engines EXCEPT the manual 400 RA Intake Inner. The differences are in the open pressures & spring height.

350HO Manual Intake Outer Spring - Open Pressure 192.72-206.72 @1.177"
350HO Automatic Intake Outer Spring Open Pressure 191.6-205.6 @ 1.181"

400 RA - Manual Intake Outer Spring - Open Pressure 192.44-206.44 @ 1.178
400 RA - Automatic Intake Outer Spring - Open Pressure 192.72-206.72 @1.177"

400 RA - Automatic Intake Inner - Closed Pressure - 42-48 @1.521"
400 RA - Manual Intake Inner - Closed Pressure - 35-41 @1.521"
Open pressures slightly different just like the outer springs.

Note - The 400 4 bbl with manual trans uses the same valve system as the RA 4-Bbl engine with automatic.

The other versions of the 350 & 400 also show different valve spring pressures and heights.

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Old 12-17-2020, 05:51 AM
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I have these AMA specs too.
Those differences in spring loads on #48 heads are minor and not enough to indicate different springs IMHO, more like an indication of usage of different camshafts, #744 M/T and #068 A/T, with different cam lift at the time of measurement for the AMA specs.

The other heads #62, #47, #46 and #45 have other springs due to usage of #067 or milder camshafts.

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Last edited by Kenth; 12-17-2020 at 06:00 AM.
  #79  
Old 12-17-2020, 07:56 AM
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Quote:
Originally Posted by shermanator2 View Post
I am a little confused by this. Earlier you posted a scan of a parts book showing the springs changing at engine number 709186, presumable corresponding to a cam change from 744 to 068. Are you saying that the #48 heads were used only on one side or the other of this change?
No indication in MPC on that.
But as you noted, this would mean two different #48 heads from factory, one for the #744 cam with the "RamAir" springs and one later #48 heads for the 068 cam with H.O. springs.
That would also mean #48 heads 9795043 sold OTC was w/o valves and springs.
Yes, why not?

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Old 12-17-2020, 11:16 AM
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Sherman let JKrull have the head I had since it appeared like John’s head and our head very well could have came off the same engine. Shenandoah is only 30 miles from were we picked up the 48 we have. So it appears after 40 yrs the heads are back together, if they were off different engines, doesn’t appear you could not get a closer match. But Sherman needs a head again now, hopefully the casting number is posted so he can find a good match. I will keep a look out for a match.

I used the same felpro gasket and scribed a line and it measured .23” on this 48 head. Roughly .050” less than Steelcityfirebirds head. Likely were the extra cc’s are coming from, if it is the same shape I would assume that it has a deeper chamber. The short side of the chamber measured about .14” deep, but it is not easy to measure.

I check a untouch 16 head 72 cc and a untouched 62 75cc head with the same head gasket. The short side of the chamber was roughly .020” deeper on the 16. I had about the same reading on the 62, but the 62 looks like it has a different shape. The distance to the head gasket scribe to the chamber was .11” on the 16 and .080” on the 62.
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