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Old 12-11-2020, 05:54 PM
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Quote:
Originally Posted by Formulas View Post
All you have to do is work in a massive production environment to realise that the smallest minute change in any part drives a part number change an identifier s....
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Originally Posted by gtospieg View Post
I always felt the same way...If there were two versions of the 48s they would've had 2 different #s....the end.
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Originally Posted by steve25 View Post
That's not the case since we have D port number 16 castings with the long exh air injection passage running above the Exh ports and without it, and you would have thought that with such a big change in the casting that the factory would have assigned a different casting number, but they did not.

The best explanation I have ever heard is that a certain number of 66 CC casting 48 heads went thru a abbreviated maching process of the chamber to get leave it at 66 CCs and not 72 , and these where to be used on the 350 HO option coming up in 69 that Pontiac had high hopes for sales wise.

When those big sales numbers did not come to pass then these heads where used on the manual transmission RAlll motors only!
Please forgive my rambling here but this thread snagged my attention...

I agree the engineering documentation for these heads would settle the argument. These docs don't seem to exist.

My experience in other industries is in line with a need to be able to trace and/or identify any "unique" part.

Whether for repair/replacement or for warranty tracking, I think the difference between 66cc and 72cc is big enough to warrant a unique identifier if both versions existed. Unless they could be swapped without affecting anything, I would consider them "unique". The "premise" that a 350 needed a smaller chamber than a 400 is the support. If you could swap a single head with either chamber volume on either engine without affecting performance, then there was nothing unique and no reason to ever make both versions.

IMO, a "unique" identifier could be a combination of date code and casting number or a unique casting number. I doubt it, though, as a dealer replacing the head would have to be able to order either version. I cannot imagine GM's parts system could manage the same casting number with 2 different chamber volumes unless they had different part numbers.

As to the same 16 casting having differences, that does not seem unexpected IF the differences did not matter in any supported application. In the case of the 16 heads, could either be used in any application? If not, then how did a dealer identify which was which? How did a parts person order the right head?

Net:

1) did GM/Pontiac have part numbers that supported unique parts with the same labeling? If so, how was that part number "traceable" on a head? If they relied only on dates, that might make sense but puts a lot of faith on the parts people knowing what to look for...

2) could a single 72cc head be on a 350 or 400 with a 66cc head and not matter? If so, then they are not "unique" and I can see how both could have existed for some weird reason...

I don't know how the GM quality management system handled field failures and field returns, but without a "traceable" part number, seems like it would have been total chaos and an unacceptable business risk in event they shipped bad parts and started seeing the impact on their warranty costs.

  #22  
Old 12-11-2020, 06:00 PM
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I will look for that 48 head I have and get another chamber cc measurement, and have a look at the date code. I know I flowed tested it and have flow numbers from it, but I could very easily be getting the chamber cc’s confused with 16’s I have checked.

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Old 12-11-2020, 10:30 PM
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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.
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  #24  
Old 12-11-2020, 11:00 PM
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Jay, can you send me some pictures of this head?

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Old 12-12-2020, 12:17 AM
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Dan Whitmore was specific about this. He cced heads right as they came of factory engines. He was a dealer mechanic and did this because he was meticulous. He wanted to know and found out. The man forgot more about PMD iron than all you put together.

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Old 12-12-2020, 07:09 AM
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Steelcity, would you be willing to do this?

1) measure the depth of the chamber on the shallow side .

2) use a black marker or whatever and color up the deck surface on the plug side around the chamber, the set a head gasket on it and scribe a line that enough to be seen when you remove the gasket, take for use a picture and post it up here.

Thanks in advance if you can do this for us!

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Old 12-12-2020, 07:35 AM
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Quote:
I also notice a X stamped on the head above the 4 on a head boss.

That's great.
There is a thread on these heads somewhere. It was never decided that there was a separate marking on them. This is the 1st example that I have seen.
(except would have thought the 350 HO head would be marked)


Post more on this, please. Also have the pair?



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  #28  
Old 12-12-2020, 08:52 AM
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Rocky I will clean it up later today and send you photos.

I will put some better photos on the forum too.

John we only have the one 48 head. I never knew any history from the head, we bought close to 20 years ago from a local guy when we went to look at his 76 Black 455 T/A. Looking at the head it was ran very little. There is no electrolysis on the head surface and the valve seats and valve guide seem new. I am curious what the head has for stock valve springs, and whether the springs were for a 744 cam or a 068, the spring coils looked a little bigger than a typical poncho head. I will clean the head up an check for more identifications.


Last edited by Jay S; 12-12-2020 at 08:55 AM. Reason: Edit
  #29  
Old 12-12-2020, 12:13 PM
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#744 cam got #9794934 and #9794939 springs. 124lb@1,586".
#068 cam got #9781476 and #9779009 springs. 115lb@1,586".
#067 and milder cams got #9779008 and #9779009 springs. 100lb@1,586".

Bying new springs for all #48 equipped heads thru eng.-#709185 you´ve got the #9794934 and #9794939 #744 Ram Air springs.
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  #30  
Old 12-12-2020, 12:31 PM
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All the 48 heads we've seen with the original valve springs had very stout springs agreeing with Kenth's statement. They were around 125 seat and over 300 near coil bind. They wouldn't handle much more than .450 lift. All those heads measured around 66 cc and came off 400 engines.
I'm thinking maybe the combustion chamber design changed when the 068 replaced the 744.

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  #31  
Old 12-12-2020, 04:43 PM
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I have a set prepared by Jim Robertson, he's probably had more set of these accross his bench than anyone lol.
Were were after max compression for an iron headed 400 build, (as close to 14 as we could get).
If you look at the pics posted with a head gasket ring, vs a typical 72cc head, you will notice a difference. Short turn also.
Can't measure mine as the are on an engine at present, and we're Mill 0.080" so no longer original, but they certainly started out alot less than 72cc

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Old 12-12-2020, 04:46 PM
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I have a set prepared by Jim Robertson, he's probably had more set of these accross his bench than anyone lol.
We were after max compression for an iron headed 400 build, (as close to 14 as we could get).
If you look at the pics posted with a head gasket ring, vs a typical 72cc head, you will notice a difference. Short turn also.
Can't measure mine as the are on an engine at present, and we're Milled around or over 0.080" so no longer original, but they certainly started out alot less than 72cc.
From memory the ended up around 50cc.
I will try and dig out some pics

Formulas, you might want to check with your dog again..........
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Last edited by 455-4+1; 12-12-2020 at 04:53 PM.
  #33  
Old 12-13-2020, 12:29 AM
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Quote:
Originally Posted by steve25 View Post
Steelcity, would you be willing to do this?

1) measure the depth of the chamber on the shallow side .

2) use a black marker or whatever and color up the deck surface on the plug side around the chamber, the set a head gasket on it and scribe a line that enough to be seen when you remove the gasket, take for use a picture and post it up here.

Thanks in advance if you can do this for us!

I will get measurements for you, as I am curious as well.

  #34  
Old 12-13-2020, 01:49 AM
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The later production head I have here appears to have a slightly bigger combustion chamber than 455-4+1. Look at the flat area from the spark plug to the edge of the chamfer at where the machining ends, the head I have is a little wider there. The edge of the chamber looks like it is out further on the head I have. The pic with the marks is the 455-4+1 head.

I cc’d it after I cleaned the head up better and it was 70cc. Lost about 1 cc from what I did earlier, still always to go to get to 66 cc.
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Last edited by Jay S; 12-13-2020 at 02:14 AM. Reason: Type
  #35  
Old 12-13-2020, 02:10 AM
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A couple more photos. The OP wants the head, and wanted to clean it up himself. So here it is in all it’s glory. Looking closer I think I put that valve spring on to hold that valve shut back when I flowed the head, OEM springs are long gone. I do not see anything unusual other than that little X. Rocky thought since it was a late date it might have the same chamber as a 12. Similar to what Paul K mentioned.
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  #36  
Old 12-13-2020, 07:08 AM
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Dan Whitmore could have only experienced a small percentage of 9578 RA3 motors that rolled out of the factory in 69 with the 48 casting bolted on them!

Out of that number there where 2099 motors that came with a TB400 bolted up behind them, and it's my contention that a really good number of those motors produced got the 72 CC version of the 48 castings.

Dans blanket statement with the small percentage of motors that he came across is obscurd to me , sorry!

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Last edited by steve25; 12-13-2020 at 07:14 AM.
  #37  
Old 12-13-2020, 08:07 AM
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Contentions w/o evidence is worthless.
I would like to see one set of 66cc #48 heads beside a set of 72cc #48 heads.
I dare to say this will never happen.

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  #38  
Old 12-13-2020, 08:10 AM
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Quote:
Originally Posted by Jay S View Post
A couple more photos. The OP wants the head, and wanted to clean it up himself. So here it is in all it’s glory. Looking closer I think I put that valve spring on to hold that valve shut back when I flowed the head, OEM springs are long gone. I do not see anything unusual other than that little X. Rocky thought since it was a late date it might have the same chamber as a 12. Similar to what Paul K mentioned.
If they are the same as #12 heads they would be 66cc.
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  #39  
Old 12-13-2020, 09:05 AM
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I dont need to re'check a flippin thing iam not contesting cc's iam contesting identification of a part with 2 different distinct qualities and 1 part number / identification.

The guy who rough cast the head didn't walk over to the machining area with a mythical 350 #48 head let's cut this one different then walk over to the engine assy line. hey wheres the 350 HO blocks and put them on.

There is a numerous amount of custody changes of parts in a assembly line people going home changing shifts weekends or just flat out I did my little part to a widget and pass it to the next operation

Every step somebody grabs the new part they would be derelict in not mentally checking do I have the right part am I doing the right thing

1969 assembly lines were not highly automated and if they were guess what there would have to be a ID to trigger the machine to treat a part differently than another whether cutting a chamber or setting a particular head on a short block

I have had my own set of #48's for 38 years so I have also wondered and paid attention to the unfounded wives tale

You all can cc #48 heads all you want come up with 30' cc or 100 cc i dont care have fun there will be variations within build tolerances and post production maintenance doesn't prove there is a 350 dedicated and 400 dedicated head with the exact same components with the exception of intentional chamber sizing all with the same final assy part number

Or else you would have 400s with 350 48 heads and 350 with 400 48 heads

When somebody or a machine drops the head on a short block they have to know 1 very important thing is this the right head for this block period

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Last edited by Formulas; 12-13-2020 at 09:15 AM.
  #40  
Old 12-13-2020, 10:13 AM
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It would make sense the 66cc 48 heads may have been originally intended for the 350 engines and somehow ended up on the 400's. It makes no sense they wanted a d-port 400 to have more compression than the top dog RAIV engine.

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