[Shiny]

Originally Posted by Formulas

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

I always felt the same way...If there were two versions of the 48s they would've had 2 different #s....the end.

Originally Posted by steve25

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.