Stock exhaust manifolds when and why . . .

[opelitis1]

Why and when did GM switch from individual exhaust manifold runners, e.g. where the manifold runners connect to the head to a, I believe it is called a "log" type unit, meaning the runners are connected at the top.  Again, why and when did they do this? Even headers are connected.
Sorry if I haven't explained me self correctly, but mebbe someone can wade through my dribble?
Thanks!
Ted

[JohnZ]

All '57-up small-block factory cast exhaust manifolds (the "ram's horn" type used on full-size cars and Corvettes and the low type used on Camaro/Nova/Chevelle) have individual cast-in runners at the head interface that blend together before the outlet. The only ones that were a "log" manifold where exhaust gases dumped directly into a common chamber with no individual runner shapes feeding it were used on '55 to early '56.

[opelitis1]

Good morning John!!  I have BBC exhaust manifolds w/part numbers 3994045 LH side  and 353030 RH side that have reinforcing bars between the ports of the exhaust manifolds.  They look somewhat the same as the 67 - 69  exhaust manifolds 3916178 and 3909879 that do not have the reinforcing links.
   Any idea of what my 3994045 and 353030 manifolds were used on with the "links". There are 2 sets,  - 1 with AIR fittings and the other without A.I.R. fittings.
   Question begs, when and why did GM start to use these links  between the manifold ports??
 Seems to me we are becoming more 'n more ladled with bad information from the various Internet sites as people are a Copying and a Pasting to their heart's content w/o checking info validity..
Thanks in advance!
T.

[Sauron327]

Searching different sites referencing those numbers will reveal the data regarding years used concur. So I won't copy and paste it.

[opelitis1]

Sauron, I have gone onto various sites and data is different in many cases making me wonder what is valid and what is not.. 
Question still stands, when did GM put the reinforcing links on the stock cast iron manifolds and why??
T.

[Sauron327]

Which ones? Is Nasty Z/28's info incorrect? It corresponds with 3 other sites. All I did was type in GM part #s. I don't know the exact engineering reasons why it was done.

[opelitis1]

Good afternoon.  Was trying to get some valid info on  two cast iron units - 3994045 and 353030 on Nasty's site.  Which are LH side and which is RH, according to Nasty, they are both the same side..  Something amiss  here, so I trudged out in the recently fallen snow from yesterday, and,  045s are LH side and 030s are right hand side units.
Sometimes, it's the inconsequential l'il things that'll bite yah.
Take a look-see for sbc heads 14014415 and see what you come back with.. What are the chambers supposed to be at?? 58cc 64cc 76cc .
I read somewhere that Mike's tables were in fact last up-dated 12 years ago.
For sure lotsa folks have copied and pasted possible "mal" i.e. bad  info.
T.