Quote:
Originally Posted by GTO-relic
the early Pontiac SD455 and Buick 455 1970-74 carbs were always listed as 800cfm rating, not 850cfm. Are you saying the later 1975-up carbs flow 850cfm ?
Where's the extra 50cfm come from ?
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After reading all your posts, I just noticed this one, and think I can offer some assistance;
The 1971 Pontiac (except 400/auto & 455-D-port/auto) used the same 750cfm main body casting, but with the lower booster ring removed - which is why they have a small bump in cfm.
The real 850cfm used a totally different main body casting with a larger primary bore;
I believe that this was a Buick casting which I also believe was only used on a couple engines;
There is a pronounced hump in the side wall of the primary bore.
If you have Cliff's book, flip to page #31 - it's shown on the top.
I believe that Pontiac opted to use this "Buick" bowl casting for all their Quadrajets starting with the 1975 model year.
I when I was looking for a picture to add to this post, I found
THIS post elsewhere...