CFM rating of 340 hp carb

tenxal

Well Known Member
The '409' 4GC's are great carbs!

Primary throttle bores are 1.562 and secondaries are 1.686. We used to experiment with different 4GC's back in the 70's and they were always quicker and faster than any AFB. They flow in the high 600's for CFM. Cadillac, Buick and Pontiac also used these big 4GC's.
 
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64ss409

Well Known Member
Supporting Member 9
:yup. I re-measured. Al is correct.
For comparison, does anyone have the throttle bore measurements for the 400hp AFB?
 

427John

Well Known Member
The '409' 4GC's are great carbs!

Primary throttle bores are 1.562 and secondaries are 1.686. We used to experiment with different 4GC's back in the 70's and they were always quicker and faster than any AFB. They flow in the high 600's for CFM. Cadillac, Buick and Pontiac also used these big 4GC's.
So they would be found on 390's,401's,and 389's or would it be later larger engines?And would it also be on olds 394's?Also does the high 600's mean closer to 700?I need to know if I want add these to my wrecking yard/swap meet list.
 

64ss409

Well Known Member
Supporting Member 9
It's all in the AMA specs at the GM Heritage Center.

This is from the GM Heritage Center.

Throttle bores
Primary Secondary
RPO L31 1.625 1.6875 340hp Rochester
RPO L33 1.56 1.68 400hp AFB
RPO L80 1.5625 1.6875 425hp 2-AFB


Venturi diameter
Primary Secondary
RPO L31 1.34 1.5625 340hp Rochester
RPO L33 1.3125 1.4688 400 hp AFB
RPO L80 1.25 1.5625 425hp 2-AFB
 
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