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"KN's are the standard B20B needle & work flawlessly in anything with a C cam in it which is B18B, B20B, B30A & B30E."
Maybe in the Canadian and Austrailian markets, but in the US it was SM needles and B cam in the SU carbed B18B and the B20B was only in '68 122S and no other US cars, and all other B20B's had either Stromberg or HIF6 carbs. Again, the US cars were set up very low flow and leaner than other markets
the stock twin SU HS6 carbs is 175 CFM X 2 = 350 CFM
How many inches of water or mercury?
It doesn't really matter, total flow is toal flow from the SU rated at 175 cfm. When the engine reaches minimum pressure (In Hg under load) the carb body will limit how much flow is possible. It doesn't matter if it's 15 in Hg or 18 in Hg, the difference is minimal, as velocity is restircted, the flow cannot increase.
"2 x 175 CFM = less than 175 CFM per cylinder on a Volvo twin SU manifold."
Most of the B20 manifolds will flow 125 CFM on a good day, with good tune, stock engine. These are the alium B18 & B18/B20 cast iron manifolds with the secondary throttle valves. The '72 cast iron manifold without secondary throttle plates and no mixing chamber will flow over 200 cfm. I've run a B20 with SU HS6 carbs and modified intake to 350 CFM in such a set-up.
"3 x 175 CFM is pretty close to 175CFM per cylinder on a triple SU on cylinder 1, 2, 5 & 6. On the centre cylinders it does = 175 CFM"
This doesn't make any sense. Six times 175 CFM = 1050, 3 X 175 SU max flow is 1/2 of that. It doesn't add up.
It is not possible to flow 1050 CFM from a 3 liter 6 cyl engine, even if it was the orig slant six Chrysler hemi. You cannot exceed the 3 x 175 cfm per carburetter using SU's.
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