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triple HS6 SU - needles ? 140-160

uid 37336's pic
posted by  B20Paul. on  Tue Jun 16 03:34 CST 2009
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last visit: Mon Oct 20 10:54 CST 2014
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in the US it was SM needles and B cam in the SU carbed B18B

That would make it a B18D. B18Bs only have C cams, B18D's have A or B cams.

the stock twin SU HS6 carbs is 175 CFM X 2 = 350 CFM

The balance tube on Volvo Twin SU manifolds does not act as a plenum. The rear pair of cylinders are unable to receive any meaningful flow from the front carb & vice versa, that's why 2 x HS6 is only the same flow to the head as 1 x HS6.

"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.

Again, the balance tube is not a plenum.

How many inches of water or mercury?
It doesn't really matter, total flow is total 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

175CFM@15"Hg=192CFM@18"Hg. Carburettors flow figures are given at 3" or 1.5"Hg, So if you are saying 175CFM@15"Hg, that's 55CFM@1.5"Hg.





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