I've adapted a Chrysler straight six triple SU HS6 manifold by shortening it and welding it up to the flanges cut from a B30E efi manifold. The carburators came with RH needles which proved too rich. I was thinking of using standard B20 (KN) needles on the logic that B30 is one third bigger than B20 so an extra carburator should have the same needle. Anyone have any exerience with this ? The manifold is a simple one intake tract into 2 ports X 3 with a balance tube between very similar to the separate alloy B18 manifold of old. So far it runs good using a standard B30E exhaust system but needs tuning

Nice work, and should make a very well breathing B20 fly if you can get it right.
OK, let's start with the B20 motor & head itself, before you try to find out whcih carburretion you should go with.
Is the motor stock compression or built with a better bottom end with better psitons & higher compression?
Is the head stock or ported, and bigger valves?
Do you know if the motor can achieve higher rpm's than stock, and a cam that can flow more at high rpm's?

The answer to these questions are very important to which needles to choose. The stock needlse for a B20 (US spec) are SM, not KN, and hte SM are much leaner than the KN, especially at low flow, low rpm's. A well built B20 that can flow the max the stock twin SU HS6 carbs is 175 CFM X 2 = 350 CFM, and RR needles can accomodate a good A/F curve for such a motor, flowing 350 CFM and get 200hp at about 7000 rpm. If you take a B20 and add three SU HS6's, (525 CFM max), then you will need three carbs that cumulatively flow 350 CFM or there abouts. I've yet to see a race built B20 go much farther than 500 CFM, and that was done with EFI.
In answer to the big question, the needles will need to have a much leaner taper than even the SM, but that will be the best place to start. I wouldn't try any needle that is any richer.
When you get the carb's on, place toothpic's in the dashpot holes and go for a drive with the hood off and note the height the pistons advance under load, the higher the rise the better the needle is matched to the flow of the engine, depending on the tune and setting. Note this is straight out of the SU manual circa 1966, which I have a copy to scan for you if you like.
Like Webers, the needle matching in this case is going to be just as tricky as jet selection. You may need to go down one jet size (0.08 dia) and run much leaner needles than are available for the 0.100 jets.
I should also note that when Jaguar went from three SU HS8's on the XKE IL6, to two carbs, the HP went up by 40, and the engine flow improved by about 20%

KN's are the standard B20B needle & work flawlessly in anything with a C cam in it which is B18B, B20B, B30A & B30E.

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

How many inches of water or mercury?

2 x 175 CFM = less than 175 CFM per cylinder on a Volvo twin SU manifold.
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.

"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.

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.

You misunderstand, this is for a stock B30 (not efi).

OK, sorry I mis-understood.
But everything I said still applies. A stock B30 with two SU carbs runs fantastic with RR needles which are about high range rich for a stock B20 (two ranges above the KN), but work very well for a built B20 also. I have done this on a 164 B30 that orig had twin Strombergs.

I still think you'll need either much leaner needles or a much higher flow head and exhaust to make three carbs work well.

Since you've already got it running, do the test as I describe and see how high the pistons lift. If the're only 2/3 of total height on acceleration, lean the needles out.

Yes that's right it's a lynx Manifold for a Chrysler 245 hemi six. The welding isn't pretty but it's air tight and not a bad match to the Volvo ports. I had to replace some studs with HT socket head screws but it bolts up ok. The battery will have to live in the trunk. I'll post more pics when I get it set up on the engine and I'm done fiddling

Good work, you could make that look a lot better if you ever get bored enough to do it. I saw a B30 triple Weber manifold made out of an E49 manifold once & it look like a dogs breakfast, but it looked good inside were it counts. I have a crossflow Falcon triple Weber manifold that I want to fit to my 164. The port holes nearly line up, the Falcon is 5mm shorter from the 1st hole to the 6th, so I'll likely cut it up in to three pieces.

I agree, KN needles are certainly a good place to start.
Can you post some pictures of your manifold?
--
George Downs, Bartlesville, Heart of the USA!

Fascinating.. I never knew such a thing existed for Chrysler cars... but a quick google search turned up a manifold made my Lynx in Sydney.. is that what you started with?

http://www.hotsixes.com/hotsixes/?page_id=7
--
-Matt I ♥ my ♂

That's a slant six manifold.

He's likely started from the 'hemi 6' Triple SU manifold.



http://en.wikipedia.org/wiki/Chrysler_Australian_engine
http://www.valiant.org/valiant/hemi-six.html

This is THE best ever inline 6, there was even a factory Triple 45mm DCOE 265 cube E-49 that made Ford Boss 351 Clevelands seem slow.

I was thinking of using standard B20 (KN) needles

KN or KD (B18B) would be the ones to try first for sure. They all have the same cam & similar head.

I've adapted a Chrysler straight six triple SU HS6 manifold by shortening it and welding it up to the flanges cut from a B30E efi manifold.

Somewhere, a Valiant man is weaping.