SU carb question - needle size calculation?

[murcod]

Does anyone know how to "guesstimate" what needle size a 3.3l engine might need with a single HS6 1.75" SU?

I know there would be a lot more info needed to be accurate, but my current dilemma is the engine in my 2.5 PI is a Holden 3.3l (202ci) 6 cylinder. It's got a single HS6 (I know undersize for the capacity) and it's running like a pig. The fitted needle appears to be modified with a drill/ wet and dry - there isn't a visible needle size on it.

I've searched high and low but can't find any similar size engine running a single SU.

[Alec]

Hello David,

all I can suggest is have a look at this programme:- http://www.winsu.co.uk/
If you scroll to the bottom of the page you can download a free copy of the software.
The needle you have will be identified on the shank, I can't imagine why modifying it should have obliterated that? (not that it is relevant anyway if it has been modified)

Good luck

Alec

[beaver]

Hi david,

As a fellow downunder'er (Im in NZ) I know of the holden 202ci engine well.

Why dont you try track down an original manifold and carb for it (stromburg or varijet) rather then using an inadequate sized SU?

cheers

[murcod]

Hi Alec, I don't why the number/ code is missing, but there's nothing on it. It has also been soldered into the biasing base which is the reason I think it has been modified. It wouldn't surprise me if the previous owner made the needle up from a piece of brass rod. He's made his own single SU inlet manifold to suit the 202 engine!

I've had a look at that program and couldn't find much of use in it (unless I missed something?) You need to tell it the manufacturer and car model before it will give you a needle- needless to say Holden doesn't rate a mention in there. I also couldn't find a similar capacity engine listed that's running a single HS6.

Hi Beaver, I need to stick with a side draught style carby. There isn't the height under the bonnet to fit a standard 202 inlet manifold and carby. I've been watching out on Ebay for twin SU manifolds but they're selling for ridiculous prices (eg. one last week for $600 with carbys, I did miss one the other day that went for $305 ) There are triple SU manifolds around but they sell for even more and I'd have to relocate the battery to fit them.

[tony]

Got a feeling that a single HS 6 is not big enough to fuel a 202. How about a 2 inch (Jag ?) S U ? How big are the manifold ports?
Cheers Tony.

[Alec]

Hello David,

what sort of power does this engine develop? (As standard)

You can fit a 2" S.U. on that manifold as the flange mounting is the same, but the manifold would need opening out, however I do think that your existing carburettor will work. (For example my 3 litre Ford V6 engine of 150bhp runs on a two choke Weber, nominally 38 mm chokes but the venturi are only 26mm so similar to 2 x 1" S.U.'s so one 1 3\4" should fuel your engine?)

The 6 series needle dimensions are quoted as 14 steps of 1\8" with the start position nearest the shank being generally 0.99". It is going to take some work but if you can measure the existing needle and work out where it is wrong , using the S.U. chart to select a needle nearer what you require.
There is another site that does a needle comparison:-http://www.mintylamb.co.uk/suneedle/

If you click on the original needle box, it will give a drop down menu so select any one to give you a basis to start. If you would like to let me have an e-mail address, I can scan the S.U. book that explains selecting an alternative needle and send that to you.

Alec