8 replies to this topic

[HUBBA.HUBBA]

Can someone explain what their purpose is?

[nicklouse]

Same as twin SUs. Supposedly give a better shot of fuel to the engine.  But longer manifolds on a 45 give the same if not better results.

 

now it mainly comes down to race rules and regs. I swapped out a pair for an IDA.

[imack]

The barrels of a single dcoe weber are closer together than the two inlet ports in the cylinder head so the air/fuel mix doesn't take a straight run to the intake ports so the outer two cylinders tend to be rich and the inner two run slightly lean. Long single dcoe manifolds reduce the mixture difference but don't completely cure it.
Split Webers use one barrel of each carb and perfectly align it with the intake ports to give even fuel distribution between all cylinders like twin SU's as Nick mentioned.

[Spider]

Pretty much as Nick mentioned. A Single Weber, particularly for street use, tends to run cylinders 1 & 4 Rich and 2 & 3 Lean. Running Splits allows each Barrel to be centred over the port and gives better fuel distribution. For Competition use, this is almost academic.
 

<Edit: Imack beat me to it ! >

 

The Factory Works Team used them for some events back in the 60's where the rules dictated that Carbs were free to be changed, however, the Standard Inlet Manifold had to be retained. It gave them a means of fitting Weber Carbs.

Edited by Moke Spider, 17 January 2020 - 07:13 PM.

[imack]

I'd love a set of splits, if only for their looks.

[Cooperman]

The idea of split Webers came from the old Group 2 rules, which stated that the carbs were free, but that they had to fit onto the original inlet manifold without any intermediary device. For the Cooper 'S' that was the old alloy twin carb one onto which the 'works' fitted twin H4's.

 

So Longbridge took two Weber 40 DCOE's and cut them in half to give a pair of 'split Webers. However, they would not fit onto the manifold without a special spacer . With this in mind, a flange was designed and welded onto the Webers and a drawing made with a proper BMC part number.

 

At scrutineering for the next rally, it was suggested that these were illegal because they had an 'intermediary device' - the flange.

 

BMC pointed out that this was a prototype carb and the flange was an integral part of the 'Carburettor -Competition' which had a BMC part number. It was fitted directly onto the production manifold and there were no intermediary devices. It was deemed to comply with the FIA Group 2 rules

 

Those were the days before this was known as 'thinking outside the box'.

[OzOAP]

[HUBBA.HUBBA]

Very interesting. What prompted me to ask was seeing the pair of split webers from MED and I couldn't realise the difference between a pair of splits and a normal single weber. Seemed like a lot of effort and waste.

Edited by HUBBA.HUBBA, 21 January 2020 - 11:22 AM.

[Cooperman]

Apparently the idea of a Weber on a  Cooper 'S' came after triple 40-DCOE Webers were fitted to the rally Healey 3000 and a good increase in top end power was achieved.

The ideal was a single 40 DCOE on a Cooper 'S', but that could not be done on the standard allow inlet manifold, even with a special flange arrangement, so they simply cut a 40 DCOE into two pieces to try it and with the flange welded on to the two halves it met the Group 2 regs. I don't have any figures for the power gains, but they were a more reliable carb than the SU once set up with the right jets.

Personally I have never used a pair as my rally 'S' has twin H4's and my 1990 Cooper will have a pair of HS4's when I get around to re-building them and fitting them.