23 replies to this topic

[djmini92]

Hi,

I have 2 HS6 carbs which i am thinking of fitting to my 1380cc engine, is this too much for the engine or would twin 1" 1/2's be better (or a single HS6 but would prefer twins)?

Thanks very much in advance.

Djmini92

[Cooperman]

With a really hot cam and high revs, like over 6500 rpm, the twin HS6's would probably be good on a decent inlet manifold.
twin HS4's would also work well. The limitation is not so much the carbs as the horizontal inlet tracts. After all, there is no point in having a carb cross sectional area greater than the inlet tract area. If they are more or less the same the inlet charge velocity will be optimised. Measure the inlet tract area then decide.

[bmcecosse]

Ideal! But don't use a manifold with a 'balance tube' - use a short straight tube manifold for each carb . Set up properly these will beat a 45DCOE - and no need for a box sticking in to the dash area.

[Shifty]

HIF44 would be my choice.

[1275GTS]

I run twin HS6's on my 1330 with lots of other mods. These have been set up properly on a rolling road and work very well.

[Ivor Badger]

Set up properly these will beat a 45DCOE

A common misconception, by those that haven't tried it............

I have tried both assisted by bmceccosse. So he does has effectively tried it.

[Gulfclubby]

A HS6 has the same internal diameter as a HiF44, so the performance difference should be next to zero.

[Cooperman]

The Weber range of carbs is probably the finest ever designed for production. A properly set-up 40DCOE, or 45DCOE on a full race engine, will almost certainly out-perform the equivalent pair of SU's. That assumes that the Weber is not mounted on one of those awful Swan-neck manifolds.
Once set-up the Weber will be a very stable carb requiring little adjustment.
How much actual difference you would see is another matter. If racing you would see a second or so per lap, depending on the circuit, but on the road and in practice very little difference.
On a 'back-to-back' test by Mini World on several rally Minis a few years ago there was no measureable difference on a twisty handling test between those with Webers and those with H4's or HS4's.
It's really a matter of taste and personal preference really and whether you want to do the modification to the bulkhead.

[AndyMiniMad.]

Im runing an Hiff44 on my 1380 and my mate runs a 45 webber...On the rolling road his 1380 produced 112bhp and mine 98bhp..So a considerable increase in power. Both engine specs are more or less identical. But on the open road the extra horse power is not a huge advantage and its pretty much 50/50 on who wins the sprints on the twistys...But his sounds bloody brilliant under load.

[Gulfclubby]

Well, that doesn't really tell us anything. The bore size is not the only factor for increased power. Are you both running exactly the same engine otherwise?

[AndyMiniMad.]

Sorry, yes the engine specs are the same....other than his car runs a pre-verto clutch and mine is verto...I know that no two engines will be the same so Im not saying all the extra power is coming from the carb...I was simply making the point that even with the extra power, the actual difference when driving is very small...

If the OP is building a track car or a drag strip, timed quater mile type car then yes the extra power is all important. But in every day use...im not so sure...

[bmcecosse]

The disadvantage of the 45 DCOE is the internal secondary choke - and the limited main choke size - both limiting ultimate flow. Also - the pitch of the two chokes does not correspond to the pitch of the A series inlet ports, so the manifold has to have an S bend.... Twin HS6 (or HIF44) have virtually no internal disruption to the flow when on full throttle - and can be mounted dead in line with the head inlet ports ensuring best possible flow. Ivor Badger's car was better on the HS6 carbs - and won the Scottish Saloon Car Championship that year - beating others who had obviously spent VERY much more money on their cars and engines........

[Cooperman]

Unless you are wanting the ultimate 2 or 3 extra bhp it's really down to personal choice.
The real ultimate in carbs is probably the old 'split Weber' set-up where a pair of Webers each had one half cut off to leave one choke for each carb. This was then welded to an adaptor plate and bolted to a 'standard' (if you like) BMC inlet manifold. This met, just, the homologation requirements where the original inlet manifold had to be used, but the carbs were free so long as they bolted directly onto that manifold without any 'intermediary device'. The engineers at BMC had thus created a prototype carb which bolted straight on to the manifold. They worked very well and gained a couple of bhp or so,

[bmcecosse]

I know 'Ivor' tried split Webers at one point - but not sure if it was at this time..... I'm sure he will be back to tell us! But yes - all this is for the very last couple of BHP and probably not all that important for anything other than out and out competition use.

[Cooperman]

A few years ago there was a test day and Peter Horsborough was there with his Cooper 'S'. At that time it had a 649 cam, 45DCOE Weber and an LSD set not-too-tight. It was very quick on a standing start straight line drag, but on the handling course, Peter was about 2 seconds quicker when he drove my car, (286, twin H4's, x-pin diff, etc), than when he drove his, and I was much slower in his car than in my own. He then had his engine altered to exactly the spec of mine and said that overall he was much more competitive on rallies with 'my spec' engine. In fact on our next event he won and I was a close second.
Out-and-out racing is quite different, of course, and a few bhp can mean the difference between winning and coming well down the field.