Fabricating a Weber Carburettor Manifold Flange

Hello dear learned colleagues,

I am planning on fitting a Supercharger to my classic Mini A Series Engine (lots of people

have done this).

There are of course complete kits that you can buy but I, like many others, are going to try the DIY route.

To mount the Weber Carb onto the end of the SC, you need to cut the SC with a bandsaw and weld on a pre fabricated flange like this, as shown in this video at about 11:07.

Watching the video I have seen that, to reduce the amount of weld filling required, the flange shape needs modifying, as it is too small across the top.

So here are my options:

a. Try and draw the flange in 3D package and get it CNC’d or

b. Try and mill it myself

Problems, I don’t have any dimensions (I do however have the carburettor which I could use to get them?
I have a Warco Hobby lathe which I have adapted for milling with a vertical milling slide.

So a little searching on the Interweb and I found the dimensions, but then also found a CAD engineering file.

i can register and download it, but not sure what the file format would be to add the infill that I would need?

https://grabcad.com/library/pinto-weber-dcoe-intake-manifold-1

Edited By William Harvey 1 on 19/01/2022 22:18:52

I have a Warco Hobby lathe which I have adapted for milling with a vertical milling slide

Can be done, I expect.

Report back how you get on? Personally I would prefer to use my mill(s) for this, but carry on. Good luck.

Does it even need that much if any machining.

Two large holes can be done with a holesaw or you could clamp to your vertical slide and bore on the lathe, I'm assuming its too big to swing.

4 smaller holes are just drilled and tapped.

Then hacksaw the main shape and file the rounded bits which would be quicker than trying to set it all up on a vertical slide,

Or Weld a block of aluminium to it where it is too small then dress flush and do the other welding. Something like the bit of plate shown in red with some deep weld prep to the green edges. Clean it all up and then weld it on as one with a lot less heat going into the job

Don't trust those sizes.

Edited By JasonB on 20/01/2022 09:02:48

As Jason says you can whittle that just as easily with hand tools and drawing around a card gasket.

Side draft Webers were not a popular swap for minis back in the day due to the need to cut the firewall. Inserting a Merc blower in there at least fixes the issue of the carb trying to swallow the speedo.

However why the u-tuber strangles the air flow into the blower so much with all that weld instead of lifting the carb plate up an inch and use all of the slot + the unequal length outlet ports from the plenum. Mind you he does say the kit that he sells is different so maybe you are supposed to try DIY then give up and buy from the 'expert'.

Says he off sets it downwards and skims the bottom of the blower so it will fit under the bonnet.

So why not use a chunk of 40mm thick alloy and angle the ports down 45deg to drop carb or leave the blower un cut and use an SU on a 90 elbow and block the other blower port with a plate? Though that might put the hydraulics in the way.

My visualisation of mini bonnet space is of course now 50years old

Hmm. Don’t underestimate the project. I started off making a manifold then got Maniflow in Salisbury to do it. It’s tight in there….

That aside. I used 10mm plate and cut it with a hole saw in a dewalt battery drill I have more better tools now! The sectioned steel tube bought from EBay.

MInes a 69mini with a Shorrock Btw

Rather than using a DCOE sidedraught (as has been pointed out the way to fit these in the '60's was to replace the speedo binnacle with a battery box welded into its place), why not use a DCNA downdraught with a suitable manifold? then fit the supercharger to 'Blow down' the DCNA - far better transient performance from a blow down set up, but you'll need a pressure sensitive fuel regulator. The problem with 'suck through' forced induction systems is the lag time and in external compression superchargers 'bearing wash out' from excess fuel and in internal compression 'centrifugal chargers' the fuel gets 'centrifuged out' causing major driveability issues.

Then of course you will need to do something about the idler drop gear (between the Deva gear and the gearbox 1st motion shaft), high torque and power will destroy the standard needle roller - even with a steel top hat bush insert supporting the gearbox side bearing, the way to strengthen these bearings is to do what ST at Abingdon did and utilise a TR bearing assembly with the gear forming the cone side of the TR. The Turbo Metro had to have a torque limiting system which reduced power below 4000 rpm to protect the gearbox warranty!

Martin

I’m about ready to fire up. But they bottom hose is leaking and that entails pulling a lot of stuff back out again… belts off, fans off, manifolds off and charger back out. It’s a full days work..

Ask, and you shall receive. DCOE flanges in aluminium £25 from the Bay of Fleas....

https://www.ebay.co.uk/itm/334223741773?hash=item4dd149934d:g:rgQAAOSwKIpWFPuM

Will do

That's what I was thinking, But I've never welded aluminium before and not sure about two grades of aluminium, although that would be the same issue when welding the flange to the supercharger? Adding the plate would, like you say reduce the amount of welding and ergo the possibility of overheating the bearings.

Yes as Jason B mentioned, the reason he sets it 14mm below the top of the SC is for bonnet clearance, but it would restrict air flow?

Here's the SC I have. It's an Eaton M65 from a Mercedes SLK.

Here's the Weber (I obviously won't be using the manifold).

So you are suggesting make a wider flange that is angled downwards to (a) mount the carb lower and (b) maximise the port size.

Like this (crude attempt)

Edited By William Harvey 1 on 21/01/2022 14:41:58

That would certainly give a smoother flow due to the longer transition from the Weber shape to the SC, ideally you would do a lot more shaping of the 40mm block. if you draw each have on either side of the block and then use the loft function of the CAD package that would give an idea. Assuming the extra 30mm does not put the intake end of the carb in the way of anything

Edited By JasonB on 21/01/2022 15:43:56

I think I would go with Dave Halfords idea of an SU, simpler, less work and if it's not so good will have cost little . why use a double barrel on a blower rather than a large single choke ? All an interesting project ! Noel.

Sorry which side would go towards the carb?

What’s the loft function?

The two holes are the carb side the oval would match the blower intake shape essentially like your existing manifold only dropping the carb height and except the blower end would be a single oval port.

Can I suggest that as you haven't cut the blower yet and IF there's room, that you try fit an 90deg elbow on the pipe flange (and a blanking plate on the other hole if it fits) your existing SU will do for size.

The reason is SU's are known to work well on blowers and there's a lot less trouble with jetting (you can get a Gunson Colortune to check the mixture is in the ballpark. Some of them even had electric heaters to combat the icing.