Modifying Standard twin Carb Alloy Inlet Manifold

[dgear1984]

Hi,

I have now finished refurbishing my H4's and working out all the brackets and linkages so I have taken my HS2 off my 1275S as I will be reusing the manifold.

I have a 12G2463 manifold which is exactly the same casting as my broken AEG573 one, which I believe was fitted to late cooper S.

The head I have has been ported, I can easily match the manifold to the larger inlet ports by grinding off the lip used to retain the location rings, thats not an issue and the hole centres are a good match to the head.

I was wondering what other mods I should do to it before fitting onto it my H4's? I can polish off all the casting marks easily.

The carb side flange is already at 1.5" but quickly tapers down to 1.25". Im not sure how much I can really open this up as it would leave a rather thin wall thickness on the elbow. I could easily make it more oval as the top part of the taper will only go into the link tube part.

On the head side flange would it be advantageous to radius the back of the flange at the top where there is a square edge into the link tube?

Hope that all makes sense.

Should have really sent the manifold off with the head but there we go, I will see if the guy who did the head can still do the manifold and what he recommends doing but I though I would also ask here incase I end up doing it.

Thanks Dave

[mini63]

vizard's books detail the mods to the twin manifolds.
'Tuning BL's A series Engine' or 'How to Modify your Mini'
basically you're on the right path but matching the carburettors to the manifold to the head is the primary tweak. not so much polishing though.
the other one i can recall is removing and rounding off/smoothing the sharp-ish edge created inside the inlet tract where the balance tube intersects the inlet tract on the engine side - direction of flow.
Also, thinning the butterly spindles and removing the splayed disc screw legs inside the venturis is a nice touch too but a bit old school......

no big horsepower gains to made just tweaks that add to the sweetness of the engine on the road.

[mk1]

As Michael says, Vizards book gives chapter & verse on modifying these manifolds.

Basically it boils down to open everything up so it matches, make sure all transitions are smooth & all edges are radiused.

[dgear1984]

I had a copy of "how to modify your mini" but the version I have didn't really say anything about the inlet manifolds.

Borrowed a copy of the "tuning the a-series", looks like a really good book, Im going to order one.

Got the grinders out and modified the manifold today. The alu is nice and sort so it was easy to work with.

Below is when I had done just one side. Im not sure Vizards "just a few minutes work" was totally correct, took me the best part of all morning to complete the job.

Anyway, thanks for the help.