I have an A14 in a Triumph Spitfire. There's about 4mm of clearance between the oil filler cap and the hood. This means there's a big hole in the hood to fit the downdraft carb.
I designed and 3D printed two intake manifolds out of PLA to adapt an A14 to a pair of sidedraft SU carburettors, coated the 3D prints in a plaster of paris/sand mix, burnt them out in an oven, and cast them in aluminum, then sawed the casting into its separate pieces and milled the mounting faces of the intake manifolds flat and parallel (and the same height.)
There were a number of issues: one bit of the mold didn't fill so I had to weld it up, the way I made the 3D print with switchable plates to fit the two differently-handed carbs ended up leaving weird divots on the inside of the casting, and the top face of the castings don't have the detail I'd like, plus just pouring the plaster over the surface meant there were big air bubbles on the bottom sides of the top plates.
However, they slip right on the A14, they'll seal well, and they fit the SU's.

I also designed them with fuel injector bosses so if I want to go down that route I have a good start. (In the long term I'll get a Hayabusa throttle body set and cast another pair of these with diverging rather than converging ducts to fit the Haya spacing.)
I hope the included pictures come through okay.

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I thought of using a side feeder for the oil cap on the tin rocker cover
basically to make it easier to never spill oil on the engine and aesthetically
would make the engine look longer with the fully top smooth rover cover etc.

Matt made some awesome billet rocker covers that you can flip the top off
and access all the hardware and fill with oil etc. in billet alloy.

wow those look great

I wonder what the performance difference will be without the standard SU-style balance tube connecting the runners

I did a previous model of these that had a pad on top for a balance tube. If these are trouble, there's a point where there's enough metal thickness that I could tap in a pipe fitting and connect them with a hose. I'm hoping that it'll do okay without.

maybe something to do with the flat plane crank pulses
not experienced in other SU engines that are not L4.

right all fours all flat-plane cranks. The weber book says it has to do with the number of cylinders not specifically the firing order. On a four-stroke engine 2 cylinders per carb means the carb is only being used 1/2 the time. Which is why twin webers don't make more substantially HP than a single on a four cylinder. The single uses a plenum to allow all four cylinders to draw effectively using the single carb constantly. On the other hand twin webers can use tuned ports to gain the advantage. But few twin-weber manifold are long enough for that

The other question is about smoothing out the vacuum, which is irrelevant at full throttle

Not many engines can have flat plane cranks by the looks of it
only L4 and v8 engines but not v12 as they act like an L6
The balancing tube should cancel out any reversion that could
interfere with the setup but will be interesting to see results.

For webers single or doubles the manifolds are not optimum
for all applications where different lengths could improve
those after street tunes but most weber manis are designed
to fit into the engine bay.

However by tinkering I found the longer than length of the
runners the fatter torque that I could get for the street.
I used to make my own quad cv carb manifolds of varying lengths
and the longer I made them thanks to 1000 having good space
for them the better response I had everywhere.

I'd love to have longer runners on the intake, but there simply isn't anywhere to put them. I thought about doing something similar to the BMW 2002tii setup, with intake runners that sweep up 90 degrees, then bolt to a manifold of runners that go over the top of the valve cover and put the fuel system on the other side of the engine. I'd love that, as I have a lot of room over there and could some day fit a supercharger under it. But to get the airflow in the space I have, I'd need to cast elliptical tubes only about 22mm high and really wide. I'm still thinking about it. But mild supercharging and fuel injection seems to be a lot easier.

BTW historically fours had a weight and power advantage because a flat-plane crank could be forged rather than cast, so had a really good strength-weight ratio. These days industry can handle multi-axis forging, so that's no longer such a big deal.

What's so difficult about making long runners?







this one looks complicated