I just want to help not step on anyones toes and I can only thank what Sikyne and Jmac with
Simons handy work making manifolds for me and others at his workshop really hitting home.
Just using a separator will make that a T intersection like hitting a wall dead on.
Turbulence will reduce efficiency overall more than 5-10 per cent claimed to around 25%.

With a little rotation and grinding off the 1 and 4 bends the 1 and 4 collection points
meeting the flange will be more angled relieving the T instersection effect.

The other option is the true and tried TOPGEAR manifold which is the ultimate and very little use of material also but ultimate flow.
When I say True is that from 33hp at wheel it improved to 128hp almost 4 times improvement.
Even that manifold could be improved if you look at the picture

A.
types of bends in blue circles can be 1.2,3 and 4 (1 is square, 2,3 bends and 4 straight pipe)

B.
The white arrows are where you can rotate 2 and 3 bends down at that point then number 4
can be a straight pipe and also allow more inlet manifold clearance (indicated in green).

Pieces total excluding flanges: 4 square, 4 bends and 2 straight.

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