Mounting Injection on a Twin SU manifold produces very subpar results. Strange things happen inside Twin SU manifolds that cause poor mixture distribution + mixture robbing from one cylinder to another. Impossible to make ram effect work properly on a Twin SU manifold too because there is such a bad mix of waves happening inside.

If you are going to Injection, use at least the D-Jet manifold which gives one runner per cylinder, a major improvement over the Twin SU manifold.