Based on the head inlet area of 15.5cm^2 the throttle body needs to have a diameter of roughly 45mm, allowing for a 5mm shaft for the butterfly valve.
First throttle body test
Close up detail
After several hours playing around trying to mesh the model, I gave up and dropped a dimension, as 2D runs a are much easier to build and run. Generally the numbers should be ignored, but the flow lines are usually pretty indicative.
CFD Throttle @ 5250rpm - 45deg opening
But there is scope for setting up some runns with varying throttle opening, inlet pressures. Then can develop injector positions to get the best mixing arrangement.