My First attempts at simulating a 998 in a 100+ overbore using a stock 12G202 head using a Swiftune SW5 did not go to smoothly. Unlike a 4V head with direct acting bucket followers you have to remember that the simulation need valve motion, not cam motion. I did not and thus got a great big dip in the low end that is definitely not there in real life
Just as a first attempt I did a bone stock head using flow figures I measured (manifold on) on my own bench as a starting point for the Cd map.
CR is set at 10.3
A Minispares medium intake with a Hif44 and a 100mm non taper stack. Exhaust is a 3-1 small bore with 25 inch primaries 1 1/4 inch end pipes and a 1 3/8 inch centre pipe using a 1 3/4 inch collector ( straight from the Vizard yellow book)
A siamese port head has a lot of junctions and interactions, as a consequence computation takes quite a bit of time. Using my C2D P9300 2.26 Ghz it takes 8.5 hours for a 250 rpm step sweep from 1 to 7K rpm. Compared to a 4v BMW K 1100 head which takes less than an hour for 1- 10k sweeps.
I am slowly getting there. The general curve shape is now more or less akin to what I have been seeing from a sw5 cammed A series.
now for the simulation of a similar engine: As this is a stock head v.s. a ported head with slightly bigger intake valves the top end is a bit flatter and the low end is still a bit unstable. This is probably due to inaccuracies in the current model. However it is always a bit of a guess how much smoothing and damping is applied to the dyno plots so the bottom end might be not as smooth as it is in paper. So not quite there yet but I think EngMod4t can simulate these engines reasonably accurate once you optimise the input data.