Richard Holdener is going to be engine dyno testing the 4200 next week, in stock and then boosted (turbo) on a stock motor. He posts on youtube nightly when testing.. Should be good to watch

https://www.youtube.com/watch?v=deFsdY3z1yI
NA dyno runs

For enquiring minds, right now the best run is 555hp and 578ft.lbs. That was with a junkyard 4200.