Well, my 3UR is making 1045WHP and it's 100% open deck. It has some headroom left but it was my daily and 1000hp was my target so we stopped at that. Papadakis' 2AR is open deck (as far as I know and found online) and it's pushing 1007WHP out of a 4 cylinder. (250hp/cylinder or 370hp per liter). I'm pretty confident a modern closed deck inline 6 won't have an issue holding 170hp per cylinder.