There’s been a few past 1000hp now, probably the most well known is the ag focus, engine built by harvey Gibbs, it made 989hp on engine dyno and 1000+ on rolling road. Properly takes abuse on track too and has run low 9’s at Elvington on a damp track.
it would be good too see what a big capacity one would do, as I’m sure it’s possible too go to 2.7 litre with the smith and jones block.