NO WAY was the Norris car anywhere near 800bhp, no more than just over 600bhp. They always claimed 615bhp, and seeing as it had a TD05 25G on it, that makes sense. And considering the speeds it hit, that sounds accurate.
Timed plenty of cars with sub 700bhp to 200mph+ at Brunters, fuck, been in a 650bhp one at 197.6mph. Timed plenty at sub 600 to well over 180, inc a few FWDs.
Gearing plays a big part. You can have 500bhp, but if you go past peak power by about 150 and it drops off fair sharpish you not hitting much more than that unless you got huge amounts of room.
For the same reason I've been in a FWD road car that hit 165 by the halfway mark at Brunters, but also hit the limiter in top, so that was that.
Full speed and speed at 1.7 miles is VERY different though. Most 200mph+ Supercars cant even hit 180 at Brunters.