They are not the ultimate arbiter of truth but they do at least give some sort of vague approximation of data (as opposed to down-the-pub willy-waggling bullshit) for those considering an engine conversion.
Full copyright/credit remains with whoever originally posted these online.
There's some more Rover V8 ones with fancy bits at mez.co.uk.
This is apparently a stock 3.9 V8 plot, origin unknown:
Stock & Supercharged 3.9, found on aulro.com:
Stock & Supercharged 3.5 (fuel system unknown), found on aulro.com:
Rover V8 Variants
This is the best resolution I could find:
Given the amount of tuning they're supposedly good for it was hard to find a dyno plot online
AKA The Nissan Skyline 2.6 straight-6 twin-turbo. Included here as I once considered fitting one in the 109 but it was pointed out to me that the 4.6 V8 makes more torque at idle than this does at 5000rpm, if the graphs are to be trusted.