I watched those and the videos on turbos and variable geometry turbos, very interesting . The stuff about exhaust manifold pressure kind of went over my head lol, but I can see how the twin scroll is designed to spool up faster at lower revs.
So it looks like a variable geometry turbo is best in terms of the overall boost, and the twin scroll reduces lag at the expense of high-RPM boost, is that correct?
Pretty much.. but what that video fails to mention is vgt are only really viable on desiels, as its crazy expensive to make vgt for petrol cars due to higher exhaust gas temps, which damages the vanes. Hence the use of conventional, twin scroll or sequential turbos (later being giving good spool times and higher rpm boost) being the main the stay on petrol engines. Porsche for example has used them, but £2,000+ (x2) for a replacement turbo.. not really a viable option in most consumer applications.