I am on the McLaren forums as well and have been following this one a bit. Quite impressive for a mostly stock car. Upgraded stock turbo internals, catless exhaust and tune only. The 3.8l was and still is a monster from all of their other models but this 4.0l is stepping it up.
There is another one from Excell motor sports. Ran 9.21 at 154mph with tune and exhaust only. They had the record for a couple days. Still do for stock turbo 720.