75w90 works better with the cold feel of the box. Being a full synthetic PAO it is streaks ahead of a mineral 75w90 which would be fine in that application.
Ring Vertex themselves thats why they have technical people. Will save the secondhand information.
I'm not a vertex fan but as far as the oil spec goes its a PAO which is as good as it gets. Providing that is the oil they used and if it was I would doubt very much that it's an oil issue.
It has enough oil? What did they say?
Oh right yea. The people that make those claims on the internet havent had anything reasonable to compare it too. The real world difference is f all theyre both tiny and come on fast in transient conditions.
I'm guessing if they're V8 and equal length theyre twin scroll in which case they will take a lot of work to fit.
New turbo or exhaust housing
Up pipe bracket
Downpipe
Sump/windage tray/dipstick