RILEY SPECS - V8as Old as the Industry, as modern as the Hour
It is entirely possible that the V8 experiment was the cause of Riley's demise. The 8/90 was an expensive failure, for no particular reason, and while the Autovia had outside backers, Riley took the brunt of it's losses. The engines were highly acclaimed at the time, but it was the wrong time.
The 8/90 was an 18hp engine (being two Riley 9's), and so under the normal Riley coding it should have been called an 18/8. However, for whatever reason Riley instead decided to use the nomenclature 8/90, reflecting the V8 engine with 90 degrees between cylinder banks. Doubtless the '90' sounds a lot bigger and better than a mere '18' would have done!
The Autovia engine was a 24hp unit (as it was two Riley 12's).