Avions experimented with many engines, its favourite being the sleeve valve Knight engine, both 4 cylinder and 6, plus I understand a prototype V8. Later in some models the Graham 3.5 litre engine was used.
Another prototype around 1921 was a 7.2litre V12, also an inline twelve cylinder plus a prototype seven-cylinder radial. Now the radial would be interesting and I would like to know how it was fitted into a car as this would require some thoughtful engineering especially with the driveshaft.
This video shows 5 Avions at the Barrington Concurs, one is a 1933 model completely original and has never been restored.