Hey Dave, have had a project Corvair sitting here for a few years now and have been thinking of mid-mounted radiator - don't like the idea of cutting up the front end. Was thinking about your cooling issues.
Seems something is causing a higher pressure in the back of the radiator and stagnating the air - if it were reverting you'd still have airflow and some cooling. It would either be the cove panel acting like a scoop or the back cowl area adding pressure... or both, I remember reading someone had done some testing on that cowl many years ago but don't remember the results offhand, old brain.
I remember reading an article a few weeks ago, that of course I cant find now but it was talking about using the negative pressure from a venturi tunnel/rear diffuser to evacuate air from exhaust systems and cooling systems similar to the way a header pulls negative pressure in the exhaust collector.
It mentioned that using the rear most area of the diffuser lip as the most efficient place to exhaust air as it would disturb the airflow the least inside the tunnel.
The panel under the bumper in the back where the old heat flaps go could be removed and would be a good place to integrate a venturi tunnel.
https://www.google.com/search?hl=en&biw ... 4176324490
https://www.google.com/search?hl=en&biw ... 4176324490