This does not work. Ctein has an excellent explanation of it in one of his books. I believe this is covered with print examples in "Post Exposure".
Basically, exposing a daylight negative film to tungsten light causes a bad mismatch in curves leading to bad results. Sorry. You need to use correction filtration to move between illuminants.
Another myth sad to say.
I agree (and this is why I loved shooting 320T so much, even having to push it), but it can be done on neg. film with acceptable results. Acceptable, not laboratory perfect. Often (for me) there is no other option. I would not bother filtering an 800 daylight film for tungsten light, as it would simply make it too slow.
"Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."
The Fujicolor amateur negative films from 100 to 1600 ASA (CN, CA, CH, CZ, and CU) are in general insensitive to the color shift by incandescent (tungsten) illumination. That may have been the reason why the 800 speed film has been so popular in photojournalism. Tungsten light is reproduced visually correct, and grain is similar to other brands' 200 ASA films.
Portra 800 gets a strong yellow to red color cast, similar to slide film.