I know a guy running a 443 cube FE with a 1/2 filled block on the street (100+ deg weather) with no problems. Note that some OEM blocks have shallow waterjackets. What makes this possible is the fact that the bulk of the heat is near the head where the combustion takes place. I've spoken with a couple of engine builders that 1/2 fill street motors. They both say that water temp will stay under control with a good cooling system but that
oil temperature may still rise. Both recommmend a good
oil cooler. You can't simply rely on
synthetic oil either since bearings will sweat the softer metal at high temperature.
You do need to have the waterjacket very clean when doing the fill and should fill the block before boring and honing. I'd have the main caps in place and torqued to spec.
This is an important matter for me too, since my 486 FE is half filled.
Dan Jones
Dan Jones