Thanks Basjoos, the added hole worked just fine today, and I left the closeable half shut all day. When I was under the car yesterday I noticed that my furnace grate still had all its louvers in place and angled to both edges. I think I was just adding to much resistance to get enough air through it. I cut off the fins and just kept the open and closing parts
Also I have an belly pan under the engine (some air can get out the back but not much) so the air is forced out into the back half of the wheel wells.
The first opening is 4x13" and the furnace grate is 3x13" the second hole I made is 4x 10.5". this gives me 42sq in always open (except in winter I plan on covering this hole) and another 40 or so that are operable. all in all its the same as I had before with my two grates in my lower grill.
I am planning on making a metal cover for the second hole and using that once the summer heat is gone say mid sept-may. this will give me control of airflow for most of the year and only when I need more then one open I will take off the cover.