Winter cover issues please help

Im trying to cover the grill on my Classic with Detroit 14l...other guys are doing it in the yard with cardboard and saving alot on fuel (gets cold and windy up here...these days -10 to -25 celcius). I tried doing it...covering different parts of the grill but my engine does not respond well at all. I get overboosting and serious power loss. So is there an exact dimension and position NOT to restrict airflow? Im not understanding this at all...

 

Ok i know im not cheap...but before even shelling out a C note for a winter front and risking it do the same thing why not ask about why im having this issue?? The first piece i tried i cut like the pete one with the triangle in the middle...same for the Freight. I got nasty power and overboost just the same. These other dudes run tiny grilled trucks probly not the same flow going on. I dont care what its made of as long as it works...i can always put the cardboard inside the hood anyway. Mechanical opinions plz. Thnx

 

Yeah its been done. The air to air is new. Withouth the anything over the grill it runs great...doesnt go over 40 lbs of boost and pulls good. Real bizarre

 

Air cleaners are outside. I run without but my engine runs way below temp...155 or so. Had the thermostats changed 4 days ago...helped a tad but still running cold...guage wise and i can tell by how much louder the engine runs. Well it seems like a mystery. Lets hope this brutal winter shuts off soon.