Tuning your radiator cooling system

[pokismoki]

I know a few of you on here are old racers,  was wondering in your past experiences with race cars,  have you guys every pulled the thermostats out of the motor for full flow, and at then experimented with regulating the airflow thru the radiator instead?

 

if so what did you find out?

 

how much occlusion of the radiator is needed for decent warm up, cruising and high load [racing, towing] situations?  

 

what design did you go with to block the radiator? cardboard or fancy shutters?